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Quark Matter 2023 is the XXXth International Conference on Ultra-relativistic Nucleus-Nucleus Collisions, which will be held in Houston, Texas, USA. This conference brings together theoretical and experimental physicists from around the world to discuss new developments in high-energy heavy-ion physics. The focus of the discussions is on the fundamental understanding of strongly-interacting matter at extreme conditions, as formed in ultra-relativistic nucleus-nucleus collisions, as well as on emergent QCD phenomena in high-multiplicity proton-proton and proton-nucleus collisions.
The scientific program will cover the following topics:
The observation of hyperon polarization has revealed the existence of large vorticities in the medium created by heavy-ion collisions. Global polarization indicates vorticities perpendicular to the reaction plane due to the system's orbital angular momentum. The difference of global polarization between $\Lambda$ and $\bar{\Lambda}$ hyperon can provide essential insights into the late-stage magnetic field sustained by the QGP.
With the high-statistics data collected by the STAR experiment for isobar Ru+Ru and Zr+Zr collisions at $\sqrt{s_{\mathrm{NN}}} = 200$ GeV, we present the measurements of global polarization for $\Lambda$, $\bar{\Lambda}$, and $\Xi^{\pm}$ as a function of centrality, transverse momentum, pseudorapidity, and azimuthal angle relative to the event plane. In addition, we present the correlation between the initial tilt of the system and the vorticity through the dependence of the $\Lambda$ global polarization and directed flow on the first-order flow vector ($q_1$) in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}} = 19.6$ GeV.
The local polarization indicates vorticities along the beam direction due to anisotropic transverse expansion of the medium. We present the first measurements of $\Lambda$, $\bar{\Lambda}$ hyperon local polarization in isobar collisions at $\sqrt{s_{NN}}$= 200 GeV and Au+Au collisions at $\sqrt{s_{NN}}$= 19.6, 27 GeV. Comparisons with previous measurements in Au+Au and Pb+Pb collisions at RHIC and LHC provide important insights into the collision system size and energy dependence of the vorticities. Furthermore, the local polarization measurements at lower beam energies can probe the predicted baryonic spin hall effect in a dense baryonic environment in heavy-ion collisions.
The interplay of the chiral anomaly and the strong magnetic or vortical field created in the off-central heavy-ion collisions can give rise to anomalous chiral effects in the quark--gluon plasma. These include the Chiral Magnetic Effect (CME), the Chiral Magnetic Wave (CMW) and the Chiral Vortical Effect (CVE). The study of these novel phenomena is of fundamental significance since they may reveal the topological structure of vacuum gauge fields, as well as the possible local violation of P and/or CP symmetries in strong interactions.
In this talk, we present comprehensive measurements of anomalous chiral effects in Xe--Xe and Pb--Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.44 TeV and 5.02 TeV, respectively, with ALICE. The CME is studied using the charge-dependent two- and three-particle correlators. The Event Shape Engineering (ESE) technique, together with the Monte Carlo Glauber and T$_{\rm R}$ENTo simulations of the magnetic field are employed to derive an upper limit on the CME signal. The ESE technique is also adopted to quantitatively constrain the strength of the CMW signal, which is examined by the correlation between the charge asymmetry and the elliptic flow. The CVE is studied using several combinations of azimuthal correlations between baryon pairs at different kinematic windows, such as $\Lambda-p$, $\Lambda-\Lambda$ or $p-p$. These measurements provide new insights into the experimental search for anomalous chiral effects in heavy-ion collisions.
Hydrodynamics provides quantitative descriptions of various flow measurements in heavy-ion collisions, suggesting the strongly-coupled nature of the hot QCD matter. A ubiquitous phenomenon in fluid dynamics is the formation of vortex rings. In heavy-ion collisions, different conditions can give rise to toroidal vortex structure in the QGP medium, such as the medium's response to jet thermalization [1] and the early-stage longitudinal dynamics in asymmetric collisions [2]. Considering these scenarios, in this talk, we will present a systematic study of how $\Lambda$ hyperon's polarization can probe these toroidal vortex structures in QGP. We define a "ring observable" in terms of the $\Lambda$ production plane polarization [2]. It represents a measure of the effects caused by the vorticity induced in the ring formation. By conducting event-by-event analysis with the state-of-the-art (3+1)D theoretical framework [3, 4], we demonstrate that this ring observable is a highly sensitive probe for thermalizing energy-momentum currents deposited from high-energy jets and for the early-time longitudinal dynamics in asymmetric collision systems. An experimental indication of such ``smoke rings'' formed in the QGP would represent a significant advancement in studying the emergent phenomena of many-body QCD at multiple length scales.
[1] W. M. Serenone, D. D. Chinellato, M. A. Lisa, C. Shen, J. Takahashi and G. Torrieri, "$\Lambda$ polarization from thermalized jet energy", Phys. Let. B 820, 126500 (2021)
[2] M. A. Lisa, J. G. P. Barbon, D. D. Chinellato, W. M. Serenone, C. Shen, J. Takahashi and G. Torrieri, "Vortex rings from high energy central p+A collisions", Phys. Rev. C 104, no.1, 011901 (2021)
[3] V. H. Ribeiro, W. M. Serenone, D. D. Chinellato, M. A. Lisa, C. Shen, J. Takahashi and G. Torrieri, "$\Lambda$ polarization from vortex ring as medium response for jet thermalization", arXiv:2305.02428 [hep-ph] (2023)
[4] C. Shen and B. Schenke, "Longitudinal dynamics and particle production in relativistic nuclear collisions", Phys. Rev. C 105, no.6, 064905 (2022)
The global spin alignment of particles produced in heavy-ion collisions can reveal valuable information about the strong force field and the properties of the quark-gluon plasma. The STAR collaboration recently observed a large global spin alignment of $\phi$-mesons in Au+Au collisions using the data from the first phase of the RHIC Beam Energy Scan program (BES-I) [1]. This cannot be explained by conventional mechanisms but may be attributable to the influence of vector meson force fields. In this contribution, we present new measurement of $\rho^0$ global spin alignment as a function of transverse momentum ($p_T$) and centrality for Au+Au, Ru+Ru, and Zr+Zr collisions at $\sqrt{s_{NN}}$ = 200 GeV. We discuss the implications of our results for the search for the Chiral Magnetic Effect, as the global spin alignment of $\rho^0$ mesons can effectively influence the measurement of charge separation across the reaction plane. Additionally, we present new precision and differential measurements of $\phi$-meson global spin alignment as a function of $p_T$, centrality, and rapidity (y) at $\sqrt{s_{NN}}$ = 7.7, 14.6, and 19.6 GeV, using higher-statistics data from the BES-II program. Furthermore, we have conducted a comparative study of the global spin alignment of $\phi(s,\bar{s})$, $\omega(u,\bar{u},d,\bar{d})$, and $J/\psi(c,\bar{c})$ through hadronic or leptonic decay modes in isobar collisions of Ru+Ru and Zr+Zr at $\sqrt{s_{NN}}$ = 200 GeV. These studies with more differential measurements and with vector mesons of various quark contents aim to understand the role of the strong field in nuclear structure and the evolution of nuclear matter. The addition of new particle species and measurements through previously unexplored decay channels can help understand the intricate effects of in-medium and hadronization mechanisms on global spin alignment.
Over the past decade, considerable research effort has focused on investigating macroscopic consequences of anomalies in quantum field theories. In particular, chiral matter is expected to exhibit novel transport phenomena arising from the interplay between quantum anomalies and electromagnetic and vortical fields [1]. In order to study these effects in fluid systems like the quark-gluon plasma formed in heavy-ion collisions, it is important to develop consistent theories of relativistic chiral hydrodynamics which capture the underlying anomaly and include dissipation. Attempts to develop such theories--even their dissipationless counterparts--have suffered from fundamental issues of acausality, instability, and ill-posedness of the initial value problem [2]. Following an effective field theory approach [3-7], we have constructed a first-order relativistic chiral hydrodynamic theory which is stable and causal within a range of values of transport coefficients. This is the first viscous theory of relativistic chiral hydrodynamics that can be used in numerical simulations of heavy-ion collisions.
[1] D. E. Kharzeev, J. Liao, S. A. Voloshin, G. Wang, Prog. Part. Nucl. Phys. 88 (2016) 1-28.
[2] E. Speranza, F. S. Bemfica, M. M. Disconzi, J. Noronha, Phys. Rev. D 107 (2023) 5, 054029.
[3] F. S. Bemfica, M. M. Disconzi, J. Noronha, Phys. Rev. D 98 (2018) 10, 104064.
[4] P. Kovtun, JHEP 10 (2019) 034.
[5] F. S. Bemfica, M. M. Disconzi, J. Noronha, Phys. Rev. D 100 (2019) 10, 104020.
[6] R. E. Hoult, P. Kovtun, JHEP 06 (2020) 067.
[7] F. S. Bemfica, M. M. Disconzi, J. Noronha, Phys. Rev. X 12 (2022) 2, 021044.
