11th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions

The forward geometry of the LHCb detector provides unprecedented access to both the very high and very low regions of Bjorken $x$ inside the nucleon. With full particle ID and a fast DAQ, LHCb is able to fully reconstruct plentiful charged particles and ${\pi }^0$ mesons, as well as relatively rare probes such as $Z$ bosons and heavy quarks, providing a unique set of constraints on nucleon structure functions. This talk will discuss recent LHCb measurements sensitive to intrinsic charm within the proton, modification of parton distribution functions inside the nucleus, and show the impact of recent LHCb measurements that dramatically reduce nPDF uncertainties at low $x$.

In the early stages of heavy-ion collisions, at the highest energies, the system begins in a highly anisotropic state which is far from equilibrium. At later times, the dynamic evolution of the system is well described in the framework of relativistic hydrodynamics which requires local thermodynamic equilibrium. The KoMPoST framework has had some success in bridging the gap between these descriptions via a coarse-grained, non-equilibrium evolution of the system assuming a medium dominated completely by gluons. In this work, we present new results in this framework which include quark degrees of freedom in the response of the system to perturbations from the non-equilibrium background.

High energy nuclear collisions produce far-from-equilibrium matter with a high density of gluons at early times. We identify for the first time two local order parameters for condensation, which can occur as a consequence of the large density of gluons. We demonstrate that an initial over-occupation of gluons can lead to the formation of a macroscopic zero mode towards low momenta that scales proportionally with the volume of the system—this defines a gauge invariant condensate. The formation of a condensate at early times has intriguing implications for early time dynamics in heavy ion collisions.

Within a microscopic kinetic description based on the Boltzmann equation, we evaluate the importance of the pre-equilibrium stage in high-energy heavy-ion collisions for final state observables over a large range of viscosity and system size. We use our results to determine the range of applicability of an effective description in relativistic viscous hydrodynamics. We find that hydrodynamics provides a quantitatively accurate description of collective flow when the average inverse Reynolds number is sufficiently small and the early pre-equilibrium stage is properly accounted for. We discuss different possible treatments of the pre-equilibrium phase in kinetic theory, KoMPoST and hydrodynamics and assess their applicability.

Heavy quarks are produced in the early stage of heavy ion collisions due to their large mass, and experience the entire evolution of the QCD medium. The baryon-to-meson ratio, in particular, the ${\mathrm{\Lambda }}_c^{+}$/$D^0$ ratio, provides valuable information on charm hadronization mechanisms, testing the role of coalescence in the Quark-Gluon Plasma created in PbPb collisions. In $p$Pb collisions, heavy quarks are essential to study cold nuclear matter effects, which include the modification of nuclear parton distribution functions, energy loss in the nucleus, and other effects, providing a crucial baseline for interpreting PbPb measurements. In this talk, the first LHCb open charm measurement in PbPb collisions, the ${\mathrm{\Lambda }}_c^{+}$/$D^0$ ratio, will be presented. Moreover, this presentation will show precision measurements of open charm production from a rich set of charmed hadrons in $p$Pb collisions at 5.02 and 8.16 TeV, including the first measurement of ${\mathrm{\Xi }}_c^{+}$ baryons in heavy ion collisions. The nuclear modification factor $R_{p\mathrm{Pb}}$, forward-backward ratio $R_{\mathrm{FB}}$ and particle production ratios of charm baryons and mesons will be discussed and compared to models.

We consider the problem of including a finite number of scattering centers in dynamical energy loss and classical DGLV formalism. Previously, either one or an infinite number of scattering centers were considered in energy loss calculations, while attempts to relax such approximations were largely inconclusive or incomplete. In reality, however, the number of scattering centers is 4-5 at RHIC and the LHC, making the above approximations inadequate and this theoretical problem important for QGP tomography.

We derived explicit analytical expressions for dynamical energy loss and DGLV up to the 4th order in opacity, resulting in complex mathematical expressions that were, to our knowledge, obtained for the first time. These expressions were then implemented into an appropriately generalized DREENA framework to calculate the effects of higher orders in opacity on a wide range of high-pt light and heavy flavor predictions. Results of extensive numerical analysis, including their intuitive interpretations, will be presented.

A nonperturbative charm production contribution, known as intrinsic charm, has long been speculated. While it has yet to be satisfactorily proven, there have been recent tantalizing hints. Several experiments, either taking data or
planned, could proivde definitive evidence in the next few years. Experiments that have taken $J/\psi$ and $D$ meson data include SeaQuest at Fermilab and SMOG at LHCb, see Refs. [1,2] and references therein. Future experiments such as NA60+ are in an energy regime where the intrinsic charm quark signature could be large and unmistakeable, as discussed in recent work [3]. These predictions are discussed and compared to previous fixed-target data.

R. Vogt, Limits on Intrinsic Charm Production from the SeaQuest Experiment, Phys. Rev. C 103 (2021), 035204.

R. Vogt, Contribution from Intrinsic Charm Production to Fixed-Target Interactions at the LHC, to be submitted.

R. Vogt, Energy dependence of intrinsic charm production: Determining the best energy for observation, Phys. Rev. C 106 (2022) 025201.

This work was performed under the auspices of the U.S.\ DoE by LLNL under Contract DE-AC52-07NA27344 and supported by LDRD projects 21-LW-034 and 23-LW-036.

The Low's theorem is applied to the soft gluon emission from heavy quark scattering in quark-gluon plasma (QGP). The QGP is described by the DQPM (Dynamical QuasiParticle Model) which reproduces the EoS from lQCD at finite temperature and chemical potential. We show that if the emitted gluon is soft and of long wavelength, the scattering amplitude can be factorized into the scattering part and the emission part and the Slavnov-Taylor identities are satisfied in the leading order. Imposing a proper upper limit on the emitted gluon energy, we obtain the scattering cross sections of charm quark as well as the transport coefficients (momentum drag and diffusion) in the QGP with and without gluon emission.

The main goal of the ALICE experiment is to study the physics of strongly interacting matter, including the properties of the quark-gluon plasma (QGP). The increase of relative production of strange hadrons with respect to non-strange hadrons is historically considered as one of the signatures of QGP formation during the evolution of the system created in heavy-ion collisions. Recent measurements performed in high-multiplicity proton-proton (pp) and proton-lead (p-Pb) collisions have shown features that are reminiscent of those observed in lead-lead (Pb-Pb) collisions. The microscopic origin of this phenomenon is still not fully understood: is it related to soft particle production or to hard scattering events, such as jets? To separate strange hadrons produced in jets from those produced in soft processes, the angular correlation between high-$p_{\mathrm{T}}$ charged particles and strange hadrons has been exploited. The near-side jet yield and the out-of-jet yield of $K_S^0$, $\mathrm{\Xi }$, and $\varphi$ have been studied as a function of the multiplicity of charged particles produced in pp collisions at $\sqrt{s}$ = 13 TeV and p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV. New results suggest that out-of-jet processes are the dominant contribution to strange particle production. The results of these measurements are compared to expectations from state-of-the-art phenomenological models implemented in commonly used Monte Carlo event generators.

The ALICE experiment at the Large Hadron Collider (LHC) is designed to investigate the properties of the quark-gluon plasma created in high-energy heavy-ion collisions. During the successful data-taking campaigns of LHC Run 1 and Run 2 (2009 - 2018), it recorded data for a variety of collision systems and different center-of-mass energies. As particle production at the LHC is driven by a complex interplay of soft and hard QCD processes, finding a consistent model description for all collision systems is challenging. The study of charged-particle production as a function of multiplicity plays a key role in understanding the properties of the matter created in small (pp, p-Pb) and large (AA) collision systems. The precise tracking capabilities from low to high transverse momentum of the ALICE apparatus give the unique opportunity to measure the evolution of multiplicity-dependent spectral shapes across collision system sizes and energies.

In this contribution, a comprehensive overview of charged-particle production measurements in pp, p-Pb, and AA collisions up to high transverse momentum will be presented. It is obtained by means of a two-dimensional unfolding approach that allows for a detailed correction of detector resolution effects and yields the spectral properties in high-granular multiplicity intervals, maximizing the measurement precision. The results will then be tested against the main theoretical models implemented in commonly used Monte Carlo event generators.

Diffusion wake accompanying the jet-induced Mach-cone provides a unique probe of the properties of quark-gluon plasma in high-energy heavy-ion collisions. It can be characterized by a depletion of soft hadrons in the opposite direction of the propagating jet. We explore the 3D structure of the diffusion wake induced by γ triggered jets in Pb+Pb collisions at the LHC energy within the coupled linear Boltzmann transport and hydro model. We identify a valley structure caused by the diffusion wake on top of a ridge from the initial multiple parton interaction (MPI) in jet-hadron correlation as a function of rapidity and azimuthal angle. This leads to a double-peak structure in the rapidity distribution of soft hadrons in the opposite direction of the jets as an unambiguous signal of the diffusion wake. Using a two-Gaussian fit, we extract the diffusion wake and MPI contributions to the double peak. The diffusion wake valley is found to deepen with the jet energy loss as characterized by the γ-jet asymmetry. Its sensitivity to the equation of state and shear viscosity is also studied.

Measurements of two-particle correlations in $pp$ collisions show the presence of long-range correlations along $\mathrm{\Delta }\eta$ that are strikingly similar to those seen in heavy-ion collisions. The similarity between the $pp$ and heavy-ion measurements raises the possibility that a tiny droplet of the QGP is produced even in $pp$ collisions. However, models that attribute the correlation in $pp$ collisions to semi-hard processes, can qualitatively reproduce the measurements. Performing the $pp$ measurements while distinguishing between the particles from semi-hard processes, such as low-$p_{\mathrm{T}}$ jets, and the particles produced from soft interactions, can differentiate between these two origins of the $pp$ ridge. This talk presents measurements of two-particle correlations in $pp$ collisions at $\sqrt{s}=13$ TeV with two different particle-pair selections. In the first case, tracks associated with jets are excluded from the correlation analysis. This is shown to affect the magnitude of long-range correlations by only a few percent. New measurements of two-particle correlations, measured between tracks that are constituents of jets and tracks from the underlying event are also presented. These measurements can further elucidate the origin of the $pp$ ridge.

Jets are excellent probes for studying the deconfined matter formed in heavy ion collisions. Measurements of jet yield and substructure as a function of jet resolution parameter $R$ over a wide range in jet $p_{\mathrm{T}}$ probe the mechanisms underlying the interaction between jets and the QGP, notably the role of opening angle of the hardest jet shower components, and of the angular distribution of medium-induced radiation. In this talk, we will present two measurements of the nuclear modification factor $R_{AA}$ in central Pb-Pb collisions at $\sqrt{s}=5.02$ TeV with ALICE, addressing the influence of the large uncorrelated background with novel techniques in machine learning and mixed event subtraction. The mixed-event technique, newly introduced in ALICE, enables inclusive jet measurements at low $p_{\mathrm{T}}$ with minimal bias, in a previously unexplored energy regime at the LHC. In addition, the machine learning method enables the measurement of the $R$-dependence of jet suppression for $R=0.6$ down to 40 GeV/c. Finally, we introduce a new infrared and collinear safe measurement of the jet energy flow within jets reconstructed with different resolution parameters $R$. Investigating how the energy is distributed for the same jet with different $R$ allows energy loss to be explored on a jet-by-jet basis instead of between different populations of jets as in inclusive measurements. These results are compared to jet quenching models.

The $R$-dependence of jet observables provides a new tool in understanding the interplay between the jet energy-loss mechanism and medium response in heavy-ion collisions. We have coupled the Monte Carlo event generators JEWEL and PYTHIA, with initial conditions from the ${\mathrm{T}}_{\mathrm{R}}\mathrm{E}\mathrm{N}\mathrm{T}\mathrm{o}$ and the state-of-the-art (2+1)D v-USPhydro, for the simulation of jet quenching phenomena in a more realistic medium formed in lead-lead collisions at LHC energy scales.

In this work, we present one of the first studies of the jet nuclear modification $R_{AA}$ and anisotropic flow coefficients $v_{n=2,3}$ as a function of the jet cone radius $R$, in the context of anti-$k_T$ jets, in addition to jet shape observables. The calculations indicate the impacts of the hydrodynamic evolution and weakly-coupled medium response, given by recoils, on the distributions. Results are compared to experimental data in a wide range of jet $p_T$ and collision centrality, and displayed along with large jets ($R\ge 0.6$) predictions.

High-energy partons are well established to lose energy when traversing the hot and dense medium produced in heavy-ion collisions. This results in a modification to the transverse momentum distributions of jets, producing a phenomenon known as jet quenching. It has been previously established in Pb+Pb collisions at $\sqrt{s_{\text{NN}}}=2.76$~TeV that jet quenching leads to significant modifications to the transverse momentum balance of dijet pairs. More differential measurements are needed to better understand the observed phenomenon. In this talk, we report new, fully unfolded measurements of the dijet momentum balance in Pb+Pb and $pp$ collisions at $\sqrt{s_{\text{NN}}}=5.02$~TeV as well as in Xe+Xe collisions at $\sqrt{s_{\text{NN}}}=5.44$~TeV. These measurements expand upon previous publications, including the per-event yield of dijets as a function of the momentum balance, which provides insight into the nature of jet quenching. This talk will additionally present a new observable, the d??et pair nuclear modification factors projected along leading and subleading jet transverse momentum, which provides a precise quantification of asymmetric energy loss experienced by dijets.