Effects from quark chirality in heavy-ion collisions probe the topological sector of Quantum Chromodynamics, where parity and charge-parity symmetries are violated locally in strong interactions. However, the experimental observables for the chiral magnetic/vortical effect (CME/CVE) are dominated by elliptic flow and nonflow backgrounds. Recent STAR isobar data revealed a substantial background in the CME observable that prevented an unambiguous observation of the difference between two isobars. The Au+Au system has significant advantages over the isobar collisions, such as the larger magnetic fields and the lower statistical fluctuations.
We improve the analysis method with event shape variables (ESV), and apply it to Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 7.7, 14.6, 19.6, 27, and 200 GeV in the search of the CME and CVE. After categorizing events based on ESV and extrapolating the CME/CVE observable towards zero flow limit, we report the $\Delta \gamma$ measurements using $h$-$h$ and $\Lambda$-$p$ correlations. To fully assess the possible CME signal, we employ a broad spectrum of observables and analysis techniques: with and without the particle pair information in constructing ESVs, utilizing invariant mass for differential studies, exploiting STAR Event Plane Detector and Zero-Degree Calorimeter to minimize nonflow backgrounds. We will discuss the physics implications on the beam energy dependence of the CME/CVE searches.
Directed and elliptic flow ($v_{1}$, $v_{2}$) are sensitive to the dynamics of heavy-ion collisions at the early stage of the system evolution and the equation of state (EoS) of the medium. The $v_1$ slope ($dv_1/dy$) at mid-rapidity of net-baryons is expected to be sensitive to the first-order phase transition. Also, triangular flow ($v_3$) provides valuable information on the initial geometry fluctuations and transport properties of the medium. Studying these flow harmonics for various identified particles at different energies provides insights into the medium going through QCD phase transition. In particular, (multi-) strange hadrons with small hadronic cross-sections are cleaner probes of the early stages of heavy-ion collisions. A comprehensive study of light and (multi-) strange hadrons provides valuable insights into the subsequent stages of the medium evolution.
In this talk, the measurements of $v_1$, $v_2$, and $v_3$ for both light and (multi-) strange hadrons at $\sqrt{s_{NN}}$ = 3.0, 3.2, 3.5, 3.9, 7.7, 9.2, 11.5, 14.6, and 19.6 GeV, utilizing the enhanced capabilities of the STAR detectors and datasets with increased statistics from the second phase of the RHIC beam energy scan (BES-II) program, will be presented. The centrality dependence of anisotropic flow and the test of number of constituent quark (NCQ) scaling will be shown. Also, the energy and centrality dependence of $v_1$ slope and $p_T$-integrated $v_2$ will be discussed. The data will be compared with different model calculations, and the inferences on the QCD phase structure and EoS of nuclear matter in the high baryon density region will be discussed.
Most of our experimentally-driven knowledge about the early stages of a heavy-ion collision comes from analysis of measurements made near mid-rapidity. However, much information about the dynamics is encoded in rapidity-dependent behavior, and there exists a large amount of experimental data available to constrain this rapidity dependence. To leverage this information, we perform a systematic model-to-data comparison using three-dimensional hydrodynamic simulations of multiple collision systems --- large and small, symmetric and asymmetric, at different collision energies, from both RHIC and the LHC. Specifically, we perform fully 3D multi-stage hydrodynamic simulations initialized by a parameterized model for rapidity-dependent energy deposition [1] and we calibrate on a range of observables such as hadron multiplicity, anisotropic flow vectors, and mean transverse momentum --- including their rapidity-dependent fluctuations and correlations. We utilize Bayesian inference to constrain properties of the early- and late-time dynamics of the system, and further harness the results to do experimental design and study the effectiveness of various potential measurements (e.g. from upgraded detectors) at improving these constraints.
[1] C. Shen and B. Schenke, “Longitudinal dynamics and particle production in relativistic nuclear collisions,” Phys. Rev. C 105, no.6, 064905 (2022)
[arXiv:2203.04685].
Using a (3+1)-dimensional hybrid framework with parametric initial conditions, we study the rapidity-dependent directed flow $v_1(y)$ of identified particles, including pions, kaons, protons, and lambdas in heavy-ion collisions. Cases involving Au+Au collisions are considered, performed at $\sqrt{s_{\rm NN}}$ ranging from 7.7 to 200 GeV. The dynamics in the beam direction is constrained using the measured pseudo-rapidity distribution of charged particles and the net proton rapidity distribution. Within this framework, the directed flow of mesons is driven by the sideward pressure gradient from the tilted source, and that of baryons mainly due to the initial asymmetric baryon distribution with respect to the beam axis driven by the transverse expansion. Our approach successfully reproduces the rapidity- and beam energy-dependence of $v_1$ for both mesons and baryons. We find that the $v_1(y)$ of baryons has strong constraining power on the initial baryon stopping, and together with that of mesons, the directed flow probes the equation of state of the dense nuclear matter at finite chemical potentials. We also provide predictions for the upcoming STAR Beam Energy Scan II measurements of the pseudo-rapidity dependent $v_1$ for charged particles at 27 GeV.
[1] L. Du, C. Shen, S. Jeon, and C. Gale, "Probing initial baryon stopping and equation of state with rapidity-dependent directed flow of identified particles", arXiv: 2211.16408.
The $f_0(980)$ is a candidate exotic hadron, first observed by $\pi\pi$ scattering in the 1970’s. Its configuration still remains controversial— it can be a normal $s\bar{s}$ meson, a tetraquark $s\bar{s}q\bar{q}$ state, a $q\bar{q}g$ hybrid, or a $\mathrm{K}\bar{\mathrm{K}}$ molecule. Relativistic heavy ion collisions are in a unique position to identify the $f_0(980)$ quark content by the empirical NCQ (number of constituent quarks) scaling of elliptic flow $v_{2}$. In this talk, we present the first reconstruction of $f_0(980)$ via its main decay channel, $f_0(980) \to\pi^+\pi^-$, using proton-lead collisions recorded by the CMS experiment at 8.16 TeV. The $f_0(980)$ yield is studied as a function of the azimuthal angle relative to the event plane, reconstructed from the forward hadron calorimeters, to extract the $v_{2}$ parameter. The $v_{2}$ of the $f_0(980)$ is then compared to $v_{2}$ values from other hadrons to infer in a novel way the quark content of the $f_0(980)$.
Intermediate pT jets (minijets) are created by initial hard scatterings in heavy-ion collision experiments. They can constitute a significant portion of the particle multiplicity but do not lend themselves to hydrodynamic treatment as their transverse momenta are larger than the typical saturation scale of the bulk matter.Their orientation is independent of the underlying event and they can significantly reduce flow in the collective motion of the bulk medium. They also introduce an additional source of fluctuations.
We study minijets in a new jet+hydro concurrent framework where jet quenching leads to energy and momentum injection in the QGP. Minijets are sampled using PYTHIA and hydro is initialized using the IPGlasma framework. Both of these are concurrently evolved using MUSIC with the minijet quenching being governed by the Hybrid Model. Both the jet and thermal hadrons do hadronic cascade through UrQMD after the freezeout.
We find that this effort requires substantial recalibration of the transport coefficients in hydrodynamic simulations to explain the data. As extraction of transport properties is one of the major goals of the heavy-ion program, we posit that this significant contribution needs to be accounted for. We will also discuss the effect of these minijets on observables like pT-spectra, flow vn and correlations between different vn_s. We also look at the relation between initial state spatial anisotropy and the final state momentum anisotropy in the presence of minijets.
The early dynamics in heavy-ion collisions involves a rapid, far from equilibrium evolution. This early pre-equilibrium stage of the dynamics can be modeled using kinetic equations. The effect of this pre-equilibrium stage on final observables derived from transverse momenta of emitted particles is negligible. Therefore, the kinetic equations in the relaxation time approximation for a non-boost invariant system are solved (P.Bozek Phys.Rev.C 107 (2023) 034916). The asymmetry of the flow with respect to the reaction plane at different rapidities is found to be very sensitive to the degree of non-equilibrium in the evolution. This suggests that the rapidity odd directed flow is a sensitve probe of the occurrence of non-equilibrium effects and could be used to estimate the asymmetry of the pressure between the longitudinal and transverse directions. The study of kinetic evolution in the longitudinal direction allows also a modelling of the early pre-Bjorken flow stage of the equilibration.
Higher-order cumulants ($C_n$) of net-baryon distributions are sensitive to the nature of the QCD phase transition. Recent lattice QCD calculations [1] suggest a negative $C_5/C_1$ and $C_6/C_2$ in the crossover regime at small baryon chemical potential ($\mu_B \leq$ 110 MeV). In addition, lattice QCD predicts a special ordering of cumulant ratios for systems of thermalized QGP [2]: $C_3/C_1 > C_4/C_2 > C_5/C_1 > C_6/C_2$. Both predictions can be tested in heavy-ion collision experiments by measuring higher-order cumulants of the net-proton multiplicity distributions.
In the high $\mu_B$ region of the QCD phase diagram, proton multiplicity distributions are utilized to probe characteristics of the phase transition. The variance of proton multiplicity within azimuthal subvolumes of phase space may provide insight into local parton density fluctuations. The deviation of this variance from a binomial baseline along with proton factorial cumulants over the full azimuth [3] may be observables sensitive to a possible first-order phase transition.
In this talk, we report measurements of net-proton $C_5/C_1$ and $C_6/C_2$ in Au+Au collisions with center-of-mass energies from 3 GeV to 200 GeV, where the 3 GeV data are from the fixed-target program and the other data sets are from the Beam Energy Scan program phase I at RHIC-STAR. Proton factorial cumulants and the variance of proton multiplicities in azimuthal partitions are also presented. The cumulant measurements are compared with a QCD-based FRG model, UrQMD, and HRG calculations as well as lattice QCD calculations. The AMPT and MUSIC+FIST models are used as non-critical references in the search for local density fluctuations.
[1] W.-j. Fu et al. \textit{Physical Review D} 104.9 094047 (2021).
[2] A. Bazavov et al. \textit{Physical Review D} 101.7 074502 (2020).
[3] A. Bzdak and V. Koch. \textit{Physical Review C} 100.5 051902 (2019).
It has long been understood that non-monotonic variation of non-Gaussian cumulants of particle multiplicities as a function of decreasing collision energy and, hence, increasing baryon chemical potential $\mu_B$ can yield tell-tale signatures of the presence of a possible critical point in the QCD phase diagram. In this talk, we shall present quantitative estimates for the magnitude and $\mu_B$-dependence of the skewness and kurtosis of the proton multiplicity as a function of the separation $\Delta T$ between the temperature at a critical point and at freezeout. These provide a modern update of estimates first attempted in [1], for the first time including the effects of the change in the sign of the critical contribution to the kurtosis discovered in [2] in a way that incorporates the mapping between the universal physics around an Ising critical point onto the QCD phase diagram [3,4].
Several of us have recently quantified the reduction in the magnitude of the Gaussian cumulant of the proton multiplicity relative to equilibrium expectations, arising because both critical slowing down and baryon number conservation limit the growth of critical fluctuations [5]. In this talk, we describe how the dynamics in the critical regime (including critical slowing down and baryon number conservation) limit the growth of the non-Gaussian cumulants. It has been understood since they were first proposed as signatures of a critical point that dynamical effects make the actual cumulants much smaller than they would be in equilibrium; for the first time, we estimate how much smaller. We close by using the newly developed maximum entropy freezeout procedure [6] to make estimates of the magnitude of the skewness and kurtosis of proton multiplicity that can be expected in RHIC BES data if nature places a critical point near where these collisions freeze out.
[1] Athanasiou, Rajagopal, Stephanov, arXiv:1006.4636.
[2] Stephanov, arXiv: 1104.1627.
[3] Parotto et al, arXiv:1805.05249.
[4] Karthein et al, arXiv:2103.08146.
[5] Pradeep, Rajagopal, Stephanov and Yin, arXiv:2204.00639.
[6] Pradeep, Stephanov, arXiv:2211.09142.
The recent measurements of femtoscopic correlations at NA61/SHINE, using small systems, unravel that the shape of the particle emitting source is not Gaussian. The measurements are based on alpha-stable symmetric L\'evy sources, and we discuss the average pair transverse mass dependence of the source parameters. One of the parameters, the L\'evy exponent $\alpha$, is of particularly importance. It describes the shape of the source, which, in the vicinity of the critical point of the phase diagram, may be related to the critical exponent $\eta$. Its measurement hence may contribute to the search for and characterization of the critical endpoint of the phase diagram.
Moreover, one of the most important goals of NA61/SHINE is to investigate and understand the phase structures of this matter. The investigation of the phase-diagram can be achieved by varying the beam momentum (13A-150(8)A GeV/c) or by changing the collision system (p+p, p+Pb, Be+Be, Ar+Sc, Xe+La, Pb+Pb). This method enables to perform a two-dimensional scan of the phase diagram of QCD. Investigating HBT correlations are related to the critical exponent $\eta$, describing the spatial correlation. The search in the collisions reveals the properties of sQGP and possible signs of the critical endpoint.
Calculations of baryon number fluctuations up to the sixth order at finite temperature and density in Ref.[1] have been extended to regime of high baryon chemical potentials with 400 MeV $\leq \mu_B\leq 700$ MeV. A peak structure is found for the dependence of the kurtosis of baryon number distributions, i.e., $R^{B}_{42}=\chi^{B}_{4}/\chi^{B}_{2}$, on the collision energy in a range of 3 GeV $\leq\sqrt{s_{\mathrm{NN}}}\leq 7.7$ GeV [2]. The computation is done within the functional renormalization group approach with a critical end point located at around $(T,\,\mu_B)_{\mathrm{CEP}}\sim(100,\,640)$ MeV in the phase diagram, which is in agreement with recent estimates from first-principle QCD calculations. Errors of calculated results arising from, e.g., the chemical freeze-out curves, locations of CEP, effects of baryon number conservation at low collision energy etc., have been evaluated in detail.
Reference:
[1] Wei-jie Fu, Xiaofeng Luo, Jan M. Pawlowski, Fabian Rennecke, Rui Wen, Shi Yin, Phys. Rev. D 104, 094047, 2021, arXiv: 2101.06035 [hep-ph].
[2] Wei-jie Fu, Xiaofeng Luo, Jan M. Pawlowski, Fabian Rennecke, Shi Yin, in preparation.
Predictions for the QCD critical point are made using Bayesian inference techniques within the holographic gauge/gravity correspondence. For that, we employ a Einstein-Maxwell-Dilaton (EMD) model capable of reproducing the latest lattice QCD results at zero and finite baryon density, known to predict a high-density critical endpoint. For the first time, we numerically find the posterior probability distribution for holographic model parameters from the lattice data at zero chemical potential, and extract their most likely values. This is possible thanks to new numerical developments which, by boosting the performance of our calculations, allow us to sample a large number of fits to the data via Monte Carlo methods. Thus, we find the maximum a posteriori estimate for the location of the critical point, as well as estimates for the corresponding statistical error bands. We determine the linear combination of model parameters which is the most relevant for these uncertainties and investigate its role for the equation of state at lower densities. Our analysis is performed for two competing model parametrizations, one of which may or may not present a critical point for samples of the prior distribution. We use the posterior distribution for this parametrization to infer the probability that a QCD critical point exists and is situated in a region of the phase diagram that can be probed by ongoing and future heavy ion collision experiments. Preliminary results favor a critical point around a baryon chemical potential of $570 - 650$ MeV and a temperature of $99 - 107$ MeV, with most of the uncertainty concentrated along a single line.
Subensemble Acceptance Method (SAM) [1,2] is an essential link between measured event-by-event fluctuations and their grand canonical theoretical predictions such as lattice QCD. The method allows quantifying the global conservation law effects in fluctuations. In its basic formulation, SAM requires a sufficiently large system such as created in central nucleus-nucleus collisions and sufficient space-momentum correlations. Directly in the spinodal region of the First Order Phase Transition (FOPT) different approximations should be used that account for finite size effects. Thus, we present the generalization of SAM applicable in both the pure phases, metastable and unstable regions of the phase diagram [3]. Obtained analytic formulas indicate the enhancement of fluctuations due to crossing the spinodal region of FOPT and are tested using molecular dynamics simulations. A rather good agreement is observed. Using transport model calculations with interaction potential we show that the spinodal enhancement of fluctuations survives till the later stages of collision via the memory effect [4]. However, at low collision energies the space-momentum correlation is not strong enough for this signal to be transferred to second and third order cumulants measured in momentum subspace. This result agrees well with recent HADES data on proton number fluctuations at $\sqrt{s_{NN}}=2.4$ GeV which are found to be consistent with the binomial baseline of non-interacting hadrons [5]. It indicates that the large fluctuations observed in HADES data do not signal the presence of phase transition and their origin is yet to be identified. We suggest a crosscheck of this picture based on calculating the correlation between proton multiplicities in two non-overlapping rapidity intervals.
[1] V.Vovchenko, O.Savchuk, R.P., M.I.Gorenstein, V.Koch, Phys.Lett.B 811 (2020) 024908.
[2] R.P. et al., Phys. Rev. C 102 (2020) 024908.
[3] V.Kuznietsov, O.Savchuk, R.P., V.Vovchenko, M.I.Gorenstein, H.Stoecker, 2303.09193 (2023)
[4] O.Savchuk, R.P., A.Motornenko, J.Steinheimer, M.I.Gorenstein, V.Vovchenko, Phys. Rev. C 107 (2023) 2, 024913
[5] O.Savchuk, R.P., M.I.Gorenstein, Phys.Lett.B 835 (2022) 137540
Charmonia have long been recognized as a valuable probe of the nuclear matter in extreme conditions, such as the strongly interacting medium created in heavy-ion collisions and known as quark-gluon plasma (QGP). At LHC energies, the regeneration process due to the abundantly produced charm quarks, was found to considerably affect measured charmonium observables. Comprehensive production measurements of charmonia, including both ground and excited states, are crucial to discriminate among different regeneration scenarios assumed in theoretical calculations. Charmonia can also be sensitive to the initial state of the heavy-ion collision. In particular, their spin-alignment can be affected by the strong magnetic field generated in the early phase, as well as by the large angular momentum of the medium in non-central collisions. The determination of the component originating from beauty hadron decays, known as non-prompt charmonium, grants a direct insight into the nuclear modification factor of beauty hadrons, which is expected to be sensitive to the energy loss experienced by the ancestor beauty quarks inside the QGP. Furthermore, once it is subtracted from the inclusive charmonium production, it allows for a direct comparison with prompt charmonium models.