Jet energy loss and transverse momentum broadening are twin consequences of a jet interacting with a hot and dense QCD matter in heavy-ion collisions. The underlying interaction can be represented by jet transport coefficient $\hat{q}$ distributed in the whole phase space of the bulk medium. The gradient of $\hat{q}$ perpendicular to the momentum direction of an energetic parton leads to an asymmetry of the transverse momentum distribution, which can be used for the initial jet production localization. We investigate such an asymmetry caused by the subleading jet by triggering the leading jet propagating in-plane in Pb+Pb 0-10% collisions at $\sqrt{s}=5.02$ TeV. Simulations are performed in the linear Boltzmann transport model with fluctuating event-by-event 3+1D viscous hydrodynamic backgrounds. We find that the initial jet production vertex can be localized by combining the dijet transverse imbalance $x_J=p_T^{\mathrm{subleading}}/p_T^{\mathrm{leading}}$ and subleading jet transverse gradient asymmetry for different leading jet $p_T$ regions. The correlation between both quantities is also investigated to illustrate the properties of $\hat{q}$.

Measurements of quarkonia production in peripheral and ultra-peripheral heavy-ion collisions are sensitive to photon-photon and photon-nucleus interactions, the partonic structure of nuclei, and to the mechanisms of vector-meson production. LHCb has studied production of the $J/\psi$ and $\psi (2S)$ charmonium states in peripheral and ultra-peripheral collisions using PbPb data at forward rapidity, obtaining the highest precision currently accessible. Here we will present these measurements, along with comparisons with the latest theoretical models and with results from other experiments. Future UPC measurements with the upgraded LHCb detector in Run 3 will also be discussed.

Minijets, created by perturbative hard QCD collisions at moderate energies, can represent a significant portion of the total multiplicity of a heavy-ion collision event. Since their transverse momenta are larger than the typical saturation scale describing the bulk of the equilibrating QGP, they do not in general hydrodynamize at the same pace than the bulk of the collision. In this work we make use of a new concurrent minijet+hydrodynamic framework in which the properties of the fluid QGP are modified due to the injection of energy and momentum from the minijets. In order to achieve a realistic description of charged particle multiplicity, the amount of entropy associated to the low-$x$ initial state needs to be reduced. Moreover, the fact that the injected momentum from the randomly oriented minijets is not correlated with the spatial gradients of the system reduces overall flow, and the value of the QGP transport coefficients needs to be reduced. They are, in effect, an important new source of fluctuations. We avow that their abundance makes it necessary to include their physics in holistic descriptions of heavy-ion collisions. We discuss the impact of the minijets on a number of observables, such as $p_T$ spectra and $p_T$-differential flow $v_n$ for a wide range of centrality classes.

Based on: Minijet quenching in a concurrent jet+hydro evolution and the nonequilibrium quark-gluon plasma, D. Pablos, M.Singh, C. Gale, S. Jeon. Phys.Rev.C 106 (2022) 3, 034901

In relativistic heavy ion collisions, the charged ions produce an intense flux of equivalent photons. Thus, photon-induced processes are the dominant interaction mechanism when the colliding nuclei have a transverse separation larger than the nuclear diameter. In these ultra-peripheral collisions (UPCs), the photon provides a clean, energetic probe of the partonic structure of the nucleus, analogous to deep inelastic scattering. This talk presents a measurement of jet production in UPCs performed with the ATLAS detector using high-statistics 2018 Pb+Pb data. Events are selected using requirements on jet production, rapidity gaps, and forward neutron emission to identify photo-nuclear hard-scattering processes. The precision of these measurements is augmented by studies of nuclear break-up effects, allowing for detailed comparisons with theoretical models in phase-space regions where significant nuclear PDF modifications are expected but not strongly constrained by existing data.

We construct an improved 3+1D version of the Trento initial state model, which includes rapidity-dependent fluctuations. The correlation between the fluctuations at different rapidities is controlled by a new parameter. We then use this improved model to study rapidity-dependent observables for ultracentral collisions. It it known that ultracentral flow at midrapidity is sensitive to fluctuations in the initial state, and it is likewise expected that rapidity-dependent flow will be sensitive to the correlation of these fluctuations between different rapidities in the initial state.

We study the impact of the Glasma fields, used to describe the very-early stage of heavy-ion collisions, on the transport of hard probes, namely heavy quarks and jets. We perform numerical simulations of the strong classical fields using techniques from real-time lattice gauge theory. The resulting fields are used as background for the classical transport of ensembles of particles, described by Wong's equations. We develop a numerical solver for the transport of the probes, based on colored particle-in-cell methods.

We focus on the dynamics of heavy quarks and jets in the classical colored fields. To quantify the effect of the Glasma, we extract momentum broadening of hard probes and evaluate the anisotropy transfer from the Glasma to the probes. We investigate other ways to measure the imprint of the Glasma, such as two-particle angular correlations of quark pairs or gauge invariant correlators of color Lorentz forces exerted on the probes.

A. Ipp, D. I. Muller, D. Schuh - Jet momentum broadening in the pre-equilibrium Glasma
P. Khowal, S. K. Das, L. Oliva, M. Ruggieri - Heavy quarks in the early stage of high energy nuclear collisions at RHIC and LHC
D. Avramescu, V. Băran, V. Greco, A. Ipp, D. I. Müller, M. Ruggieri - Simulating jets and heavy quarks in the early stages of heavy-ion collisions using the colored particle-in-cell method (in preparation)

Charmonia production in RHIC is one of the best probes of the QGP state of matter which is created in those collisions. However, the genuine origin of such charmonia is under debate: statistical hadronisation (SH) model considers them as formed at the freeze out while transport models contain 2 components : the primordial charmonia, produced early and subject to decay rate as well as the continuous regenerated component enabled once the local temperature falls below the dissociation temperature. While the SH and transport models can describe the present data, they suffer from some shortcomings.
In our new approach (arxiv 2206.01308), we take strong inspiration from the open quantum system method and propose a microscopic model based on the evaluation of a creation/destruction rate (following Remler's model) from the set of all c and cbar correlated trajectories generated by combining c and cbar scatterings with the QGP and c-cbar potential estimated from lQCD calculations. This allows to describe the continuous generation of charmonia over time while preserving essential features of the quantum transport.
Comparison with LHC data demonstrates that our model is able to reproduce the global trends. In a 2nd version of our model to be presented at HP, we implement our approach in the newly relased EPOS4 and study in particular the role of c-cbar corrrelations in the initial stage as well as the contribution of the excited states, missing in the 1rst version of our model.

Quarkonia are excellent probes of deconfinement in heavy-ion collisions. For J/$\psi$, a bound state of $c\overline{c}$ quarks, its production yield is sensitive to color screening and dissociation in the medium. However, at LHC energies, the charmonium regeneration is expected to be significantly larger than at RHIC and SPS energies, since the density of uncorrelated charm-anticharm ($c\overline{c}$) pairs in the medium is larger. On the other hand, the determination of the non-prompt component of the J/$\psi$ production, originating from b-hadron decays, allows one to access the interaction of b-quarks with the QGP. It enables as well for prompt J/$\psi$ measurements a direct comparison with prompt charmonium models.

In this talk, new published inclusive J/$\psi$ yield and nuclear modification factor results at midrapidity and forward rapidity, will be shown in Pb–Pb collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}$ = 5.02 TeV. The J/$\psi$-to-D${}^0$ meson ratio, obtained in central and semicentral collisions, will also be discussed. The preliminary measurements of prompt and non-prompt J/$\psi$ yields and nuclear modification factors, performed at midrapidity in Pb–Pb collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}$ = 5.02 TeV, will be presented. The determination of the non-prompt J/$\psi$ fraction extends down to very low $p_{\mathrm{T}}$ with a significantly improved precision compared to previous publications. Results will be compared with available calculations.

The second-order Fourier coefficients ($v_2$) of $\mathrm{{\rm Y}}$(1S) and J/$\psi$ mesons in high-multiplicity pPb collisions is studied using data collected by the CMS experiment at a nucleon-nucleon center-of-mass energy 8.16 TeV. The dimuons used to reconstruct the heavy quarkonium states are correlated with charged hadrons using long-range two-particle correlation techniques. The measurement of the $\mathrm{{\rm Y}}$(1S) $v_2$ is reported for the first time in small collision systems. The results are discussed in the context of collectivity and modification of heavy quark dynamics.

The second- and third-order Fourier coefficients of charmonium states are measured in PbPb collisions with CMS. With this new analysis, extending to a higher $p_{\mathrm{T}}$ region, we investigate further the high-$p_{\mathrm{T}}$ J/$\psi$ $v_2$ in heavy ion collisions. The nonprompt J/$\psi$ $v_2$ probes the different behavior of charm and bottom quarks induced by interactions with the QGP medium. The $v_3$ flow coefficient values, for the separated prompt and nonprompt J/$\psi$ as well as the prompt $\psi$(2S), are reported for the first time.

Suppression of open heavy flavors and quarkonia in heavy-ion collisions is among the most informative probes of the quark-gluon plasma. Interpreting the full wealth of data obtained from the collision events requires a precise understanding of the evolution of heavy quarks and quarkonia as they propagate through the nearly thermal and strongly coupled plasma. Only in the past few years, systematic theoretical studies of quarkonium time evolution in the QGP have been carried out in the regime where the temperature of the QGP is much smaller than the inverse of quarkonium size.

Such calculations require the evaluation of a gauge-invariant correlator of chromoelectric fields dressed with Wilson lines, which is similar to, but different from, the correlation used to define the well-known [1] heavy quark diffusion coefficient. The origin of this difference has been explained in [2-4]. In this talk, we will show a calculation of the analogous correlator in strongly coupled $\mathcal{N}=4$ SYM using the AdS/CFT correspondence at a finite temperature [5]. While it resembles the open heavy quark case, it has some crucial differences that highlight the relevance of quantum color correlations. We will also discuss the results for the quarkonium transport coefficients obtained from this correlator, thereby establishing the first analytic results at strong coupling in this context.

[1] Phys. Rev. D 74 (2006) 085012; [2] JHEP 01 (2022) 137; [3] arXiv:2205.04477; [4-5] in preparation

Jet-medium interactions receive large non-perturbative contributions from classical gluons, i.e. infrared gluons with high occupation numbers. These contributions affect transverse jet momentum broadening and medium-induced radiation. Both depend significantly on the in-medium dispersion of hard partons, encoded in their so-called asymptotic mass.
In this talk, I shall show how the analytical properties of thermal amplitudes allow for a non-perturbative determination of the IR classical contribution through lattice determinations in the dimensionally-reduced Effective Theory of hot QCD, EQCD. I will show how these existing lattice determinations need to be complemented by perturbative two-loop matching calculations in EQCD and QCD, so that the unphysical (classical) UV behaviour of EQCD is replaced by its proper quantum QCD counterpart. I will show how lattice and perturbative EQCD are in excellent agreement in the UV and I will discuss the numerical effect of the two-loop quantum QCD contribution, with an outlook on the effect on medium-induced radiation rates.
The talk is based on G.D. Moore, N. Schlusser 2009.06614, J. Ghiglieri, G.D. Moore, P. Schicho, N. Schlusser 2112.01407, J. Ghiglieri, P. Schicho, N. Schlusser, E. Weitz, in preparation

Jets produced from hard scatterings of partons early in heavy-ion collisions traverse through the quark-gluon plasma (QGP) medium and get modified relative to vacuum ($p$+$p$ collision) baseline. These modifications can change the distributions of jet shape observables, which are related to jet fragmentation and its internal structure, and calculated based on the intra-jet angular energy distribution. LHC results showed medium-induced modifications to differential jet shape ($\rho (r)$, radial distribution of constituents relative to the jet axis) distributions and a prevalence of quark-like fragmentation from Girth (jet angularity), $p_T^D$ (jet momentum dispersion) and LeSub (splitting between leading and subleading jet constituents) measurements. At RHIC, we are able to study lower energy jets, complementary to those measured at the LHC. Hence measurements of jet shapes at RHIC can help constrain models at different energy scales. In this talk, we present measurements of the fully corrected $\rho (r)$ in $p$+$p$ and Au+Au collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}=200$ GeV collected by the STAR experiment. We also show fully corrected resutls for Girth, $p_T^D$ and LeSub in $p$+$p$ collisions. Exploratory studies of these observables in Au+Au collisions will also be discussed.

We will discuss the use of recoil-free jet observables to systematically benchmark jet modification studies with precision and sensitivity, starting from the hardest components of jets. Here we focus on the recoil-free jet axis in defining di-jet and photon-jet angular decorrelation. This observable is not affected by the huge underlying event background and can be calculated and measured precisely. Also, since the recoil-free axis follow the dominant energy flow within jet, it is sensitive to any partonic energy loss mechanism which can deflect the axis direction. We will present Monte Carlos studies based on simulations with different jet quenching models. Future measurements of this observable will allow us to test the onset of jet quenching in the whole jet evolution history. This paves a path towards precision heavy ion jet modification studies using recoil-free observables.