In this contribution, newly published results of inclusive J/$\psi$ production, including yields, average transverse momentum and nuclear modification factors, obtained at central and forward rapidity in Pb--Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV, will be presented. At midrapidity, newly published measurements of prompt and non-prompt J/$\psi$ production will also be shown. Recently published results obtained at forward rapidity in Pb--Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV will be discussed. These include, among others, the $\psi$(2S)-to-J/$\psi$ (double) ratio and the $\psi$(2S) nuclear modification factor, as well as the J/$\psi$ polarization with respect to a quantization axis orthogonal to the event-plane. Results will be compared to available model calculations.
Heavy quarks are one of the most powerful probes to study the properties of quark-gluon plasma. We present new results on nuclear modification factors of $\mathrm{B}_\mathrm{s}^{0}$ and $\mathrm{B}^{+}$ mesons, using proton-proton (pp) and lead-lead (PbPb) data recorded with the CMS detector in 2017 and 2018, respectively. The measured B meson nuclear modification factors over an extended transverse momentum range provide important information about the diffusion of beauty quarks and the flavor dependence of in-medium energy loss. In addition, understanding the hadronization mechanism is crucial for extracting the transport properties of the QGP. The $\mathrm{B}_\mathrm{s}^{0}/\mathrm{B}^{+}$ yield ratio in pp and PbPb can thus shed light on beauty hadronization mechanisms from small to large systems and on the relevance of parton recombination in the medium. We also report the first observation of the $\mathrm{B}_\mathrm{c}^{+}$ meson in PbPb collisions. Given the low production cross-section in pp collisions, its production could be significantly enhanced by the recombination of beauty with charm quarks present in the hypothesized medium, providing additional insights into the recombination mechanism.
Heavy quarks (charm and beauty) are valuable probes for investigating the properties of the quark-gluon plasma (QGP) formed in ultra-relativistic heavy-ion collisions, as they are mainly produced through hard-scattering processes prior to the formation of the QGP, and their number is conserved during the subsequent QGP evolution. Measurements of the nuclear modification factor $R_{\rm AA}$ of charm and beauty hadrons allow the characterisation of the in-medium energy loss of heavy quarks while traversing the QGP. Information on their diffusion and degree of participation in the medium collective motion can be obtained by measuring the elliptic-flow coefficient $v_2$ of heavy-flavour particles. Complementary insights into heavy-quark fragmentation and energy redistribution can be obtained by measuring angular correlations involving heavy-flavour particles.
In this contribution, the newly published results on the non-prompt $v_2$ coefficient of D$^0$ mesons in Pb--Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV will be shown and compared to measurements of prompt D-meson $v_2$ in the same system. These will be supplemented by recent results of the $v_2$ of heavy-flavour decay muons in p--Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV, providing new insights into possible collective effects in smaller systems. The recent final results of the heavy-flavour decay electron $R_{\rm AA}$ in Pb--Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV will also be reported, together with measurements of prompt and non-prompt D mesons and $\Lambda_{\rm c}^{+}$ baryons. New Pb-Pb results of angular correlations of heavy-flavour decay electrons with charged particles in the same collision system will also be discussed. In view of a better understanding of the in-medium heavy-quark dynamics, the reported ALICE measurements will be compared to predictions from models including different implementations of heavy-quark interaction and hadronisation with the QGP constituents.
The study of charm quark hadrons is an important probe to the processes of hadronization of heavy quarks. More specifically, we present results on the production of $\Lambda_\mathrm{c}$ baryon, the nuclear modification factors ($R_\mathrm{AA}$), and the $\Lambda_\mathrm{c}/\mathrm{D}^{0}$ yield ratios at $\sqrt{s_{_{\mathrm{NN}}}} = 5.02$~TeV in proton-proton (pp) collisions and in different centrality regions in lead-lead (PbPb) collisions, using data recorded with the CMS detector in 2017 and 2018, respectively. The reported $R_\mathrm{AA}$ for $\Lambda_\mathrm{c}$ provides useful information regarding the energy loss mechanism of charm quark in the quark-gluon plasma. Its $p_\mathrm{T}$-dependence is similar to that of other charm and beauty hadrons but with its minimum shifted towards higher $p_\mathrm{T}$. Comparing the $\Lambda_\mathrm{c}/\mathrm{D}^{0}$ production ratio in pp and PbPb collisions suggests that coalescence as an hadronization process is not significant for $p_\mathrm{T} > 10$~GeV/c. The ratio becomes comparable to the measurements in $\mathrm{e^{+}e^{-}}$ collisions for $p_\mathrm{T} > 30$~GeV/c. We also present results of the $\Lambda_\mathrm{c}$ baryon and $\mathrm{D}^{0}$ meson production and their ratios in proton-lead (Pb) collisions at $\sqrt{s_{_{\mathrm{NN}}}} = 8.16$~TeV as a function of $p_\mathrm{T}$ and final-state multiplicity using the data recorded by the CMS experiment in 2016. We do not observe any significant multiplicity dependence for the baryon over meson ratio for charm hadrons. The difference between the results from charm quarks and that from light quarks, based on a previous study, suggests coalescence processes of heavy quarks saturate earlier than those of light quarks.
We compute the heavy quark momentum diffusion coefficient $\kappa$ using QCD effective kinetic theory for a system going through bottom-up isotropization until approximate hydrodynamization. This transport coefficient describes heavy quark momentum diffusion in the quark-gluon plasma and is used in many phenomenological frameworks, e.g. in the open quantum systems approach. Our extracted nonthermal diffusion coefficient matches the thermal one for the same energy density within 30%. At large occupation numbers in the earliest stage, the transverse diffusion coefficient dominates, while the longitudinal diffusion coefficient is larger for the underoccupied system in the later stage of hydrodynamization.
The hadro-chemistry of bottom quarks produced in hadronic collisions encodes valuable information on the mechanism of color-neutralization in these reactions. We first compute the chemistry of bottom-hadrons in high-energy $pp$ collisions employing statistical hadronization with a largely augmented set of states beyond the currently measured spectrum. This enables a comprehensive prediction of fragmentation fractions of weakly decaying bottom hadrons for the first time and a satisfactory explanation of the existing measurements in $pp$ collisions at the LHC. Utilizing the bottom hadro-chemistry thus obtained as the baseline, we then perform transport simulations of bottom quarks in the hot QCD matter created in PbPb collisions at the LHC energy and calculate the pertinent bottom-hadron observables. We highlight the transverse momentum ($p_T$) dependent enhancement of the ratios (relative to their $pp$ counterparts) between different species of bottom hadrons ($\bar{B}_s^0/B^-$, $\Lambda_b^0/B^-$ and $\Xi_b^{0-}/B^-$) as a result of bottom quark diffusion and hadronization in the Quark-Gluon Plasma (QGP).
Reference: Min He and Ralf Rapp, arXiv: 2209.13419
Quark-gluon plasma, which is a strongly coupled liquid at its natural length scales, must at the same time feature weakly coupled quark and gluon quasiparticles that appear only in hard processes that can resolve its short-length structure. In particular, high-energy partons in a jet shower can scatter off, and kick, the quark and gluon quasiparticles within a droplet of QGP when these Moliere scattering processes occur with a large enough momentum transfer. Here, we implement this physics within the hybrid strong/weak coupling model for jets in heavy ion collisions.
Throughout its evolution within the expanding cooling droplet of QGP, the shower of jet and recoil partons inject energy and momentum into the QGP, producing wakes. The large impact of the wakes generated by the hydrodynamic response of the medium on jet observables makes finding distinctive signatures of scattering off QGP quasiparticles challenging.
The hybrid model is particularly valuable for identifying observables that are more/less sensitive to consequences of scattering off quasiparticles and less/more sensitive to consequences of wakes in the QGP because when we turn Moliere scattering off the model contains no effects of scattering — energy loss in the model arises from strongly coupled physics, not from scattering.
We show that jet shapes and fragmentation functions are more sensitive to the contribution of the wake to the reconstructed, and identify various groomed jet observables (eg soft drop splitting angle, leading $k_T$, and girth) that are insensitive to this contribution and that show reasonable sensitivity to scattering off quasiparticles, with those in gamma-jet events of particular interest. We also investigate Z-hadron correlation observables and Z-jet acoplanarity observables constructed with the winner-take-all definition of the jet direction. We construct several promising observables from inclusive subjets within jets, and show that Moliere scattering increases the number of subjets and yields subjets which are more widely distributed and more widely separated. These observables are unaffected by the wake; they are directly sensitive to “sprouting a new subjet”, the intrinsic feature of Moliere scattering which makes its effects different from those of the wake.
Jet energy loss and transverse momentum broadening are controlled by the jet transport coefficient $\hat{q}$ in the QGP medium. Specifically, jet energy loss correlates with jet propagation length, while transverse momentum asymmetry caused by the gradient of $\hat{q}$ depends on the initial transverse coordinates. We study both the longitudinal and transverse jet tomography in dijet events by triggering the leading jet propagating along the direction of the event plane in heavy-ion collisions. Simulations are performed using the linear Boltzmann transport model with event-by-event 3+1D viscous hydrodynamic backgrounds. We find that the initial jet production positions in the transverse plane can be simultaneously located by combining the dijet transverse momentum imbalance $x_{J} = p^\mathrm{subleading}_{T} / p^\mathrm{leading}_{T}$ and jet transverse momentum asymmetry perpendicular to the initial jet directions for different leading jet $p_{T}$ regions. The jet tomography can be used to scan the initial jet production positions and to study jet quenching observables in detail, such as the medium-modified jet shape and jet fragmentation functions.
In this talk we use the recently introduced energy correlator framework for jet substructure in heavy-ion collisions to show how the radiation pattern of heavy quarks is modified by the presence of the QGP. We present an analytical calculation of the medium-modified 2-point energy correlator of a heavy quark jet determining how the dead-cone is populated by medium-induced radiation. We identify two regimes: the near-massless limit where the deadcone is not affected by the QGP, and the large-mass limit where the in-medium radiation begins to fill the deadcone. This study provides the first illustration of the ability of energy correlators to disentangle complicated competing jet dynamics.
The suppression of jets in heavy-ion collisions can provide detailed information about the hot, dense plasma formed in these collisions at the LHC. Jet quenching in heavy-ion collisions is expected to depend on the mass of the fragmenting parton. For light partons, energy loss via gluon bremsstrahlung is expected to dominate, while for heavy-quark-initiated jets, collisional energy loss may play a more important role. This energy loss mechanism can be studied by measuring differences in the suppression of $b$-tagged and inclusive jets in $pp$ and Pb+Pb collisions. Besides the $b$-tagged jet measurements, an alternative method for probing the interactions of heavy quarks with the plasma is the study of the correlations between heavy-quark pairs, which is sensitive to the relative importance of collisional versus radiative scattering processes. In this talk, we report new ATLAS measurements of $b$-tagged and inclusive jet production as well as the measurement of the yield of correlated muon pairs from heavy-flavor decays in Pb+Pb and $pp$ collisions at $\sqrt{s_\textrm{NN}}~=~5.02$~TeV. For $b$-tagged and inclusive jet, the transverse momentum distributions in Pb+Pb and $pp$ collisions, as well as the nuclear modification factors, $R_{AA}$, in Pb+Pb collisions, are presented together with comparisons to theoretical calculations. The measurement of correlated muon pairs from heavy-flavor decays includes per-event yields, scaled by the nuclear thickness function, $T_{AA} $ will be discussed. Detailed studies of how the shape of the correlation in azimuthal-angle separation between the two muons changes from peripheral to central Pb+Pb collisions and comparison to the corresponding measurements in $pp$ collisions are also presented.
Extensive studies of dijet momentum balance, inclusive jet shapes, and photon-tagged jet fragmentation functions have revealed a significant contribution of low transverse momentum ($p_\mathrm{T}$) particles to the energy momentum balance of dijet and photon-jets. Effects such as medium-induced radiation and medium response could contribute to the enhancement of low-$p_\mathrm{T}$ particles. In this presentation, we utilize the Z boson reconstructed within the dimuon channel, which does not interact with the quark-gluon plasma (QGP) throughout the decay chain before interacting with the detector. Moreover, Z bosons are high precision probes, and their reconstruction does not introduce bias into the underlying event distribution near them, unlike the isolation requirement of photons. This feature enables the selection of a single quark-enriched high-$p_\mathrm{T}$ parton and study the modification of the underlying events associated with this probe. We present the first measurement of the Z boson-tagged underlying event spectra over a large acceptance with respect to the Z boson, using lead-lead data recorded by the CMS detector at 5.02 TeV. This new result can provide an unambiguous signal of the medium-recoil effect, and it could be sensitive to the equation of state and the speed of sound of the QGP.
Previous analyses have shown a narrowing effect in the inclusive jet substructure. While this narrowing effect could be a result of jet quenching, it could also be caused due to a selection bias by which very quenched and broader jets are filtered out from the considered jet transverse momentum window. Photon-tagged jets, which correspond to a quark-enriched sample, can significantly reduce this potential selection bias and the effect coming from the change in the quark versus gluon fraction. They also allow for a selection on the degree of quenching. In this presentation, we show new photon-tagged jet results using proton-proton and lead-lead collisions at $\sqrt{s_{_{\mathrm{NN}}}} = 5.02$~TeV recorded with the CMS detector in 2017 and 2018, respectively. We present the decorrelation of jet axes calculated with energy-weighted and winner-take-all recombination schemes and compare the results between photon-tagged jets and inclusive jets. We also explore the modification of the groomed jet radius and angularity in PbPb collisions relative to pp collisions for jets that have lost up to 60\% of their initial energy in the medium. The findings of these studies will contribute to a better understanding of the quark-gluon plasma and its properties.
We simulate the space-time dynamics of high-energy collisions based on a microscopic kinetic description, in order to determine the range of applicability of an effective description in relativistic viscous hydrodynamics [1,2]. We find that hydrodynamics provides a quantitatively accurate description of collective flow when the average inverse Reynolds number $\mathrm{Re}^{−1}$ is sufficiently small and the early pre-equilibrium stage is properly accounted for. By determining the breakdown of hydrodynamics as a function of system size and energy, we find that it is quantitatively accurate in central lead-lead collisions at LHC energies, but should not be used in typical proton-lead or proton-proton collisions, where the development of collective flow can not accurately be described within hydrodynamics.
[1] V.E. Ambruș, S. Schlichting, C. Werthmann. To appear in Phys.Rev.D, arXiv: 2211.14379 [hep-ph]
[2] V.E. Ambruș, S. Schlichting, C. Werthmann. Phys.Rev.Lett. 130 (2023) 152301, arXiv: 2211.14356 [hep-ph]
The formation of light nuclei in heavy-ion collisions can be explained by two models: the thermal model and the coalescence model. The thermal model proposes that light nuclei originate from a thermal source where they are in equilibrium with other particles in the fireball. However, due to their low binding energies, the formed nuclei are unlikely to survive the high-temperature conditions of the fireball. In contrast, the coalescence model suggests that light nuclei are formed later in time by the coalescence of protons and neutrons near the kinetic freeze-out surface. The final-stage coalescence of nucleons would lead to the mass number scaling, where the anisotropic flow of light nuclei scaled by their mass numbers follows closely the anisotropic flow of nucleons. Therefore, comparing the anisotropic flow of light nuclei with protons will help us experimentally test the coalescence model hypothesis. Moreover, compared to elliptic flow ($v_2$), triangular flow ($v_3$) of light nuclei has a better sensitivity to the fluctuating initial conditions as well as the properties of the created systems. This information will provide us with tighter constraints on the theoretical models that describe the production mechanism of light nuclei.
In this talk, we will present the transverse momentum ($p_T$) and centrality dependence of $v_2$ and $v_3$ of $d$, $t$, and $^3$He, as well as their corresponding antinuclei, in Au+Au collisions at energies of $\sqrt{s_{NN}} = 7.7$ -- 54.4 GeV from the Beam Energy Scan phase II (BES-II) program at RHIC-STAR. We will discuss the mass number scaling study of $v_2$ and $v_3$ of light nuclei in the BES-II energies. Additionally, we will compare the experimental results with model calculations that use specific initial conditions and/or nucleon coalescence.
This talk presents a measurement of higher order flow harmonics with order number up to 10 in lead-lead (PbPb) collisions at $\sqrt{s_{_{\mathrm{NN}}}} = 5.02$~TeV, using data collected by the CMS experiment. Higher order flow harmonics probe the initial geometry of heavy ion collisions as well as the viscous damping of flow coefficients during the evolution of the quark-gluon plasma (QGP). By extending the study of flow harmonics to higher orders, we can access information about the QGP's transport properties that is complementary to existing measurements. In this talk, we will present the centrality dependence of flow harmonics up to order 10 and compare them to theory calculations and previous measurements at lower orders. Additionally, we will report the net-charge fluctuations with a pseudorapidity separation up to $\Delta\eta$ = 4.8 in PbPb collisions. All the results presented here provide new precision in probing the sensitivity of initial-state fluctuations and viscosity of the QGP, and deepen our understanding of the collective behavior of the strongly interacting matter.
It is a fundamental question to understand what is the effective carrier of conserved quantum charges inside a proton at high energy. The net baryon and electric charge rapidity distributions in relativistic heavy-ion collisions can elucidate how different
conserved charges are transported along the longitudinal direction during the collision. Recent preliminary measurements in isobar collisions at the Relativistic Heavy Ion Collider (RHIC) show that the scaled net-baryon to net-electric charge number ratio at midrapidity ($B/\Delta Q * \Delta Z/A$) is between 1.2 and 2, in line with predictions from the string junction model. This measurement is compatible with the picture where the baryon number is carried by gluon junctions. In this work, we develop a comprehensive (3+1)D relativistic hydrodynamic framework with multiple conserved charge currents. We employ the 3D MC-Glauber model for the initial conditions, which allows for modeling baryon stopping separately from electric charge stopping within the string junction picture. Simulating the coupled propagation of net baryon and electric charge currents including the charge-dependent lattice-QCD-based equation of state, we study how net baryon and electric charges are evolved during different stages of heavy-ion collisions. We make predictions of net baryon and net electric charge rapidity distributions for Ru+Ru and Zr+Zr collisions at $\sqrt{s_\mathrm{NN}}=200$ GeV, which can be compared with STAR measurements.