The transverse momentum broadening coefficient serves as a key ingredient in characterising the quenching of a jet as it propagates through the QGP. While it has recently been understood to receive quantum, radiative corrections featuring potentially large logarithmic enhancements at relative order $g^2$ [1, 2], it is still not clear how these corrections compare quantitatively with their classical counterparts, i.e, those coming from the exchange of thermal gluons with large occupation number, present at relative order $g$ and higher [3–5].

During the talk, I plan to first motivate the need for a more careful calculation of the aforementioned logarithmic corrections in the case of a weakly coupled QGP. I will then sketch how the argument of the leading logarithm is altered with respect to earlier calculations and furthermore, how the phase space giving rise to these logarithmic corrections is smoothly connected to that from which the classical corrections emerge. Finally, I will conclude by discussing how these findings, detailed in our own work [6] are relevant with respect to the overall goal of determining which class of corrections are quantitatively more important.

[1] T. Liou, A. Mueller and B. Wu 1304.7677
[2] J.P. Blaizot, F. Dominguez, E. Iancu and Y. Mehtar-Tani 1311.5823
[3] S. Caron-Huot 0811.1603
[4] M. Panero, K. Rummukainen and A. Sch ̈afer 1307.5850
[5] G.D. Moore and N. Schlusser 1911.13127
[6] J. Ghiglieri and E. Weitz 2207.08842

The measurement of jets recoiling from a trigger hadron provides unique probes of medium-induced modification of jet production. Jet deflection via multiple soft scatterings with the medium constituents or single-hard Molière scatterings off quasi-particles in the medium are expected to modify the azimuthal correlation between the trigger hadron and recoiling jet. The $R$-dependence of recoil jet yield also probes jet energy loss and intra-jet broadening. In this talk we present measurements of the semi-inclusive distribution of charged-particle jets recoiling from a trigger hadron in pp and Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV. We employ precise, data-driven subtraction of the large uncorrelated background contaminating the measurement in Pb-Pb collisions, enabling the exploration of medium-induced modification of jet production and acoplanarity over a wide phase space, including the low jet $p_{\mathrm{T}}$ region for large jet resolution parameter $R$. Hadron-jet acoplanarity in pp collisions will be also presented, which provides a sensitive test of pQCD calculations, as well as a crucial data reference for in-medium jet deflection studies in Pb-Pb collisions. We observe that the jet yield at low $p_{\mathrm{T}}$ and at large azimuthal angle between the trigger hadron and jet is significantly enhanced in Pb-Pb collisions with respect to pp collisions. Comparison to theoretical calculations incorporating jet quenching will also be discussed.

Following the formalism developed in our preceding works [1], a non-perturbative light-front Hamiltonian approach, we investigated the momentum broadening of a quark jet inside a SU(3) colored medium. We performed the numerical simulation of the real-time jet evolution in the Fock space of |q> + |qg>, at an extensive range of $p^{+}$, and various medium densities. With the obtained light-front wavefunctions of the quark jet, we extracted the jet's observables, including its transverse momentum distribution, the quenching parameter, and the gluon emission rate. We analyzed the interplay between the medium-induced gluon emission and the momentum broadening. This work provides an enhanced understanding of jet quenching from non-perturbative perspectives.

[1] M. Li, T. Lappi, and X. Zhao, ``Scattering and gluon emission in a color field: A light-front Hamiltonian approach'', Phys. Rev. D 104 (2021) no.5, 056014; arXiv:2107.02225 [hep-ph].

Jet substructure observables provide unique probes of the properties of the quark-gluon plasma (QGP). In this talk, we report new measurements of groomed jet substructure in central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. We present the first application of Dynamical Grooming in heavy-ion collisions to search for excess $k_{\mathrm{T},\mathrm{g}}$ emissions as a signature of point-like scattering, which is sensitive to large-angle scattering of jets off of quasi-particles in the QGP. These results are reported for the first time in central Pb-Pb collisions and over a larger jet $p_{\mathrm{T}}$ range than reported previously. Additionally, we present measurements employing both the Soft Drop and Dynamical Grooming algorithms, comparing results in central Pb-Pb, semicentral Pb-Pb, and pp collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. Results with grooming methods and parameters will also be compared. The techniques developed for this measurement are more broadly applicable to jet substructure, which we will explore further in this talk. Comparisons to model calculations will also be discussed.

In a series of recent publications [1,2,3], we have proposed a factorized approach, based on perturbative QCD, for the evolution of a jet in a dense quark-gluon plasma, together with its implementation as a Monte-Carlo parton shower and successful applications to the phenomenology of jet quenching.
In the original formulation of the parton shower, the collisions between the jet constituents and those of the plasma have been treated in the multiple soft scattering approximation, thus neglecting important effects from single hard scattering. In this new work [4], we extend our Monte Carlo by including the effects of single scattering both on the transverse momentum broadening and on the spectrum for medium-induced radiation. To that aim, the medium-induced cascade is simulated in full 3+1 dimensions and collisions are generated dynamically. This allows us to complete the BDMPS-Z sector of the spectrum for medium-induced radiation with the GLV (Gyulassy-Levai-Vitev) tail at high energies and the Bethe-Heitler spectrum at low energies.
Finally, we discuss the impact of single hard scattering on jet substructure observables like the $k_{t,g}$-distribution after Soft Drop, as measured by the ALICE Collaboration.

Refs:
[1] Caucal, Iancu, Mueller, Soyez, PRL 120 (23), 232001
[2] Caucal, Iancu, Soyez, JHEP 2019 (10), 1-55
[3] Caucal, Iancu, Soyez, JHEP 2021 (4), 1-38
[4] Caucal, Iancu, Soyez, in preparation.

Measuring the jet substructure in heavy-ion collisions provides exciting new opportunities to study detailed aspects of the dynamics of jet quenching in the hot and dense QCD medium created in these collisions. In this talk, we present new ATLAS measurements of jet substructure performed using various jet (de)clustering and grooming techniques. Measurements of inclusive jet suppression ($R_{AA}$) in heavy-ion collisions are presented as a function of the jet substructure using both small-radius ($R=0.4$) and large-radius ($R=1.0$) jets in Pb+Pb and $pp$ collisions at $\sqrt{s_{NN}}=5.02$ TeV. The jet substructure is characterized using the Soft-Drop grooming procedure in order to identify subjets corresponding to the hardest parton splitting in the jet. The measurements are performed using different jet constituents such as charged tracks, smaller $R$ calorimeter jets, and novel objects reconstructed using tracker and calorimeter information. The dynamics of jet quenching is measured and presented as a function of the transverse momentum scale ($\sqrt{d_{12}}$) and the angle of the hardest splitting in the jet. These new measurements test the sensitivity of jet suppression in the QCD medium to its substructure and the emergence of a critical angle for the onset of color decoherence.

In recent years, there has been an effort towards establishing a more complete picture for jet substructure in the presence of the quark gluon plasma. Such a program requires not only a more detailed description of medium induced effects, but also the design of novel substructure observables. Very recently, it has been noticed that energy-energy correlators (EECs) might provide one type of such observables. Although the full extent of their sensitivity to the medium has not been completely explored, they are capable to resolve the transverse structure of the jet. In particular, they are sensitive to the critical angle separating coherent and decoherent jet evolution in the medium. In this talk, we show for the first time the effects of medium induced radiative energy loss in EECs at leading order in the number of vacuum-like emissions. The calculation takes into account all order soft gluon emissions, in the large $N_c$ limit and neglecting subdominant interfering contributions. Similar to other jet quenching observables, energy loss leads to an overall suppression of the EECs. More importantly, this is accentuated in the decoherent regime and results in an important competing effect when trying to extract the critical angle. We further comment on how the current calculation can be extended beyond leading order accuracy, important to compute more complex observables.

Hadronic collisions produce prompt photons that are characterized by a large transverse momentum and absence of event activity in their vicinity. Photons are a robust probe of cold nuclear matter effects in small and large collision systems because they do not interact strongly and are thus insensitive to medium-induced final-state effects. Prompt photon production is dominated by the Compton process ($g\text{q}\to \text{q}\gamma$), making it sensitive to the gluon parton distribution function (PDF), and provides a test of high momentum pQCD calculations. Recent experimental results indicate the need for corrections beyond NLO to describe their production accurately. This talk presents the measurement of isolated prompt photon production in pp and p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=8$ TeV, measured by ALICE. The isolation method is applied to suppresses the background photons produced in the fragmentation process and electromagnetic decays. The production cross sections in both systems will be presented and compared with NLO calculations using recent (n)PDFs and fragmentation functions. In addition, the nuclear modification factor $R_{\mathrm{p}\mathrm{A}}$ is measured, quantifying possible modifications of the parton distributions inside the nucleus. This is the first time the isolated prompt photon $R_{\mathrm{p}\mathrm{A}}$ has been measured for low transverse momenta of $p_{\mathrm{T}}<20$ GeV/$c$ - a regime in which a sizeable suppression is predicted by theoretical calculations.

Relativistic heavy-ion beams at the LHC are accompanied by a large flux of equivalent photons, leading to multiple photon-induced processes. This talk presents a series of measurements of dilepton production from photon fusion performed by the ATLAS Collaboration, which provide strong constraints on the nuclear photon flux, its dependence on the impact parameter and photon energy, and can also probe physics beyond the standard model (BSM) using tau leptons. Recent measurements of exclusive dielectron production in ultra-peripheral collisions (UPC) are presented. Comparisons of the measured cross-sections to QED predictions from the Starlight and SuperChic models are also presented. Furthermore, measurements of muon pairs produced via two-photon scattering processes in hadronic (i.e. Non-UPC) Pb+Pb collisions are discussed. These non-UPC measurements provide a novel test of strong-field QED and may be a potentially sensitive electromagnetic probe of the quark-gluon plasma. These measurements include the dependence of the cross-section and angular correlation on the mean-$p_{\mathrm{T}}$ of the dimuon pair, the rapidity separation between the muons, and the pair angle relative to the second-order event-plane, all measured differentially as a function of the Pb+Pb collision centrality. The presented results are compared with recent theory calculations. Tau-pair production measurements can constrain the tau lepton's anomalous magnetic dipole moment (g-2), and a recent ATLAS measurement using muonic decays of tau leptons in association with electrons and tracks provides one of the most stringent limits available to date.

An important sign of the creation of the Quark-Gluon Plasma in heavy-ion collisions is the observation of jet energy-loss. Energetic, high transverse momentum ($p_T$) partons produced at the moment of initial hard scattering are influenced by the evolution history of the medium and lose energy via interactions. In this work we compare two models of low virtuality radiative energy loss: MARTINI [1] and CUJET [2] using the JETSCAPE framework. We integrate CUJET into the JETSCAPE workflow and perform full jet simulations using DGLV [3-5] radiative rates, for the first time. We consider strongly interacting probes (charged hadrons, jets, jet shape and jet fragmentation function) as well as electromagnetic probes; photons from jet-medium interactions have a similar structure to the gluon radiation channel but experience no final state interactions [6]. We present the first realistic calculation of jet-medium photons from CUJET and compare it to jet-medium photons from MARTINI. We find that these photons contribute significantly in the phenomenologically interesting intermediate $p_T$ domain ($4$-$12$ GeV).
[1] B. Schenke et al., Phys.Rev.C 80 (2009) 054913
[2] J. Xu et al., JHEP 08 (2014) 063
[3] M. Gyulassy et al., Nucl.Phys.B 571 (2000) 197-233
[4] M. Gyulassy et al., Nucl.Phys.B 594 (2001) 371-419
[5] M. Djordjevic et al., Nucl.Phys.A 733 (2004) 265-298
[6] C. Gale et al., Phys.Rev.C 105 (2022) 1, 014909

Electromagnetic probes such as photons and dielectrons are a unique tool to study the space-time evolution of the hot and dense matter created in ultrarelativistic heavy-ion collisions. At low dielectron invariant mass ($m_{\mathrm{e}\mathrm{e}}$), thermal radiation from the hot hadronic phase contributes to the dielectron spectrum via decays of $\rho$ mesons, whose spectral function is sensitive to chiral-symmetry restoration. At larger $m_{\mathrm{e}\mathrm{e}}$, thermal radiation from the quark–gluon plasma carries information about the early temperature of the medium. At LHC energies, it is nevertheless dominated by a large background from correlated heavy-flavour hadron decays affected by energy loss and flow in the medium. Complementary to the real photon measurements, dielectron data also allow the extraction of the real direct photon fraction, including thermal photons at low pair transverse momentum $p_{\mathrm{T},\mathrm{e}\mathrm{e}}$. In pp collisions, such measurement serves as a fundamental test of perturbative QCD calculations, and as a baseline for the studies in heavy-ion collisions. This talk will present the latest ALICE results on dielectron studies in Pb-Pb, and in minimum-bias and high-multiplicity pp collisions, at $\sqrt{s_{\mathrm{N}\mathrm{N}}}$ = 5.02 TeV and 13 TeV, respectively. The measurements are compared to simulations and expectations from theory.
Finally, the status of the Run 3 analysis will be reported.

We present a consistent photon production calculation from hadronic cross sections, including bremsstrahlung and 2-to-2 reactions, matching the usually employed thermal rates [1,2]. Using the hadronic transport approach SMASH as the afterburner for the hadronic stage at RHIC and LHC energies, we find a significant increase in the calculated momentum anisotropies of these photons due to microscopic non-equilibrium dynamics. This enhancement is found in comparison to standard calculations, which rely on the folding of equilibrium rates to a hydrodynamical evolution. Once combined with photons produced above the particlization temperature in the hydrodynamical evolution, the differences between the two approaches are modest regarding $p_{\perp }$-differential spectra, but are clearly noticeable at low for the elliptic flow: non-equilibrium dynamics enhance the photon $v_2$ below $p_{\perp }\approx 1.5$ GeV.

References
[1] A. Schäfer, O. G-M., J-F. Paquet, H. Elfner, and C. Gale. Phys.Rev.C 105 (2022) 4, 044910, arXiv: 2111.13603

[2] A. Schäfer, J. M. Torres-Rincon, J. Rothermel, N. Ehlert, C. Gale and H. Elfner. Phys.Rev.D 99 (2019) 11, 114021. arXiv: 2111.13603

Photon-induced reactions in ultra-peripheral collisions (UPCs) of heavy nuclei at the LHC have been studied using the ALICE detector for several years. The ALICE detector can measure the photoproduction cross section for vector mesons at various rapidities, centre-of-mass energies and collision systems. Beyond the recent ALICE studies of the rapidity and momentum transfer dependence of coherent $\mathrm{J}/\psi$ photoproduction, new results on incoherent $\mathrm{J}/\psi$ photoproduction will be discussed. These results complement coherent $\mathrm{J}/\psi$ measurements and provide additional sensitivity to probing nuclear gluon effects including the presence of subnucleon gluon fluctuations. Additionally, new measurements of the coherent and incoherent $\mathrm{J}/\psi$ polarization will be shown. These new results serve for testing the s-channel helicity conservation hypothesis.

The intriguing phenomena emerging in the high-density QCD matter are being widely studied in the heavy ion program at the LHC and will be understood more deeply during the high luminosity LHC (HL-LHC) era. The CMS experiment is under the Phase II upgrade towards the HL-LHC era. A new timing detector is proposed with timing resolution for minimum ionization particles (MIP) to be 30ps. The MIP timing detector (MTD) will provide the particle identification (PID) ability with a large acceptance covering up to $\eta <3$ through time-of-flight (TOF). Combining MTD with the other new sub-detectors, a tracker with acceptance $\eta <4$, high granularity calorimeters with acceptance covering $\eta <5$, will enable the deep studies of high-density QCD matters in ultra-relativistic heavy ion collisions. In this presentation, the performances of a broad range of measurements in heavy ion programs will be discussed using TOF-PID. These include the (3+1)D evolution of heavy flavor quarks, QGP medium response to high-$p_{\mathrm{T}}$ parton energy loss at wide jet cone angles, collectivity in small systems, fluctuations and transport of initially conserved charges, and light nuclei physics.

ALICE 3 is proposed as the next-generation experiment to address unresolved questions about the quark-gluon plasma by precise measurements of heavy-flavour probes as well as electromagnetic radiation in heavy-ion collisions in LHC Runs 5 and 6. In order to achieve the best possible pointing resolution a concept for the installation of a high-resolution vertex tracker in the beam pipe is being developed. It is surrounded by a tracker based on monolithic active CMOS pixel sensors covering roughly 8 units of pseudorapidity. To achieve the required particle identification performance, a combination of a time-of-flight system and a Ring-Imaging Cherenkov detector is foreseen. Further detectors, such as an electromagnetic calorimeter, a muon identifier, and a dedicated forward detector for ultra-soft photons, are being studied. In this presentation, we will explain the detector concept and its physics reach as well as discuss the R&D challenges.

In Spring 2023, the sPHENIX detector at BNL’s Relativistic Heavy Ion Collider (RHIC) will begin measuring a suite of unique heavy flavor and quarkonia observables with unprecedented statistics and kinematic reach at the RHIC energies using combined EM and hadronic calorimeters and high precision tracking. A MAPS-based vertex detector upgrade to sPHENIX, the MVTX, will provide a precise determination of the impact parameter of tracks relative to the primary vertex in high multiplicity heavy-ion collisions and polarized proton-proton/proton-nuclei collisions. It will enable precision measurements of open heavy-flavor observables, covering an unexplored kinematic region at RHIC. The physics program, its potential impact, and the recent detector development will be discussed in this talk.

The high-intensity beams provided by the CERN SPS in a wide energy interval offer a unique opportunity to investigate the region of the QCD phase diagram at high baryochemical potential. The NA60+ experiment, proposed for taking data with heavy-ion collisions at the SPS in the next years, has a strong potential for investigating the QCD phase diagram via measurements of rare probes in a beam-energy scan of Pb-Pb and p-A collisions in the interval √s${}_{NN}$ = 6-17 GeV.
In this talk the physics program of the NA60+ on thermal dimuons will be described.
At beam energies below top SPS energy, the baryon density becomes maximal and its effect on $\rho$ meson broadening can be measured by NA60+ with utmost precision.
NA60+ will have sensitivity to the $\rho -a_1$ chiral mixing mechanism, which provides access also to the properties of the $a_1$ by exploring the thermal dimuon mass spectrum in the range 1 < M < 1.4 GeV.
For dimuon masses above 1.5 GeV, the temperature of the emitting source can be directly extracted by a fit of the mass spectrum. The experimental program of NA60+ plans to determine for the first time a caloric curve by measuring the temperature vs beam energy, with particular focus on √s${}_{NN}$ < 10 GeV, which is believed to be essential to map out the phase transition regime at high ${\mu }_B$.
Finally, the competitiveness and complementarity of NA60+ in the landscape of the experiments foreseen at other facilities in the next decade will be discussed.

The addition of a Forward Calorimeter (FoCal) to the ALICE experiment is proposed for LHC Run 4 to provide unique constraints on the low-x gluon structure of protons and nuclei via forward measurements of direct photons. A new high-resolution electromagnetic Si-W calorimeter using both Si-pad and Si-pixel layers is being developed to discriminate single photons from pairs of photons originating from ${\pi }^0$ decays. A conventional sampling hadron calorimeter is foreseen for jet measurements and the isolation of direct photons. In this presentation, we will report on results from recent test beam campaigns at CERN with Si-pad and pixel modules, a first prototype for the hadronic calorimeter, as well as the physics prospects.

After the successful installation and first operation of the upgraded Inner Tracking System (ITS2), which consists of about 10 m${}^2$ of monolithic silicon pixel sensors, ALICE is pioneering the usage of bent, wafer-scale pixel sensors for the ITS3 for Run 4. Sensors larger than typical reticle sizes can be produced using the technique of stitching. At thicknesses of about 30 µm, the silicon is flexible enough to be bent to radii of the order of 1 cm. By cooling such sensors with a forced air flow, it becomes possible to construct a detector with minimal material. The reduction of the material budget and the improved pointing resolution will allow new measurements, in particular of heavy-flavour decays and electromagnetic probes. In this presentation, we will report on the sensor developments, the performance of bent sensors in test beams, and the mechanical studies on truly cylindrical layers.

Measurements of bottomonium states in heavy-ion collisions provide a powerful tool to study both initial-state effects on heavy-quark production and final-state interactions between heavy quarks and the quark-gluon plasma (QGP). The ATLAS experiment at LHC has measured the production of bottomonium states $\mathrm{{\rm Y}}$(1S), $\mathrm{{\rm Y}}$(2S), and $\mathrm{{\rm Y}}$(3S), in Pb+Pb and $pp$ collisions at a center-of-mass energy per nucleon pair of 5.02 TeV. The data correspond to integrated luminosities of 1.38 nb${}^{-1}$ of Pb+Pb data collected in 2018, 0.44 nb${}^{-1}$ of Pb+Pb data collected in 2015, and 0.26 fb${}^{-1}$ of pp data collected in 2017. The final ATLAS result on the production of three bottomonium states will be reported. The measurement in Pb+Pb collisions is compared to that in $pp$ collisions to extract the nuclear modification factor, $R_{\mathrm{AA}}$, as a function of event centrality, $p_{\mathrm{T}}$ and rapidity, and compared to several theoretical models. We will also present a new measurement studying the relationship between the production of hard and soft particles through the correlation of Upsilon meson states with the inclusive-charged particle yields. The analysis is performed using the full-luminosity ATLAS Run-2 13 TeV $pp$ data. A description of the technical challenges associated with a heavy-ion style analysis in high-pileup $pp$ data will be shown, as well as the results and their physics implications.

We present the first study of coherent exclusive quarkonium (J/psi, Upsilon) photoproduction in ultraperipheral nucleus-nucleus collisions (UPCs) at the LHC in the framework of collinear factorization and next-to-leading order (NLO) perturbative QCD. We make predictions for the J/psi and Upsilon rapidity distributions for the cases of lead (Pb) and oxygen (O) beams and quantify their dependence on the choice of the hard scale, nuclear PDFs and their uncertainties, and models for nuclear generalized parton distribution functions (GPDs). We demonstrate that our approach provides a simultaneously good description of all available Run 1 and Run 2 LHC data on J/psi photoproduction in Pb-Pb UPCs and makes definite predictions for photoproduction of heavy quarkonia in heavy-ion UPCs at the LHC.

We extend a previously constructed T-matrix approach for heavy quarks in the quark-gluon plasma (QGP) to include inverse-mass (1/M) corrections, i.e. the spin-orbit, spin-spin and tensor forces, between partons. Based on the vacuum Cornell potential as the interaction kernel for the T-matrix equation, we first confirm that the experimental charmonium and bottomonium spectroscopy in vacuum are much improved by employing a confining potential that is a mixture of vector and scalar interactions, rather than a purely scalar one. We then apply the refined potential to calculate the in-medium single-parton spectral functions at finite temperature self-consistently and constrained by various thermal lattice-QCD data. Finally, we study the consequences for the in-medium charm-quark transport coefficients at different temperatures. It turns out that the mixing effect for confining potential significantly enhances the friction coefficient, A(p), for charm quarks in the QGP over previous calculations with a purely scalar potential. Our results may have significant implications for the microscopic description of heavy-flavor transport in heavy-ion collisions at RHIC and the LHC.

The LHCb spectrometer has the unique capability to function as a fixed-target experiment by injecting gas into the LHC beampipe while proton or ion beams are circulating. The resulting beam+gas collisions cover an unexplored energy range that is above previous fixed-target experiments, but below the top RHIC energy for AA collisions. Here we present new results on open charm, $J/\psi$, and $\psi (2S)$ production from pNe and PbNe fixed-target collisions at LHCb. Comparisons with various theoretical models of particle production and transport through the nucleus will be discussed.

Heavy quarks (i.e. charm and beauty) are powerful tools to characterize the quark-gluon plasma (QGP) produced in heavy-ion collisions. Although they are initially produced out of kinetic equilibrium via hard partonic scattering processes, recent measurements of anisotropic flow of charmed hadrons [1] pose the question regarding the possible thermalization of heavy quarks in the medium. Our recent work [2] provides new insights on the level of thermalization of charm and bottom quarks in the QGP. In particular, exploiting a mapping between transport theory and fluid-dynamics, we will show how a fluid-dynamic description of the dynamics of charm quarks in the QCD plasma is feasible.
We will show results for spectra and flow coefficients of charmed hadrons obtained with a fluid-dynamic code (FluiduM [3]) coupled with the conservation of a heavy-quark - antiquark current in the QGP. We compare our calculations with the most recent experimental data in order to provide further constraints on the transport coefficients of the QGP [4].
This work is funded via the DFG ISOQUANT Collaborative Research Center (SFB 1225).
[1] PLB 813 (2021) 136054
[2] Phys.Rev.D 106 3, 034021 (2022)
[3] Phys. Rev. C 100, 014905 (2019)
[4] Capellino, Beraudo, Dubla, Floerchinger, Grossi, Kirchner, Masciocchi, Selyuzhenkov; in preparation

Bottomonia, the heaviest known mesons, represent major probes of strongly interacting matter properties. In the context of nuclear collisions, the binding energies separating the $\mathrm{{\rm Y}}$(nS) states (n=1, 2, or 3) offer an experimental handle to characterize the medium formed. In this talk, we study the modification of the production of the three $\mathrm{{\rm Y}}$ mesons in both pPb and PbPb collisions with the latest measurements carried out with the CMS detector. The results are compared with model calculations in order to interpret the data.

The leading jet transport coefficients $\hat{q}$ or ${\hat{e}}_2$ encode transverse or longitudinal momentum broadening of a hard parton traversing a hot medium. Computing their normalization and temperature dependence from first principles is key to appreciating the observed suppression of high-transverse momentum probes at RHIC or LHC collision energies. We present a first continuum extrapolated result of $\hat{q}$ computed on pure SU(3) lattices with non-trivial temperature dependence different from the weak-coupling expectation.

We discuss the formalism published in Refs [1,2] and its challenges and status in view of obtaining ${\hat{e}}_2$ or of unquenching the calculation. We consider a hard quark subject to a single scattering on the plasma. The transport coefficients are factorized in terms of matrix elements given as integrals of non-local gauge-covariant gluon field-strength field-strength correlators. After the analytic continuation to the deep-Euclidean region, the hard scale permits to recast these as a series of local, gauge-invariant operators. The renormalized leading twist term in this expansion is closely related to static quantities, and is computed on pure SU(3) lattices ($n_{\tau }$=4, 6, 8 and 10) for a range of temperatures, ranging from 200MeV < T < 1GeV. Our estimate for the unquenched result in $2+1$-flavor QCD has very similar features.