We report the first direct evidence of thermalization of the Quark-Gluon Plasma (QGP) formed in ultra-relativistic heavy-ion collision, by studying the fluctuation of mean transverse momentum per particle ($\langle p_t \rangle$) in ultra-central Pb+Pb collision. The recent experimental data from the ATLAS collaboration at the Large Hadron Collider (LHC), provides measurement of variance of $\langle p_t \rangle$ at fixed multiplicity ($N_{ch}$) and a steep fall of the variance is observed over a narrow range of $N_{ch}$, for most of the central collision events (Fig. 14 and 15, \href{https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2021-01/}{ATLAS : HION-2021-01}). Such a behaviour cannot be reproduced by previously existing models, such as HIJING which treats Pb+Pb collisions as a superposition of independent nucleon-nucleon collisions. However, our model results can accurately reproduce the peculiar pattern in the variance of $\langle p_t \rangle$ that is observed by ATLAS. To explain such a novel phenomenon, we argue that at a given multiplicity, the impact parameter ($b$) fluctuation plays an important role; the transverse momentum per particle increases with the increasing impact parameter. A larger $b$ corresponds to a smaller collision volume resulting in a higher density. In relativistic thermodyanimcs, a higher density corresponds to a higher initial temperature which implies a larger energy per particle leading to a larger $\langle p_t \rangle$. Thus at a fixed $N_{ch}$, a higher $\langle p_t \rangle$ at a larger b is the effect of the thermalization of the system at a higher temperature. To illustrate this point further, we provide results for Pb+Pb collision from hydrodynamic simulation with TRENTO + MUSIC at b=0 and compare with corresponding HIJING results. From the hydro results, we find a very strong correlation between $\langle p_t \rangle$ and $N_{ch}$ at fixed impact parameter, which is not observed in HIJING where there is no thermalization. The strong correlation is the consequence of the thermalization that is assumed in the hydro simulation.
( R. Samanta, S. Bhatta, J. Jia, M. Luzum and J-Y Ollitrault, \href{https://arxiv.org/pdf/2303.15323.pdf}{arXiv: 2303.15323} )
This talk presents a measurement of longitudinal decorrelation in $pp$ collisions with ATLAS. The deposited energy in the transverse $(x,y)$ plane is expected to vary, depending on the longitudinal $(z)$ slice examined, which is correlated with the rapidity of the produced particles. Thus, particles from different rapidity slices will have flow vectors that differ in magnitude and orientation due to the longitudinal variation, longitudinal decorrelation, which grows with increasing particle rapidity separation. For flow harmonic $n$, such longitudinal decorrelations have been characterized, for large systems, in terms of $r_n$, the ratio of large-rapidity-gap to small-rapidity-gap correlations. This analysis performs the first measurements of $r_n$ in $pp$ collisions at 5~TeV and 13~TeV. The analysis is carried out via a two-particle correlation method, utilizing charged tracks of varying $\eta$ within $|\eta|<2.5$ and topo-clusters of $4.0<|\eta_\mathrm{ref}|<4.9$. Because non-flow effects are more significant in $pp$ collisions, non-flow template subtraction procedures are applied. Final results are quoted for $r_2$ and its slope $F_2$, over a range of multiplicities. Similar non-flow subtraction techniques are applied to the full multiplicity range of Xe+Xe collision data and the results are compared to the two $pp$ energies at appropriate multiplicities. This gives some of the first detailed information on the correlation between longitudinal and transverse energy deposition in $pp$ collisions.
Deciphering the process of hadronization has long been a formidable challenge, in part due to its non-perturbative nature. Over the years, various phenomenological models have emerged, all attempting to unravel the complexity of hadron production. Despite their different theoretical foundations, many of these models successfully account for the average yield of hadrons. This has spurred the scientific community to search for innovative observables capable of discerning the fundamental principles governing these models. In pursuit of this goal, the ALICE Collaboration has studied an extensive array of event-by-event Pearson correlations between hadrons with distinct quantum numbers. Conducting a system size scan of these measurements unveils a powerful means to identify and analyze emerging QCD phenomena in small collision systems. In this presentation, ALICE will show the latest findings on antiproton--antideuteron and net-kaon--net-Xi correlations in various collision systems (pp, p--Pb, and Pb--Pb). These observables offer the advantage of being unaffected by resonance or weak decays. The measurements will be compared to various hadronization models, delving into the intriguing topic of the onset of thermalization in QCD matter. The measured correlations are used to estimate the correlation volume between hadrons stemming from the conservation of baryon and strange quantum numbers.
The PHENIX experiment at RHIC has a unique large rapidity coverage (1.2$<|\eta|<$2.2) for heavy flavor studies in heavy ion collisions. This kinematic region has a smaller particle density and may undergo different nuclear effects before and after the hard process when compared to mid-rapidity production. The latest PHENIX runs contains a large data set which allows, for the first time, the study of heavy flavor and J/$\psi$ flow at the large rapidity region in Au+Au collisions at $\sqrt{s_{NN}}=$200 GeV. This measurement has the potential to reveal a medium evolution distinct from the one known at the mid-rapidity. This presentation will also report on the analysis status of non-prompt J/$\psi$ coming from B-meson decays at mid-rapidity in $pp$ collisions. This data can reach very low $p_{\rm T}$ B-mesons yields which is typically challenging to be described by pQCD calculations.
Heavy flavor quarks (charm and bottom), produced in the early stages of heavy-ion collisions, serve as excellent probes to study the properties of the Quark-Gluon Plasma (QGP). When traversing the medium, charm quarks suffer from `jet quenching' thanks to the interactions with the QGP. It can manifest as degradation of charm quark energy and modifications to the fragmentation pattern, both of which are predicted to depend on parton flavor and quark mass. The energy loss can be quantified by comparing yields of charmed mesons or tagged charm jets in heavy-ion collisions to those in $p$+$p$ collisions. On the other hand, medium-induced modifications to the jet shower can be studied using the jet fragmentation function, i.e., the transverse momentum ($p_{\rm T}$) fraction of the jet carried by hadrons along the jet axis ($z = \vec{p}_{\rm T, hadron}\textbf{.}\hat{p}_{\rm T, jet}/|\vec{p}_{\rm T, jet}|$).
In this contribution, we report the first measurement of the $\rm D^{0}$ meson production yield at mid-rapidity ($|y| < 1$) in isobar collisions (Ru+Ru and Zr+Zr) at $\sqrt{s_{\text{NN}}} = 200 \text{ GeV}$, with the STAR experiment at RHIC. We present nuclear modification factors as a function of $p_{\rm T}$ for different centrality classes, and compare them to similar measurements in Au+Au collisions at $\sqrt{s_{\text{NN}}} = 200 \text{ GeV}$. We complement the $\rm D^{0}$ meson studies with measurements of $\rm D^{0}$ meson tagged jets in Au+Au collisions at $\sqrt{s_{\text{NN}}} = 200 \text{ GeV}$. For the first time, we show measurements of charm jet fragmentation function in heavy-ion collisions at RHIC, and the nuclear modification factor as a function of $z$. Additionally, we report the yield modifications of $\rm D^{0}$-tagged jets as a function of $p_{\rm T}$ and the radial profile of the $\rm D^{0}$ mesons in these tagged jets. These reported measurements can help constrain theoretical calculations of parton flavor, parton mass and system size dependencies of parton interactions with the QGP.
Quarkonia and open heavy-flavor hadrons are important probes to study the properties of the quark-gluon plasma (QGP) created in heavy-ion collisions. Heavy quarks (charm and bottom) are primarily generated at initial hard platonic scatterings and undergo the whole QGP evolution. Therefore, they are excellent probes of the QGP properties.Production of quarkonia depends on the dissociation and regeneration processes in the QGP, and also on the cold nuclear matter effect. To disentangle these effects and infer QGP properties, it is important to carry out differential precision measurements for various quarkonium states at different collision energies and system sizes. The STAR experiment offers opportunity to study the energy and colliding system size dependence of heavy-flavor production through large statistics samples of isobaric collisions ($^{96}_{44}{\rm Ru}+^{96}_{44} \rm Ru$ and $^{96}_{40}{\rm Zr}+^{96}_{40}{\rm Zr}$) at $\sqrt{s_\mathrm{NN}}$ = 200 GeV, as well as Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 14.6, 19.6, 27 GeV and 54 GeV collected in the phase II of Beam Energy Scan program.
In this talk, the first measurements of $\psi(2\rm{S})$ and $J/\psi$ polarization in heavy-ion collisions at RHIC, performed in isobaric collisions, will be presented. Centrality and transverse momentum dependence of the ratio of $\psi(2\rm{S})$ yield over that of $J/\psi$ will be shown. These results together with measurements of the $J/\psi$ and $\Upsilon$ states yield suppression allow a comprehensive study of binding energy dependent modifications to the quarkonium production in the medium. $J/\psi$ polarization measurement provides a new angle for studying QGP properties and the $J/\psi$ production mechanism. New measurments of inclusive $J\psi$ production in Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 14.6, 19.6 and 27 GeV will be also presented. Furthermore, measurements of central-to-peripheral nuclear modification factors (R$_{\rm CP}$) and elliptic flow ($v_2$) of HFE in Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 54.4GeV will be shown.