[1] A. Kumar et al., Phys. Rev. D 106, 034505 (2022).
[2] A. Majumder, Phys. Rev. C87 034905 (2013).

We study the interaction of leading jet partons in a strongly interacting quark-gluon plasma (sQGP) medium based on the effective dynamical quasi-particle model (DQPM). The DQPM describes the non-perturbative nature of the sQGP at finite temperature $T$ and baryon chemical potential ${\mu }_B$ based on a propagator representation of massive off-shell partons whose properties are adjusted to reproduce the lQCD EoS for the QGP in thermodynamic equilibrium. We present the results for the jet transport coefficients, i.e. the transverse momentum transfer squared per unit length $\hat{q}$ and the energy loss per unit length $\mathrm{\Delta }E=dE/dx$ in the QGP and investigate their dependence on the temperature $T$ and baryon chemical potential ${\mu }_B$ as well as on jet properties such as the leading jet parton momentum, mass, flavor, and the choice of the strong coupling constant. In this work both elastic and radiative scattering processes of leading jet parton with the sQGP partons are considered. We compute the cross sections and transport coefficients and compare the contributions from elastic partonic scattering and radiative processes for the emission of massive gluons. We present a comparison of our results for the elastic energy loss in the sQGP medium with pQCD results as well as with lattice QCD and also with estimates for $\hat{q}$ by the JET and JETSCAPE Collaborations based on a comparison of hydrodynamical calculations with experimental heavy-ion data.

In this work, by exploiting jet substructure techniques, we identify the transition from early-time perturbative splittings to late-time non-perturbative emissions and its associated timescale at both RHIC and LHC energies. We introduce three experimentally robust splittings along the jet clustering tree, each related to the perturbative, non-perturbative-like regions and the transition between them. The population of such splittings is quantified via a first phenomenological study of the formation time in a Monte Carlo model to highlight its sensitivities and discuss its experimental feasibility. Finally, we show how these timescales change in a scenario when jet quenching effects, induced by an extended Quark-Gluon Plasma, take place along the parton shower.

The heavy-ion collisions produce a hot, dense medium, and high-momentum partons from the collision traverse this medium while losing energy to it. This talk presents new measurements of the azimuthal dependence with respect to the event plane of single jet yields and high momentum charged particles yields in Pb+Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV. As the distance traversed by the partons in the medium is dependent on the angle with respect to the event plane at which the partons are produced, these measurements give insight into the path-length dependence of parton energy loss. The magnitude of angular modulation is quantified by the parameter $v_n$ with respect to the $n^{th}$ order event plane. In this talk we will present these two measurements that show $v_2$, $v_3$, and $v_4$ as a function of $p_T$ and collision centrality. In both measurements, a non-zero value of $v_2$ and $v_3$ are observed, suggesting that fluctuations in the initial state play a small but distinct role in jet energy loss. Both measurements explore a higher transverse momentum regime and higher-order harmonics than current measurements benefiting from the high statistics 2018 Pb+Pb heavy ion data recorded by ATLAS. These measurements provide new information about the path-length dependence of jet quenching.

The injection of energy and momentum from a jet into the QGP generates a wake, which leads to soft and semi-hard particle creation correlated with the jet direction after the QGP hadronizes. As several jet quenching studies have shown, this medium response phenomenon plays a crucial role in our understanding of many jet structure and substructure observables. Nevertheless, a detailed account of the phenomenological consequences of those wakes is still lacking, partly because of the computational complexity of current techniques used to describe their properties. In this work we present a computationally efficient description of the event-by-event, jet-by-jet, determination of the properties of the hadrons coming from QGP wakes. By making use of a single set of universal solutions obtained within linearized hydrodynamics on top of a Bjorken flow, and performing the adequate set of scalings, translations, rotations and boosts, we are able to match the results obtained (with much greater computational cost) using 3+1D hydrodynamics.

Measurements at RHIC and the LHC show strongly enhanced baryon-to-meson yield ratios at intermediate transverse momenta ($p_T$) in high-energy nuclear collisions compared to $p$+$p$ baseline. This enhancement is attributed to the following QGP effects: strong hydrodynamic flow and parton recombination. Jet probes have been used extensively to gain insights into QGP properties, with substantial modifications to jet yields and internal structures seen across multiple measurements. Despite apparent medium-induced changes to jet fragmentation patterns, LHC results indicate that in-jet particle production is significantly different from that of the QGP bulk. To explore this behavior at RHIC, we employ particle identification through time of flight and $dE/dx$ information alongside jet-track correlations to measure in-jet particle production for $p_T<5.0$ GeV/c. We present the first in-cone baryon-to-meson yield ratios associated with fully reconstructed jets from 200 GeV Au+Au and $p$+$p$ collisions using the STAR detector at RHIC.

PHENIX presents the simultaneous measurement of high pt (8-18 GeV/c) direct γ and π0 production in d+Au collisions at 200 GeV. The analysis is performed for different events samples selected by event activity. The direct γ-to-π0 ratio is independent of event activity, except for events with the highest activity where the ratio is slightly enhanced. Final state effects are expected to be small for direct photons and initial state effects are expected to be similar for direct γ and π0. Therefore, the new PHENIX results suggest that π0 production is suppression in the final state of the most central d+Au collisions. Expressed as nuclear modification factor RxA, this suppression is about 20%. Here RxA is determined in a model independent way, by quantifying the effective number of binary collisions from the ratio of direct photons measured in d+Au compared to p+p collisions. To establish if the suppression is linked to energy loss, PHENIX is currently analyzing p+Au and 3He+Au collisions. In this talk the latest results will be presented.

Relativistic heavy-ion beams at the LHC are accompanied by a large flux of equivalent photons, leading to multiple photon-induced processes. This talk presents searches for physics beyond the standard model enabled by photon-photon processes in both di-tau and di-photon final states. The tau-pair production measurements can constrain the tau lepton’s anomalous magnetic dipole moment (g-2), and a recent ATLAS measurement using muonic decays of tau leptons in association with electrons and tracks provides one of the most stringent limits available to date. Similarly, light-by-light scattering proceeds via loop diagrams, which can contain particles not yet directly observed. Thus, high statistics measurements of light-by-light scattering shown in this talk provide a precise and unique opportunity to investigate extensions of the Standard Model, such as the presence of axion-like particles.

Photons are emitted at all stages of relativistic heavy-ion collisions and do not interact with the medium strongly. With access to the versatility of RHIC, measurements of low momentum direct photons are made possible across different system size and beam energies. An excess of direct photons, above prompt photon production from hard scattering processes, is observed for a system size corresponding to $d{N}_{ch}/d\eta$ of 20-30, with a large azimuthal anisotropy and a characteristic dependence on collision centrality. After subtracting the prompt photon component, the inverse slope of the spectrum is continuously increasing with the effective temperature ranging from 250 MeV/c at $p_T$ of 1-2 GeV/c to about 400 MeV/c at 2-4 GeV/c. Within the experimental uncertainty, there is no indication of a system size dependence of the inverse slope. In this talk, results from Au+Au collisions from the PHENIX experiment will be presented.

Electroweak bosons produced in hard-scattering processes at the early stage of the collision, are efficient probes of the initial state of the collision. While the W measurements in pp collisions are a stringent test of perturbative QCD-based calculations and production mechanisms, they can constrain the nuclear parton distribution functions in p-Pb and Pb-Pb collisions.

Electroweak bosons are studied with ALICE in pp collisions at $\sqrt{s}$ = 13 TeV, p-Pb collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}$ = 8.16 TeV and Pb-Pb collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}$ = 5.02 TeV via their leptonic decays in the muon and electron channels at forward rapidity ($-4.0<\eta <-2.5$) and midrapidity ($|\eta |<0.8$), respectively. The observations in p-Pb and Pb-Pb collisions at forward rapidity give access to low Bjorken-$x$ values, a phase-space region poorly constrained by heavy-ion experiments.

The latest W-boson results concerning differential measurements of the normalised production yields, production cross sections, nuclear modification factors and lepton-charge asymmetry as a function of rapidity, transverse momentum, collision centrality and charged-particle multiplicity are presented. The production of W bosons in association with hadrons as a function of the charged-particle multiplicity in pp collisions is reported as well. Comparisons with model calculations are discussed.

Thermal photons are vital tool to study Quark-Gluon Plasma The photon production rate from the plasma at some temperature T is proportional to the transverse spectral function ${\rho }_T(\omega =|\overrightarrow{k}|,\overrightarrow{k})$. One can calculate the photon production rate also from the difference between ${\rho }_T(\omega ,\overrightarrow{k})$ (transverse) and ${\rho }_L(\omega ,\overrightarrow{k})$ (longitudinal) correlator as ${\rho }_L$ vanishes at the light cone. The UV part of ${\rho }_T-{\rho }_L$ is suppressed; therefore, the corresponding Euclidean correlator receives most of its contribution from the IR part of ${\rho }_T-{\rho }_L$. We also calculate the T-L correlator on $N_f=2+1$ flavor HISQ configurations with $m_l=m_s/5$ at temperature ∼1.15$T_c$ and 1.3 $T_c$. We have used two ansätze of the spectral function, which are 1) Polynomial ansatz of the spectral function connected to the UV region compatible with OPE expansion and 2) Hydro-inspired spectral function. We have also used the Backus-Gilbert method to estimate the spectral function. We will compare the photon production rate estimated from all these different methods.

The hadronization process is a well-known non-perturbative process, which is happening in both elementary collisions such as $p+p$, $e^{+}+e^{-}$ collisions, and also the relativistic heavy ion collisions. Studying the hadronization mechanism is crucial for understanding the QCD in low-energy regions.
In elementary collisions, the hadronization process is usually described by the fragmentation model, while the recombination plays an important role in quark hadronization in the hot medium, which created in relativistic heavy ion collisions. The state-of-art is mixing the fragmentation and recombination process. The recombination dominates in the low transverse momentum region while fragmentation takes over in the high transverse momentum region.
Due to the large mass, distinguishable, and traceable properties, heavy flavor supplies a unique probe to study the hadronization mechanism in heavy ion collisions.
We convened many theoretical groups to do the comparison of the hadronization models with given initial condition.
In this talk, we will present the differences and connections between different hadronization models.
We compare in detail the $H_{AA}$ yield and the elliptic flow $v_2$ of heavy flavor hadrons obtained in different theoretical models and point out how the different models influence the spectra. A summary will be given at the end of this talk.

In this contribution, we present the new measurements of non-prompt ${\mathrm{D}}^{+}$ and ${\mathrm{D}}_{\mathrm{s}}$ in pp collisions at $\sqrt{s}$ = 13 TeV. Together with the final measurements of non-prompt ${\mathrm{D}}^0$ and ${\mathrm{\Lambda }}_{\mathrm{c}}^{+}$, they are crucial to study the beauty quark hadronisation in proton-proton (pp) collisions and their difference with respect to ${\mathrm{e}}^{+}{\mathrm{e}}^{-}$ collisions. In addition, the baryon-to-meson ratio in pp collisions compared with that in ${\mathrm{e}}^{+}{\mathrm{e}}^{-}$ and electron--proton collisions and model predictions, and the measurements of charm fragmentation fraction in pp and pPb collision will be reported as well.

Furthermore, the new non-prompt ${\mathrm{\Lambda }}_{\mathrm{c}}^{+}/{\mathrm{D}}^0$ ratio in p-Pb collisions as well as the first measurement of non-prompt ${\mathrm{D}}^0$ nuclear modification factor $R_{\mathrm{pPb}}$ at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV will be presented. The status of prompt ${\mathrm{\Xi }}_{\mathrm{c}}$ $R_{\mathrm{pPb}}$ studies will be reported. They provide important information about Cold-Nuclear Matter (CNM) effects and to understand how the possible presence of collective effects could modify the production of heavy-flavour hadrons and the similarities observed among pp, p-nucleus, and nucleus--nucleus systems.

The total rate of heavy quark production can be calculated with perturbative QCD techniques. However, the fraction of heavy quarks that pair with a light quark (forming mesons) versus the fractions combine with two other quarks (baryons) baryons or 3 or more other quarks (exotic states) is sensitive to the nonperturbative hadronization process. LHCb is uniquely well suited to study such effects in the heavy quark sector, down to very low transverse momentum. Here we will present LHCb results on the production rates of ${\mathrm{\Lambda }}_b^0$ baryons and $B_s^0$ mesons relative to $B^0$ mesons, and $D_s^{+}$ relative to $D^{+}$ mesons versus multiplicity in $pp$ and $p$Pb collisions. Potential implications for the hadronization mechanism of heavy quarks and our understanding of the factorization of fragmentation functions will be discussed.

The surprising collectivity signal emerging in small hadronic systems for light and heavy quarks raises the question whether a quark-gluon plasma is created in those systems too. The conjectured QGP formation could also enhance baryon production because of coalescence processes. Moreover, strangeness enhancement signals have been observed. Recent measurements show charm baryon-to-meson ratios are enhanced in heavy ion collisions compared to pp collisions. In this talk, the studies of collectivity for charm and bottom mesons in pp and pPb collisions will be presented. New measurements of the multiplicity dependence of charm baryon-to-meson ratios will also be presented over a wide multiplicity range, and compared with those in the strangeness sector. These measurements provide new insights into the origin of heavy flavor hadron collectivity and charm hadronization.

The JETSCAPE Collaboration reports a new Bayesian Inference analysis of jet transport in the QGP, using both hadron and jet inclusive suppression data. The JETSCAPE framework comprises a modular multi-stage modeling of in-medium jet evolution and medium response, together with a statistical framework for rigorous data-model comparison using a Bayesian formalism. The multi-stage approach includes virtuality-dependent in-medium partonic energy loss coupled to a detailed dynamical model of QGP evolution. In this talk we present a new JETSCAPE Bayesian inference analysis that extends the previously published JETSCAPE Bayesian determination of $\hat{q}$, which was based solely on inclusive hadron suppression data. It now incorporates inclusive jet measurements at RHIC and the LHC as well. We explore tension between different datasets considered in the analysis, and report a new, multi-messenger, determination of $\hat{q}$. This study represents the next step in the program toward a comprehensive study of the constraints of the QGP properties from jet quenching data. Future possibilities, including more sophisticated modeling and the inclusion of other types of measurements, will also be discussed.

In studies of the QGP, it has been observed that in high-energy heavy-ion (A+A) collisions, high-momentum hadrons and heavy flavor electrons are suppressed, indicating that QGP is strongly coupled, and that quarks lose energy as they traverse the medium. In order to quantitatively discuss this important energy loss mechanism, for charged hadrons consisting of light quarks, in addition to the conventional fractional momentum losses (Sloss), which uses the comparison with p+p, the angle-dependent fractional momentum losses (S'loss) at different emission angles using azimuthal anisotropy ($v_2$) are measured at $\sqrt{s_{NN}}$ = 200 GeV. We will report the detailed and new path-length dependent functions obtained from these measurements.
We will also discuss the latest heavy quark measurements in PHENIX for a comprehensive understanding of the energy loss mechanism. Like light quarks, heavy quarks lose energy when interacting with the QGP. The gluon bremsstrahlung by heavy quarks is expected to be suppressed at small angles due to the dead cone effect, and thus the energy loss is expected to be quark-mass-dependent. PHENIX silicon detectors are able to separate single electrons from charm and bottom decays by utilizing the difference of their decay lengths. In this talk, we will report the latest results of heavy flavor productions and their nuclear modifications as a function of $p_T$ and centrality, and discuss the energy loss mechanisms in QGP.

The microscopic production mechanism of light (anti)nuclei in high-energy hadronic collisions is still mysterious and is a highly debated topic in the scientific community. Two different phenomenological models are typically used to describe the experimental data: the statistical hadronization model and baryon coalescence. In the former, light nuclei are emitted from a source in local thermal and hadrochemical equilibrium. Their yields are calculated using the QCD partition function by imposing the conservation of quantum numbers inside the so-called correlation volume. In the coalescence approach, light nuclei can be formed if the phase-space configuration of nucleons at kinetic freezeout is compatible with the Wigner density of the bound state. A straightforward prediction of the coalescence model is an enhanced coalescence probability of nuclei inside jets compared to that in the underlying event, measured in small collision systems.

In this contribution, the $p_{\mathrm{T}}$-differential production yields and coalescence probabilities of (anti)deuterons inside jets and in the underlying event measured by ALICE in small collision systems are presented. These results are compared to expectations from coalescence and a reaction-based model. In the latter approach, implemented in the PYTHIA 8.3 event generator, deuterons are generated using ordinary nuclear reactions.

Two-particle jet-like angular correlations with identified strange hadrons allow the measurements of both jet and non-jet components of strange particle production, and in this way to investigate the extent to which the strangeness enhancement observed in small collision systems is a result of soft (medium-like) or hard (jet-like) processes. Relative contributions of these processes to strangeness production mechanisms can be probed by examining changes in the strange hadron over non-strange hadron ratios within jets and in the underlying event separately. In addition, changes to the jet hadrochemistry are studied by measuring strangeness production in the away-side jet.

In this talk, we present the first measurements of the $\varphi$/h, $(\mathrm{\Lambda }+\bar{\mathrm{\Lambda }})$/h and ${\mathrm{K}}_{\mathrm{S}}^0$/(${\pi }^{+}+{\pi }^{-}$), $(\mathrm{\Lambda }+\bar{\mathrm{\Lambda }})$/(${\pi }^{+}+{\pi }^{-}$) ratios in jets and underlying event as a function of charged-particle multiplicity using jet-like di-hadron angular correlations in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$= 5.02 TeV and pp collisions at $\sqrt{s}$= 13 TeV measured with ALICE. The results suggest that the strangeness enhancement originates in the underlying event.

Understanding the modification of jets and high-$p_T$ probes in small systems requires the integration of soft and hard physics. We present recent developments in extending the JETSCAPE framework to build an event generator, which includes correlations between soft and hard partons, to study jet observables in small systems. The multi-scale physics of the collision is separated into different stages. Hard scatterings are first sampled at binary collision positions provided by the Glauber geometry. They are then propagated backward in space-time following an initial-state shower to obtain the initiating partons’ energies and momenta before the collision. These energies and momenta are then subtracted from the incoming colliding nucleons for soft-particle production, modeled by the 3D-Glauber + hydrodynamics + hadronic transport framework.This new hybrid approach includes non-trivial correlations between jet and soft particle productions in small systems. We calibrate this framework with the measured event activity distributions in p+p and p+Pb collisions at 5.02 TeV. We further compare our results for final state hadron’s $p_T$-spectra from low to high $p_T$ in p+p and p+Pb collisions with experimental results in p+Pb at the LHC. Lastly, we present results of additional observables such as the distributions of jet recoiling from a high-$p_T$ hadron and the nuclear modification factor $R_{pPb}$ as a function of event activity.

We employ machine learning techniques to identify important features that distinguish jets produced in heavy-ion collisions from jets produced in proton-proton collisions [1]. We formulate the problem using binary classification and focus on leveraging machine learning in ways that inform theoretical calculations of jet modification: (i) we quantify the information content in terms of Infrared Collinear (IRC)-safety and in terms of hard vs. soft emissions, (ii) we identify optimally discriminating observables that are analytically tractable, and (iii) we assess the information loss due to the heavy-ion underlying event and background subtraction algorithms. We illustrate our methodology using Monte Carlo event generators, where we find that important information about jet quenching is contained not only in hard splittings but also in soft emissions and IRC-unsafe physics inside the jet. This information appears to be significantly reduced by the presence of the underlying event. We discuss the implications of this for the prospect of using jet quenching to extract properties of the QGP. Since the training labels are exactly known, this methodology can be used directly on experimental data without reliance on modeling. We outline a proposal for how such an experimental analysis can be carried out, and how it can guide future measurements.

[1] Lai, Mulligan, Ploskon, Ringer [JHEP 10 (2022) 011]

In recent years jet substructure observables have been used at the LHC as instruments to search for new physics and test perturbative and non-perturbative processes in QCD. In heavy-ion collisions, these jet substructure observables can additionally elucidate the production and evolution of the QCD medium. The jet mass is one such observable that probes the momentum transfer scale of the initial hard scattering. Additionally, the generalized jet angularities summarize the jet substructure using two continuous parameters which differentially weight the jet constituents’ relative angle and $p_{\mathrm{T}}$. One jet angularity configuration, the jet thrust, has been compared to the jet mass and has shown surprising differences in comparison with models. ALICE has performed a new measurement for both observables using an identical jet sample to study this difference more closely. The ALICE tracking system's high-precision capability provides a unique opportunity at LHC energies to measure jets at lower $p_{\mathrm{T}}$. We report the generalized jet mass and jet angularities using charged-particle tracks in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV with ALICE. Various jet angularity parameters are investigated for the jet resolution parameter R = 0.2. Results are compared to pp collisions and theoretical models.

We present a new model for jet quenching from coherent radiation in a brick medium. The jet energy loss is simulated as a perturbative final-state vacuum parton shower followed by a medium-induced shower originating from elastic and radiative collisions with the medium constituents. Coherency is achieved by starting with trial gluons that acts as field dressing of the initial jet parton. These are formed according to a Gunion-Bertsch seed. The QCD version of the LPM effect is attained by increasing the phase of the trial gluons through elastic scatterings with the medium. Above a phase threshold, the trial gluon will be realised and can produce coherent radiation themselves.

The model has been implemented in a Monte Carlo code and has been validated by successfully reproducing the BDMPS-Z prediction for the energy spectrum. The realistic case with minimal assumptions are also produced and shown. In particular, we show the influence of various parameters on the energy spectrum and transverse momentum distribution, such as the in-medium quark masses, the energy transfer in the recoil process, and the phase accumulation criteria, especially for low and intermediate energy gluons.

Future studies will allow for the interface with full simulations of the quark-gluon-plasma with hydrodynamic evolution, such as vHLLE, along with subsequent hadronisation of the jet partons in order to produce realistic distributions that can be directly compared to LHC and RHIC data.

Modifications of the internal structure of jets through interactions with the QGP produced in heavy-ion collisions, referred to as jet quenching, are used to study the properties of the QGP. In this talk, we present the first measurement of the angle between pairs of jet axes, $\mathrm{\Delta }{R}_{\mathrm{a}\mathrm{x}\mathrm{i}\mathrm{s}}$, in central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV with ALICE. We compare this novel jet substructure measurement to a selection of jet quenching models. The data favor models implementing incoherent energy loss of jet constituents in the QGP, but also agree with models invoking an enhancement of quark-initiated jets. On the other hand, our measurement disfavors the intra-jet in-medium $p_{\mathrm{T}}$ broadening from the BDMPS formalism. Moreover, to comprehensively study the perturbative and non-perturbative aspects of jet structure, we measured the energy-energy correlators (EEC) that emphasize the angular structure of the energy flow within jets. Defined as the energy-weighted cross section of particle pairs inside jets, the scaling behavior of the EECs as a function of pair distance exposes a distinct separation of the perturbative from the non-perturbative regime, revealing parton-type dependent dynamics of jet formation and their confinement into hadrons. In this talk, we present a new measurement of EEC in pp collisions at the LHC and compare it with pQCD predictions. This measurement serves as a baseline for future measurements in heavy-ion collisions.

Ultra-peripheral collisions (UPC) of heavy nuclei provide the opportunity to study interactions between high energy photons induced from the electromagnetic field of ultrarelativistic nuclei and the nuclei from the other beam. The photon fluctuates to a quark-antiquark dipole which then elastically scatters off the nucleus, emerging as vector meson and opposite-charge pseudoscalar meson pair.

The excellent particle identification capabilities of ALICE enable the study of photoproduced ${\pi }^{+}{\pi }^{-}$ pairs and $K^{+}{K}^{-}$ pairs at midrapidity in Pb--Pb collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}$ = 5.02 TeV. We will present an analysis of the ${\rho }^0$ meson and direct ${\pi }^{+}{\pi }^{-}$ photoproduction exhibiting the interference, obtained from a fit to the invariant mass spectrum of ${\pi }^{+}{\pi }^{-}$ pairs. In addition, we will present the prospects of studying the photoproduction of direct $K^{+}{K}^{-}$ pairs in UPCs.

Photonuclear interactions are studied in ultra-peripheral p-Pb collisions with the ALICE experiment, where the photon radiated by a Pb nucleus probes the gluon density of the proton at low Bjorken-x. The exclusive $\mathrm{J}/\psi$ photoproduction cross section $\sigma (\gamma +\mathrm{p}\to \mathrm{J}/\psi +\mathrm{p})$ is expected to follow a power law trend as $x$ decreases, but it should deviate from this trend at low $x$ due to gluon saturation. In addition, gluon saturation effects are also expected to be visible when studying the dissociative $\mathrm{J}/\psi$ photoproduction cross section $\sigma (\gamma +\mathrm{p}\to \mathrm{J}/\psi +\mathrm{X})$ because of reduced quantum fluctuations of the substructure of the proton in the saturation regime. The ALICE collaboration has measured both processes. In this talk, the first measurement of the dissociative $\mathrm{J}/\psi$ photoproduction at the LHC will be presented. Finally, we will present the study of dimuon events produced in two-photon interactions. First results for low-mass dimuons will be discussed. Such measurements complement the studies of $\mathrm{J}/\psi$ photoproduction and contribute to a better understanding of the photon fluxes generated by the lead nucleus.

The classical field approximation to Color Glass Condensate for two colliding nuclei has been solved in the literature using numerical methods and recursive analytic solution. In the weak field limit, analytic solutions in transverse momentum space have also been known for some time. Based on the latter, we derive expressions for the space-time dependence of classical gluon 2-point functions $⟨F^{\mu \nu }(x^{\alpha })F^{\kappa \lambda }(y^{\beta })⟩$ in the weak-field limit. For the McLerran-Venugopalan (MV) model, in many cases these expressions are shown to lead to solutions in closed analytic forms valid at all times. We also propose an alternative model which maintains UV-regularity by accounting for local correlations between color charges in the transverse plane. The new model allows for a straight forward calculation of the time dependence of the gluon energy momentum tensor and angular momentum density in early nuclear collisions in the weak field limit. We also discuss the initial motion of the nuclei after the collision.