Measurements in pp and p--Pb collisions, so-called small systems, besides serving as baseline for studying vacuum production and cold-nuclear matter effects, respectively, have recently shown intriguing features. In particular, measurements in high-multiplicity events have revealed striking similarities with heavy-ion collisions, where the formation of a quark-gluon plasma is expected. One of the possible scenarios proposed for describing these findings, which include among others collective effects, is the presence of multiple parton-parton interactions (MPIs). At LHC energies, MPIs affect both the soft component of the event, as well as the hard scales responsible for heavy-quark production. Quarkonium associated production, such as double J/$\psi$ production in the same event, provides a direct way to study MPIs. Conversely, quarkonium measurements which correlate soft and hard components of the event, such as multiplicity dependent production or azimuthal correlations between quarkonia and hadrons produced in the same event, represent an indirect method to investigate MPIs. In addition, these studies can reveal any other potential underlying mechanisms taking place in the final state, such as possible dissociation effects for loosely bound excited quarkonia. In case of charmonia, the corresponding measurements for the non-prompt component, originating from beauty hadron decays, allows for extending such correlations studies to the open beauty hadron sector.
In this talk, new published measurements of double J/$\psi$ production at forward rapidity, as well as new preliminary multiplicity dependent measurements of non-prompt J/$\psi$ fractions at midrapidity, in pp collisions at $\sqrt{s}$ = 13 TeV, will be shown. Recent multiplicity dependent measurements of $\psi$(2S) and $\Upsilon$($n$S) states ($n$ = 1,2,3), along with excited-to-ground state ratios, carried out at forward rapidity in pp and p--Pb collisions at $\sqrt{s}$ = 13 TeV and $\sqrt{s_{\rm NN}}$ = 8.16 TeV, will be presented. Furthermore, recently published prompt and non-prompt J/$\psi$ production at midrapidity in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 8.16, will be discussed. The status of ongoing analyses on J/$\psi$ production as a function of multiplicity or spherocity at central and forward rapidity, in pp and p--Pb collisions, will also be shown. Results will be compared to available model calculations.
The differences in hadron chemistry observed at e+e- machines versus hadron
colliders may indicate that the mechanisms by which partons evolve into visi-
ble matter are not universal. In particular, the presence of many other quarks
produced in the underlying event may affect the hadronization process. With
full particle ID, precision vertexing, and a high rate DAQ, the LHCb detector
is uniquely well suited to study the hadronization of heavy quarks. This con-
tribution will present LHCb data on hadronization of heavy charm and bottom
quarks, including the first results on the b baryon-to-meson production ratio
versus charged particle multiplicity.
Modifications of quarkonia production in hadronic collisions provide an im-
portant experimental observable that sheds light on the heavy quark interaction
with the nuclear medium. In small collision systems, quarkonia can suffer from
a combination of initial and final state effects such as shadowing and comover
breakup, and possible effects from a deconfined medium. The excited ψ(2S)
state, with a relatively low binding energy, is especially sensitive to these ef-
fects. In this contribution, we will present new LHCb results on J/ψ and ψ(2S)
production in high-multiplicity pp and in pPb collisions, along with comparisons
to the latest theoretical models.
Major high-energy nuclear and particle experiments are challenged by the processing of large volumes of high precision data generated by sophisticated detectors in high-rate collisions, e.g., experiments at RHIC and LHC. To address this challenge, state-of-the-art real-time AI technology is being developed using modern deep neural networks and AI-centric hardware innovations. Supported by the DOE Office of Science Nuclear Physics AI-Machine Learning initiative program, this project aims to process extremely high-rate data streams from the tracking detectors of the upcoming sPHENIX experiment at RHIC by integrating real-time readouts and the intelligent control system that accelerates AI inference with FPGA hardware. This design allows us to collect rare heavy-flavor events with high efficiency in the high rate p+p collisions of O(10) MHz with much limited DAQ bandwidth at 15kHz. The developed approach includes high efficiency heavy-flavor trigger algorithms in the Graph Neural Network framework trained by full sPHENIX p+p collision simulation data, the optimized conversion of AI models into Firmware using the hls4ml package developed by the HEP community, and the deployment of real-time AI technologies on the powerful FELIX-711(712) boards with the Xilinx Kintex Ultrascale FPGA. The successful deployment of AI-based real-time data streaming and reduction at sPHENIX will have significant and immediate impacts: minimizing the computation resources and accelerating the end-to-end pipeline from experiments to physics discovery. Our project delivers a demonstrator that brings essential benefits to a key science driver of the sPHENIX experiment and enables comprehensive studies of heavy-flavor production in p+p and p+Au collisions. Furthermore, this technique and experience can be applied in other fields where high throughput data streams and real-time detector control are required, including the future EIC experiments. This talk presents the progress of the design and implementation of the AI-intelligent heavy-flavor triggering system for sPHENIX, showcasing the potential of AI and FPGA technologies in revolutionizing real-time data processing pipelines for high-energy nuclear and particle experiments.
While experimental studies on jet quenching have achieved a large sophistication, the theoretical description of this phenomenon still misses some important points. One of them is the interplay of vacuum-like emissions, usually formulated in momentum space, with the medium induced ones that demand an interface with a space-time picture of the medium and thus must be formulated in position space. A unified description of both vacuum and medium-induced emissions is therefore lacking.
In this work, we build a toy Monte-Carlo parton shower ordered in formation time, virtual mass, and opening angle, representing equivalent formulations at leading logarithmic accuracy. Aiming at a link with jet substructure, we compute the Lund Plane distributions and trajectories for each ordering prescription. We also compute the distributions in number of splittings and final partons, with the goal of clarifying the differences in shower evolution to be expected from the different ordering variables. Further, we investigate the sensitivity of ordering prescriptions to medium effects by counting the number of events obeying a decoherence condition.
The study of jet substructure in heavy-ion collisions provides multiple tools for incisive exploration of jet-medium interactions and the mechanisms underlying jet quenching. Some results, however, remain disjoint: the jet mass and jet angularities, including girth and thrust, are strongly-correlated observables that have given seemingly conflicted answers on the angular quenching of jets traversing the QGP. ALICE has carried out new systematic measurements of these and other perturbatively-calculable angularities using consistent definitions for the first time, resolving the long-standing girth-mass problem, and revealing quenching effects at broad angles. Concurrently, applying soft drop grooming isolates the narrowing in the core of quenched jets. Grooming can also be employed to resolve medium scattering centers, with varying methods to focus on regions of the splitting phase space.
We present the first application of dynamical grooming in heavy-ion collisions to search for excess $k_{\mathrm{T,g}}$ emissions as a signature of point-like scatters, providing new constraints on searches for in-medium Molière scattering. We also present a new approach for studying jet-medium opacity, based on a time-like rather than angular perspective. By employing a new time reclustering strategy, we potentially enable a time-dependent study of jet substructure observables. We compare all results to assorted jet quenching models, providing new critical information on medium evolution as a function of angular, momentum, and time structure.
This talk presents new measurements of inclusive jet yield suppression and correlation with event-plane orientation to elucidate the kinematic and path-length dependence of jet energy loss due to quenching. We report measurements of the inclusive charged-particle jet yield in central Pb--Pb collisions, with the large uncorrelated background mitigated using a novel event mixing technique. This approach extends the jet $R_{\rm AA}$ to lower jet $p_{\mathrm T}$ than previously achievable, providing significant kinematic overlap with RHIC jet measurements.
In addition to explorations of the low-$p_{\rm T}$ frontier, we report the inclusive charged-particle jet $v_2$ in semi-central Pb--Pb collisions, thereby quantifying the yield dependence relative to the event-plane orientation and probing the pathlength dependence of jet energy loss. We also report more differential measurements of this azimuthal dependence by using event-shape engineering to select specific event topologies, and the jet substructure observable $R_{\rm g}$ to select specific jet topologies. Such measurements improve our understanding of how jet suppression depends on both medium and jet properties.
These results are compared to theoretical calculations, thus providing new insights into jet-quenching phenomenology and its underlying mechanisms.
sPHENIX is a new collider detector at RHIC designed for pioneering studies of the Quark-Gluon Plasma with high-p$_T$ jet and heavy flavor probes. The jet physics program particularly relies on the sPHENIX calorimeter system, which consists of large-acceptance, hermetic electromagnetic and hadronic sections designed for high-resolution measurements of photons, electrons, hadrons, and jets. sPHENIX will begin commissioning with Au+Au collisions at 200 GeV in Spring 2023, with a large expected luminosity for measurements of jet production, structure, and correlations from the first year of data-taking. This talk will first give a technical report of the sPHENIX sub-systems relevant for jet physics and then present the status of the first physics measurements.
Prompt photons are created in the early stages of heavy ion collisions and traverse the QGP medium without any interaction. Therefore, photon-triggered jets can be used to study the jet quenching in the QGP medium. In this work, photon-triggered jets are studied through different jet and jet substructure observables for different collision systems and energies using the JETSCAPE framework. Since the multistage evolution used in the JETSCAPE framework is adequate to describe a wide range of experimental observables simultaneously using the same parameter tune, we use the same parameters tuned for jet and leading hadron studies. The same isolation criteria used in the experimental analysis are used to identify prompt photons for better comparison. For the first time, high-accuracy JETSCAPE results are compared with multi-energy LHC and RHIC measurements to better understand the deviations observed in prior studies. These JETSCAPE results are used to predict upcoming sPHENIX results. This study highlights the importance of multistage evolution for the simultaneous description of experimental observables through different collision systems and energies using a single parameter tune.