We developed a formalism to study momentum anisotropy, in particular, the collective flow $v_2$, in the ultra-relativistic onium-onium scattering. We derived the impact-parameter dependent cross section up to the next-to-leading order in the eikonal approximation. With this formalism, we are able to interpret the origin and behavior of $v_2$ in the dilute limit, by investigating the elementary dipole-dipole scattering, $q\overline{q}+q\overline{q}\to g+X$. We calculated $v_2$ in the $\pi +\pi \to g+X$ process at a comprehensive coverage of impact parameter and transverse momentum. The valence sector light-front wave function of the $\pi$ is obtained numerically from the Basis Light-Front Quantization, a non-perturbative light-front Hamiltonian approach, in a holographic basis. For comparison and as a complementary study, we also calculated $v_2$ in the $J/\psi +J/\psi \to g+X$ process. The $J/\psi$ light-front wavefunction is built analytically from the phenomenological framework of Small-basis Light-Front Wavefunction. With this work, we have shown that momentum anisotropy can develop due to the interference of the valence quarks. This formalism is generic and can be applied to other hadrons and photons in the future.

During the last years, there has been an increasing interest in how the quark mass affects the jet quenching phenomena and dynamics of heavy flavor in HIC. Here, we will present a new effect, which consists in anisotropic broadening and gluon radiation sourced by the background flow, transverse to the parton momentum, and sensitive to the quark mass. This effect appears due to a modification of the scattering potential in evolving matter, and scales as second power of mass over the parton energy. We will also discuss how this mass ordered anisotropy affects the overall heavy flavor directionality in HIC and its possible effect in the observed harmonic coefficients from the corresponding momentum anisotropy in both small and large systems.

Correlation functions of energy flow operators have been recently proposed as a tool to identify the onset of colour coherence within the jets. As a promising exploration avenue to unveil the scales of the Quark-Gluon Plasma, it has yet to be demonstrated how the medium back-reaction to the jet propagation will blur such identification. In this work, by using a perturbative prescription to describe the jet-medium interactions and its re-scatterings, we show which weight of the normalised two-point correlator can maximise the separation between the wide range of momentum scales that go into the development of an in-medium jet: in-medium radiation and medium-recoiling particles. Additionally, we also explore the energy correlators' sensitivity to the different medium response momentum scales and their thermalization.

Recent measurements by the CMS and ATLAS experiments reveal a deficit of charged particles in pp collisions with excited Υ(nS) states compared to the Υ(1S) ground state. This observation is suggested to be a manifestation of excited bottomonia suppression in pp interactions. The analysis presented in this talk is an independent approach, complementary to the CMS and ATLAS analyses, based on first physics principles that finds a significant suppression in the production of excited bottomonia states in pp collisions at the LHC energies. The analysis uses transverse mass scaling as an empirical tool to quantify the magnitude of the suppression. Based on the analysis of shapes of momentum distributions, one can conclude that the Y(2S) production in pp collisions is suppressed by a factor of approximately 1.6 and Υ(3S) by a factor of approximately 2.4 from what would be expected from the momentum distribution of Y(1S). Details of the analysis and striking parallels to the findings of ATLAS and CMS experiments would help shed light on the nature of quarkonia production in pp collisions.

Based on https://arxiv.org/abs/2203.11831

This project aims the application of non-extensive statistics, more specifically that proposed by C. Tsallis, in the study of the transverse momentum distribution of mesons composed of charm quarks produced in collisions between heavy ions at relativistic energies. Non-extensive statistics has been very successful in the description of transverse momentum spectra of particles produced in hadronic collisions at high energies, whose interpretation of the non-extensive parameter q has been widely discussed. The success of this description might be connected to the degree of equilibrium reached in these collisions, an important condition for a broad understanding of its dynamics. This question is particularly important for heavy quarks in collisions between heavy ions, given its unique character in the investigation of the medium formed in these collisions. We will present some results of a systematic study of charm meson transverse momentum distributions fits, mainly the relative behavior of the temperature and q parameter for different particles and collision centralities, searching for an interpretation for the obtained results regarding the dynamics of charm quarks in these collisions.

Particle correlations are a powerful tool to study the bulk properties in relativistic heavy ion collisions. The momentum correlations between identical particles originating from the same particle-emitting source, referred to as the Bose-Einstein correlations, measure scales that are related to the geometrical size of the source. The two particle azimuthal angular correlations measure the momentum spatial anisotropy of produced particles, providing information on collective phenomena arising in the dense nuclear medium. This poster will discuss new LHCb measurements of Bose-Einstein correlations and collective flow coefficients in $p$Pb and PbPb collisions in the forward rapidity region.

Distinguishing between the modification of quark- and gluon-initiated jets in the quark-gluon plasma (QGP) remains an unresolved challenge without a definitive answer from experiment. We demonstrate that a fully data-driven technique, known as topic modeling, may be used to study the separate modification of quark and gluon jets experimentally. Our proof-of-concept study is based on proton-proton and heavy-ion collision events from the Pyquen generator with statistics accessible in Run 4 of the Large Hadron Collider. We use topic modeling to extract the separate modification of quark and gluon jet substructure in the QGP. We show that this data-driven technique is robust to large backgrounds in heavy-ion collisions by smearing our input distributions and obtaining similar results. These results suggest the potential for an experimental determination of quark and gluon jet substructure and their modification.

The measurement of the dijet production cross-section in p+Pb collisions is of great interest to the understanding of initial state effects. The analysis of this channel can provide input to the parameterization of the modification of parton distribution functions (PDFs) in nuclei and to search for the onset of non-linear QCD effects or gluon saturation at low Bjorken-x. In 2016, the ATLAS experiment at the LHC collected 164 nb${}^{-1}$ of data from p+Pb collisions at the center-of-mass energy of 8.16 TeV. This poster presents ATLAS preliminary results for the triple-differential inclusive dijet cross-section in p+Pb. The results of this measurement can be used to constrain nuclear PDFs over a broad kinematic range. The events characterized by at least one jet in the forward region are also analyzed as a function of centrality to compare the dijet production in central and peripheral collisions and search for evidence of gluon saturation.

We present calculations of dielectron anisotropic flow in heavy-ion collisions at HADES beam energies from a hadronic transport approach. The collectivity of the electromagnetic radiation produced during the evolution of these collisions has recently been dubbed as a barometer, serving as a probe for the flow velocity of the underlying hadronic matter. In particular, we study the elliptic flow coefficient $v_2$ of dileptons in different collisions systems, and its relation to the flow of hadrons.

Keywords : Heavy-ion Collisions, Event generator, EPOS, PHSD, EPOSi+PHSDe, Quark-Gluon
Plasma

Ultrarelativistic heavy-ion collisions at RHIC and the LHC provide a hot and ultra-dense form of matter composed of deconfined quarks and gluons, named QGP. Different models like EPOS and PHSD allow to study the space-time evolution of such heavy-ion collisions. Their dynamics is complicated; hence, various stages should be considered. The first is the primary scattering which defines to a large extent the matter distribution in the phase-space. The second stage concerns the evolution of the partonic system until the system is sufficiently dilute to hadronize. The EPOSi+PHSDe approach is introduced in this thesis, in which the EPOS model is used to determine the initial distribution of matter (partons/hadrons). This part is referred to as EPOSi. Then PHSD is employed to simulate the evolution of the matter in a non-equilibrium transport approach, referred to as PHSDe. The coupling of the two approaches is non-trivial and not straight-forward. Comparing the three models, EPOS, EPOSi+PHSDe, and PHSD, interesting results find concerning their respective space-time evolutions. The results demonstrate considerably different behavior in terms of radial expansion, especially asymmetric expansion, indicating that these three models will provide different results concerning key observables ( pT/mT spectra, y/ƞ distribution, v2/3/4) for Au-Au collisions at 200 GeV/A.

The electromagnetic fields produced by non-central heavy ion collisions are extremely powerful and give rise to a plethora of fascinating subjects in the strongly interacting matter. Their evolution is a significant and unresolved issue.
In this talk, firstly, I will show the electromagnetic evolution in the pre-equilibrium stages which is a gluon-dominated and far-from-equilibrium system after the collisions. Quarks and antiquarks will be produced gradually via inelastic collisions. We find the induced magnetic field is very weak in this stage due to the lacking of quarks.
Next, I will present the new effect we proposed which is called the incomplete electromagnetic response of hot QCD matter.
We examine the validity of Ohm's law and find that the induced electric current increases from zero and relaxes towards the value from Ohm's law. The lower-than-expected electric current significantly suppresses the induced magnetic field and makes the electromagnetic response incomplete. And leads to a strong suppression of the magnetic field.
Considering both these two effects, the magnetic field will decay faster in heavy ion collisions, and which magnitude is much weaker than expected.
Finally, I will show our study on the charmonium dissociation under electromagnetic fields, which can be a sensitive probe for detecting the short-lived electromagnetic fields in heavy-ion collisions.

The hotspot model has proven to be an efficient tool to study coherent and incoherent diffraction HERA data by modelling the initial state fluctuations of the gluon density of the proton. The hotspot model in its original form is a non-perturbative model applicable for low momentum transfer and underestimates the incoherent cross section in orders of magnitude when extended for large momentum transfer studies for J/ψ photo-production at HERA. We present here a model of hotspot splittings based on the resolution for the evolution of initial state fluctuations in the hotspot model inspired by the DGLAP parton shower approach This is reliable as both the Bjorken limit and the incoherent diffraction at large momentum transfer probes the gluon wave function at smaller length scales as we increase the resolution. In addition to the geometrical fluctuations, we have additional sources of fluctuations in our model namely the hotspot width, number, and normalisation fluctuations which leads to a good agreement of our model’s prediction with data. In the framework developed, we obtain a good description of both the normalization and shape of coherent and incoherent differential cross sections (t-spectrum) simultaneously.

Bayesian inference provides a powerful approach to constrain jet quenching model parameters using experimental measurements. It remains an open question, however, which jet observables provide complementary information in this approach, and in turn which observables the community should focus on measuring and calculating. In this talk we report a first, exploratory study which incorporates jet substructure observables in a Bayesian inference analysis of jet quenching, based on the JETSCAPE framework. We examine the additional information that jet substructure observables provide beyond that contained in inclusive jet and hadron suppression observables. We discuss the implications of these findings on the future experimental and theoretical jet quenching programs, including both opportunities and limitations offered by jet substructure observables.

In this work, we assess the impact of the expansion of the medium on angular distribution of gluons at different kinematical scales in a medium-induced cascade . Firstly, we study the scaling of the gluon spectra at low$-x$ between expanding and static medium profiles and apply them to obtain the transverse momentum broadened spectra. The numerical solutions for the in-medium cascades are obtained from the gluon evolution equations using the Monte Carlo event generator MINCAS. Additionally, we investigate the early and late onset of the initial quenching time for the Bjorken expanding profile. Next, we study the angular distributions for the in-cone radiation for different media and observe that the out-of-cone energy loss proceeds via the radiative break-up of hard fragments followed by an angular broadening of soft fragments. We note that for an effective in-medium path length, the angular distributions for soft fragments are very similar for different media. Also, harder jet fragments within the jets inside a cone are more sensitive to the details of the medium expansion as compared to softer fragments which are responsible for most of the gluon multiplicity in the cascade. Finally, we observe that cascades in the expanding media are relatively more collimated than in a static media and discuss phenomenological implications of our results on jet quenching observables.

In the context of jet-medium interaction, we consider the response of QCD-like plasma to energy/momentum disturbance as a function of the gradient. For both N=4 super-Yang Mills theory in strong coupling limit and kinetic theory under relaxation time approximation, we find that hydrodynamic modes continue dominating medium's response even in the region where Knudsen number is large. However, in this extended hydrodynamic regime, both the first-order and second-order hydrodynamics fail to characterize medium's behavior. We construct a simple yet not trivial extension of the Muller-Israel-Stewart theory, namely MIS, and show this novel framework can quantitatively describe hydrodynamic modes in both hydrodynamic and extended hydrodynamic regimes with a suitable choice of model parameters for representative microscopic theories with and without quasi-particle descriptions.We apply MIS to study how a Bjorken-expanding QGP responds to a moving energetic parton.

[1] Weiyao Ke and Yi Yin, 2208.01046 .

Heavy quarks, like charm quarks, are produced early in the relativistic heavy-ion collisions and probe all stages of the evolution of the created medium – the Quark Gluons Plasma. Two-particle correlations at low relative momentum (the femtoscopic correlations) are sensitive to the interactions in the final state and the extent of the region from which correlated particles are emitted (so-called region of homogeneity). A study of such correlations between charmed mesons and identified hadrons could shed light on their interactions in the hadronic phase and interaction of charm quarks with the bulk partons.

We will present a study of femtoscopic correlations of $D^0$-$\pi$, $D^0$-$K$, $D^0$-proton pairs at mid-rapidity in Au+Au collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}$ = 200 GeV using data taken in the year 2014 by the STAR experiment. $D^0$ mesons are reconstructed via the $K^{-}$-${\pi }^{+}$ decay channel using topological criteria enabled by the excellent track pointing resolution provided by the Heavy Flavor Tracker. We will present the femtoscopic correlation function for $D^0$ transverse momentum $p_{\mathrm{T}}>1$ GeV/c in the 0-80% centrality.

The LHCb experiment has recently undergone a series of major upgrades: the entire tracking system has been replaced with higher-granularity sensors, the readout electronics have been upgraded, and all hardware triggers have been replaced with a new state-of-the-art streaming readout system. In addition, the gaseous target SMOG system has been upgraded with a dedicated storage cell to greatly increase the rate of fixed target collisions at LHCb. This talk will include the first performance results from the new LHCb tracking system, the streaming readout system, and SMOG II, with a focus on how these upgrades directly impact the LHCb heavy ion physics program. Further upgrades planned for LHC Run 4 and 5 will also be discussed.

The ALICE experiment has been upgraded over the last years during the LHC Long Shutdown 2.
With the new and upgraded detectors ALICE is now capable of reading out the data of the collisions in a continuous way. With a data acquisition rate 100 times larger than before, an integrated luminosity of more than 10 nb${}^{-1}$ is expected to be collected for Pb--Pb collisions during the Run 3 (2022-2025) and Run 4 (2029-2032) data taking periods. In these heavy-ion collisions, we produce a quark-gluon plasma which radiates virtual thermal photons which mainly decay into dielectrons (electron-positron pairs).
Since dielectrons do not interact strongly, they are excellent probes of the hot, strongly-interacting matter produced in heavy-ion collisions. Not only the improved readout of the detectors but also the reduced material budget, as well as the improved pointing resolution of the detectors, are crucial for the dielectron analysis. They will help controlling the background from photon conversions and heavy-flavor hadron decays within the dielectron spectra.

This poster will give an overview of the first performance studies for dielectron analyses with the ALICE experiment based on Run 3 data. It will summarize the techniques used to track, identify and select electrons and positrons. Furthermore, first results of the dielectron spectra and their corresponding signal-to-background ratios and significances will be presented together with a comparison to the results in Run 2.

Constraining the initial condition of the QGP using experimental observables is one of the most important challenges in our field. Recent studies show that the Pearson Correlation Coefficient (PCC) between $v_n$ and event-wise mean transverse momentum $[p_{\mathrm{T}}]$, ${\rho }_n(v_n,[p_{\mathrm{T}}])$, and $[p_{\mathrm{T}}]$ fluctuations can probe several ingredients of the initial state. This talk presents precision measurements of $v_n-[p_{\mathrm{T}}]$ correlation for n=2,3 and 4 and high order $[p_{\mathrm{T}}]$ fluctuations in ${}^{129}$Xe+${}^{129}$Xe and ${}^{208}$Pb+${}^{208}$Pb collisions, and they are found to be small in the mid-central and central collisions in these systems. The ${\rho }_n$ and variance and skewness of $[p_{\mathrm{T}}]$ fluctuations show non-monotonic dependence on centrality, $p_{\mathrm{T}}$ and $\eta$. It was also found that the result depends on the centrality estimator used in the analysis, indicating a strong influence of volume fluctuations. In central collisions, where models generally show good agreement, the $v_2$--$[p_{\mathrm{T}}]$ correlations are sensitive to the triaxiality of the quadrupole deformation. A comparison of the model with the Pb+Pb and Xe+Xe data confirms that the ${}^{129}$Xe nucleus is a highly deformed triaxial ellipsoid that has neither a prolate nor oblate shape. This provides strong evidence for a triaxial deformation of the ${}^{129}$Xe nucleus from high-energy heavy-ion collisions.

Measurements of jet substructure in ultra-relativistic heavy ion collisions suggest that the jet showering process is modified by the interaction with quark gluon plasma. Modifications of the hard substructure of jets can be explored with modern data-driven techniques. In this study, a machine learning approach to the identification of quenched jets is designed. Jet showering processes are simulated with a jet quenching model Jewel and a non-quenching model Pythia 8. Sequential substructure variables are extracted from the jet clustering history following an angular-ordered sequence and are used in the training of a neural network built on top of a long short-term memory network. We show that this approach successfully identifies the quenching effect in the presence of the large uncorrelated background of soft particles created in heavy ion collisions.

based on arXiv: 2206.01628

We have studied the influence of realistic modeling of the medium formed in
Relativistic Heavy-Ion collisions on Jet Quenching phenomena. We used JEWEL to
simulate the medium modified parton shower and coupled it with vUSP-hydro$+{\mathrm{T}}_{\mathrm{R}}\mathrm{E}\mathrm{N}\mathrm{T}\mathrm{o}$ models. We have studied the influence of these combination of models on jet observables
such as $R_{AA}$, jet mass, $x_J$ and subjet fragmentation. We have
benchmarked our method with some of these observables and observed significant
differences in these observables behavior when a realistic hydrodynamics is used on them.

Understanding the apparent absence of the modification of high-$p_T$ partons in small colliding systems has become critical. A major avenue of investigation that remains largely unexplored is the identification of observables that are experimentally more robust in small colliding systems than the traditional $R_{AA}$. In recent years the study of jet substructure observables in heavy-ion collisions has accelerated and we now have at our disposal several promising observables that merit investigation in small systems. In order to facilitate the process of comparing analytically viable observables with existing and future experimental results, we have developed a plugin for JEWEL (Jet Evolution With Energy Loss) that allows the user to pass hydrodynamic profiles from any collision system to JEWEL. Code suitable for use with (2+1)D temperature and fluid velocity profiles, fully compatible with the newest available version of JEWEL will be made available publicly, as well as simple RIVET analyses. We briefly detail the particularly careful treatment of the local fluid velocity, and present several jet substructure observables in a variety of collision systems.

Heavy flavor jets are powerful tools to gain insight into the in-medium partonic energy loss mechanisms and the transport properties of the quark-gluon plasma (QGP) in high-energy nuclear collisions. In this work, we present the first theoretical study of the longitudinal momentum fraction $z_{||}$ carried by ${\mathrm{D}}^0$ meson in jets in Pb+Pb collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}$ = 5.02 TeV. The p+p baseline is provided by POWHEG+PYTHIA8 which matches the next-to-leading order hard processes with the parton shower. The in-medium evolution of heavy quark jets is employed by a Monte Carlo transport model which takes into account the collsional and radiative partonic energy loss in the expanding QGP. We observe steeper $z_{||}$ distributions of ${\mathrm{B}}^0$-jet compared to that of ${\mathrm{D}}^0$-jet at the same kinematics region in p+p collisions, which may be a hint of the harder jet fragmentation function of b-jet compared to c-jet in vacuum. In A+A collisions, it is shown that the jet quenching effect would in general decrease the values of $z_{||}$. In addition, we predict visibly stronger nuclear modifications of ${\mathrm{B}}^0$-jet $z_{||}$ distributions compared to ${\mathrm{D}}^0$-jet within the same $p_{\mathrm{T}}$ windows, as a result of the much steeper initial $z_{||}$ distribution of ${\mathrm{B}}^0$-jet in vacuum.

The ALICE experiment at the LHC investigates the properties of the hot and dense nuclear matter created in heavy-ion collisions. By comparing the particle production in pp and p--Pb collisions, possible nuclear initial state effects can be isolated. Measurements of the $\omega$ meson $p_{\text{T}}$-spectra in pp and p--Pb collisions not only allow for a determination of the nuclear modification factor $R_{\text{pA}}$, but also provide insights into the fragmentation process and serve as vital input for direct photon cocktail simulations.

The $\omega$ mesons can be reconstructed in ALICE via their primary decay channel into three pions ($\omega \to {\pi }^{+}{\pi }^{-}{\pi }^0$). While the two charged pions are being directly identified by the tracking detectors, i.e. the Time Projection Chamber and the Inner Tracking System, the ${\pi }^0$ is reconstructed from its two decay photons. These photons can either be detected in the calorimeters or via tracks in case they convert to an electron-positron pair in the detector material.

In this poster, the measurement of the $\omega$ meson production in pp and p--Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$TeV will be presented. This includes the signal extraction and various corrections of the $\omega$ meson yields, as well as comparisons to theory calculations.

Measurements of neutral mesons in small collision systems can serve as a baseline to understand modifications in heavy-ion collisions, where a QGP is formed.
These measurements can also be used to test pQCD predictions and to constrain fragmentation functions as well as parton distribution functions.
Furthermore, a precise knowledge of the $\omega$-meson production improves the measurement of direct photons, as photons produced in $\omega$ meson decays represent the third largest contribution of decay photon background.

This poster presents the invariant cross section of the $\omega$-meson in pp collisions at a center-of-mass energy of $\sqrt{s}=13$TeV measured by ALICE via its dominant decay channel $\omega \to {\pi }^{+}{\pi }^{-}{\pi }^0$.
While charged pions can directly be measured by the ALICE central barrel tracking detectors, neutral pions are reconstructed using their decay channel into two photons.
This reconstruction is realized with several complementary methods using the ALICE calorimeters as well as the central barrel tracking detectors.
The combined result covers an unprecedented $p_T$ range with competitive statistical and systematic uncertainties.

Recent results of charmed baryon production in $pp$ collisions showed a significant enhancement of the baryon-to-meson ratio compared with the expectation based on $e^{+}{e}^{-}$ collisions. This indicates that the charm fragmentation into hadrons is not an universal process among different collision systems, and different mechanisms may play a role in the hadronic collisions with respect to $e^{+}{e}^{-}$ collisions. Therefore, the measurements of charmed baryon production are crucial to investigate the hadronisation mechanism of charm quarks. The production yield measurement of the ${\mathrm{\Xi }}_c^0$ baryon has been measured in $pp$ collisions at $\sqrt{s}=$ 5 and 13 TeV. Further studies of the multiplicity dependence of the baryon-to-meson yield ratios can provide more information on how the charm hadronisation processes evolve from small to large collision systems. Measurements in $p$-Pb collisions are important to separate the cold nuclear matter effects from the effects associated with the formation of quark-gluon plasma. In this contribution, the most recent measurements of the ${\mathrm{\Xi }}_c^0$ production via the semileptonic decay channel ${\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{e}^{+}{\nu }_e$ in $pp$ collisions and the analysis status for the study of multiplicity dependence in $pp$ and $p$-Pb collisions will be shown.

Jets can be copiously produced in heavy-ion collisions at the LHC energies. Their calibration is crucial for precise measurements of various processes, such as top-quark pair production. The poster presents the measurement of jet energy scale and resolution in proton-lead collisions collected at 8.16 TeV in 2016. The balance between Z boson and jet transverse momenta is explored for jet $p_{\mathrm{T}}>20\mathrm{GeV}$ and $|\eta |<2.5$ to estimate jet performance in both data and simulation. The performance of two jet definitions, referred to as EMPFlow and HIJets, is studied and results are compared including systematic uncertainties. The presented results are a key input to the ongoing analysis of top-quark pair production in p+Pb collisions.

The precise measurement of the neutral meson production in pp collisions can be used to constrain fragmentation functions and parton density functions needed by pQCD calculations. Additionally, those measurements serve as input for direct photon analyses.
Moreover, the dependence of the neutral meson cross section on the event charged-particle multiplicity could give further insight into possible final-state effects in high-multiplicity pp collisions, in which other measurements show surprising similarities with those in heavy-ion collisions.

The analysis combines results from several partially independent reconstruction techniques available in ALICE. The decay photons were either detected with the electromagnetic calorimeters, or via the central tracking system using ${\mathrm{e}}^{+}{\mathrm{e}}^{-}$ pairs from conversions in the detector material.
The combination of these methods allows for a large $p_{\mathrm{T}}$ coverage, as well as small statistical and systematic uncertainties.

In this poster, the invariant cross sections of the ${\pi }^0$ and $\eta$ meson in pp collisions at $\sqrt{s}$ = 13 TeV, measured with ALICE, for different charged-particle multiplicity classes will be presented. The measurement covers 0.2 $\le$ $p_{\mathrm{T}}<$ 200 GeV/$c$ for the ${\pi }^0$ and 0.4 $\le$ $p_{\mathrm{T}}<$ 50 GeV/$c$ for the $\eta$ meson. Furthermore, the results will be compared to predictions from event generators and pQCD calculations.

Measurements of the production of hadrons containing heavy quarks (charm and beauty) allow a study of cold nuclear matter (CNM) effects such as gluon saturation, shadowing and energy loss in p-Pb collisions. Understanding these effects is important for the proper interpretation of results in Pb-Pb collisions. In addition, the measurements provide the possibility to investigate the hadronisation mechanism.

In this poster, the first measurement of production cross section and nuclear modification factor of the ${\mathrm{D}}^0$ originating from beauty hadron decays, called non-prompt ${\mathrm{D}}^0$, at midrapidity in p-Pb collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}$ = 5.02 TeV with the ALICE detector will be presented. The non-prompt baryon-to-meson yield ratio ${\mathrm{\Lambda }}_{\mathrm{c}}^{+}/{\mathrm{D}}^0$ will be discussed as well.

We present a new high-statistics measurement of inclusive $J/\psi$ production versus event multiplicity in $p$+$p$ collisions at $\sqrt{s}=500$ GeV with the STAR experiment at RHIC. At mid-rapidity, calorimeter-triggered events are selected for candidate $J/\psi$ detection in the dielectron decay channel. Existing measurements at both $\sqrt{s}=200$ GeV from STAR and $\sqrt{s}=7$ TeV from ALICE have shown a faster-than-linear rise as a function of mid-rapidity multiplicity. Potential dependence on collision energy is examined, and measurements are made separately for several intervals over a broad $J/\psi$ transverse momentum range. Proposed explanatory mechanisms, including multi-parton interactions, string screening, and high gluon radiation are discussed, along with the guidance this measurement and related probes provide to model calculations.