We study the time evolution of the density matrix of a high energy quark in the presence of a dense QCD background that is modeled as a stochastic Gaussian color field. At late times, we find that only the color singlet component of the quark’s reduced density matrix survives the in-medium evolution and that the density matrix becomes asymptotically diagonal in both transverse position and momentum spaces. In addition, we observe an accelerated entropy growth due to the larger phase space being explored by the quark and that the quantum and classical quark entropies converge at late times. We further observe that the quark state loses all memory of the initial condition. Combined with the fact that the reduced density matrix satisfies Boltzmann-diffusion transport, we conclude that the quark reduced density matrix can be interpreted as a classical phase space distribution. Finally, we comment on how this approach can offer a generic way to study parton evolution in the QGP and establish a strong connection to initial stage physics.
PHENIX observed a 20\% suppression in the production of high $p_T$ neutral pions
in the most central (0-5\%) $d+$Au collisions at 200 GeV. Through the simultaneous measurement of high $p_T$ direct photons ($\gamma^{dir}$) and $\pi^0$ production for event samples selected by event activity, the final state effects could be disentangled from cold-nuclear-matter effects and event-selection biases that are inherent in using the standard Glauber model. This isolation of final state effects is achieved by approximating the nuclear modification factor by the double ratio $R_{xA}=(\gamma^{dir}/\pi^{0})_{pp}/(\gamma^{dir}/\pi^{0})_{xA}$. While the cold-nuclear-matter effects in $x+$A collisions cancel in the ($\gamma^{dir}/\pi^{0})_{xA}$ ratio, the effective number of binary collisions is given by $N_{\mathrm{coll}}^{\mathrm{exp}} = \gamma^{dir}_{xAu}/\gamma^{dir}_{pp}$, which eliminates the dependence on the Glauber model. In addition, many systematic uncertainties cancel in the double ratio. To shed light on the origin of the observed final state suppression and to test if it is consistent with energy loss in droplets of QGP, the results from $d+$Au collisions are compared to preliminary data from smaller ($p+$Au) and larger ($^3$He$+$Au) collision systems.
One main motivation of the Beam Energy Scan (BES) program at RHIC is to search for the QCD critical point and the onset of deconfinement. Strangeness production has been suggested as a sensitive probe to the early dynamics of the deconfined matter created in heavy-ion collisions. Ratios of particle yields involving strange particles are often utilized to study various properties of the nuclear matter, such as the strangeness and baryon chemical potentials at the chemical freeze-out temperature ($\mu_S/T_{\mathrm{ch}}$ and $\mu_B/T_{\mathrm{ch}}$).
Measurements from the first phase of the BES program have indicated potential changes in the medium properties with decreasing collision energy. However, the precision of those measurements is not sufficient to draw definitive conclusions. During BES phase-II (BES-II), STAR has accumulated high statistics data in Au+Au collisions at various energies, which can help reduce the uncertainties in the strange hadron measurements, in particular for the multi-strange hadrons. Benefiting from the iTPC upgrade, the strangeness measurements are now extended from mid-rapidity (|y|<0.5) to a larger rapidity range (|y|<1.0) as well. In this talk, we will present new STAR measurements of strange hadron ($K_s^0$, $\Lambda$, $\bar{\Lambda}$, $\Xi$, $\bar{\Xi}$, $\Omega$, $\bar{\Omega}$) production in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 14.6, 19.6 GeV from BES-II and $\Omega$($\bar{\Omega}$) production in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV, including transverse-momentum and rapidity spectra, nuclear modification factors, baryon-to-meson and antibaryon-to-baryon ratios. New insights on the collision dynamics will be discussed.
The pseudorapidity distributions and anisotropic flow coefficients of charged particles produced in heavy ion collisions are key observables that characterize the initial conditions and subsequent hydrodynamic evolution of the quark-gluon plasma. Recent LHC Run 3 lead-lead (PbPb) data collected at a center-of-mass per nucleon pair of $\sqrt{s_{_{\mathrm{NN}}}} = 5.36$~TeV allow the study of these effects at a record collision energy. We present the first measurements of the midrapidity charged particle $\mathrm{d}N/\mathrm{d}\eta$ as a function of collision centrality, as well as the Fourier harmonics, $v_{2}$ and $v_{3}$, with two- and four-particle correlations in PbPb collisions recorded at $\sqrt{s_{_{\mathrm{NN}}}} = 5.36$~TeV with the CMS experiment. Taken together, these measurements constrain models of the collision-energy and centrality-dependence of charged particle production, and also shed light on the initial collision geometry and importance of event-by-event fluctuations. These data are compared to similar measurements at different energies, including PbPb collisions at $\sqrt{s_{_{\mathrm{NN}}}} = 5.02$ and xenon-xenon collisions at $\sqrt{s_{_{\mathrm{NN}}}} = 5.44$~TeV.
The investigation of the quark content of hadrons has been a major goal of non-perturbative strong interaction physics. In the last decade, several resonances in the mass range 1000-2000 MeV/$c^2$ have emerged that cannot be explained by the quark model. The internal structure of exotic resonances such as $\rm f_0$, $\rm f_1$, and $\rm f_2$ is currently unknown. Different scenarios are possible ranging from two-quark, four-quark, molecule, a hybrid state, or glueballs. A modification of the measured yields of these exotic hadrons in A--A and p--A collisions as compared to pp collisions has been proposed as a tool to investigate their internal structure.
The excellent particle identification capabilities of the ALICE detector along with the large data sample collected in pp and p--Pb collisions provide an opportunity for multi-differential studies of such high-mass resonances. In this presentation, the first-ever measurement of $\rm f_1$ production in pp collisions and measurements of $\rm f_0$ and $\rm f_2$ production both in pp and p--Pb collisions will be presented. The measurements of their mass, width, and yields will be presented and their sensitivity to the internal structure of these exotic resonances will be discussed. These results will pave the way for future experimental investigations on the internal structure of other exotic hadrons.
Measurements of the dynamical correlations between neutral and charged kaons in central Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV by the ALICE Collaboration display anomalous behavior relative to conventional heavy-ion collision simulators. We consider other conventional statistical models, none of which can reproduce the magnitude and centrality dependence of the correlations. The data can be reproduced by coherent emission from domains which grow in number and volume with increasing centrality. We study the dynamical evolution of the strange quark condensate and show that the energy released during the expansion and cooling of the system may be sufficient to explain the anomaly.
Hadronic resonances have typical lifetimes that are comparable to that of the hadron gas phase created in the late stages of high-energy nuclear collisions. Therefore, a significant fraction of resonances decays inside a high-density medium and their decay daughters may rescatter with other hadrons destroying their initial kinematic correlations. A competing effect is resonance regeneration via pseudo-elastic interactions of hadrons. The interplay between these effects, which may modify the measured yields and transverse-momentum spectra of hadronic resonances, can be studied by measuring the yield ratio of resonances to the corresponding long-lived particle as a function of the hadronic lifetime, i.e. charged-particle multiplicity. In addition, measurements of the differential yields of resonances with different masses, quark content, and quantum numbers help in understanding particle production mechanisms, strangeness production, and parton energy loss.
In this presentation, recent measurements of hadronic resonances in Pb--Pb and Xe--Xe collisions as a function of multiplicity will be presented. Collisions between Xe nuclei provide the ultimate test for validating the picture of the smooth evolution of hadronic rescattering across different collision systems by filling the gap between p--Pb and Pb--Pb multiplicities. Furthermore, the measured resonance yields in Xe--Xe and Pb--Pb collisions are used as an experimental input in a partial chemical equilibrium-based thermal model to constrain the kinetic freeze-out temperature. This is a novel procedure that is independent of assumptions on the flow velocity profile and the freeze-out hypersurface.
Measurements of light flavour particle production in small collision systems at the LHC energies have shown the onset of features (e.g. radial flow) that resemble what is typically observed in nucleus-nucleus collisions and attributed to the formation of a strongly interacting medium.
By performing more differential studies and analysing smaller fractions of the visible cross section the processes behind these unexpected phenomena can be more effectively studied and potentially understood.
In this talk, new results on light flavour particle production measured in high-multiplicity triggered events will be shown and compared with the particle production measured as a function of the underlying event activity.
In addition, thanks to its detector upgrade during LS2, from the beginning of the LHC Run 3 campaign ALICE has collected unprecedented high statistics of pp collisions from the lowest collision energy of $\sqrt{s}$ = 900 GeV to the highest collision energy ever achieved in the laboratory of $\sqrt{s}$ = 13.6 TeV. This mole of data, newly presented in this contribution, is used to complete the scan in multiplicity and collision energy of the light flavour particle production studies extending these measurements to the lowest collision energy available at the LHC.
Particle correlations are a powerful tool to study the properties of the bulk nu-
clear matter produced in relativistic heavy ion collisions. The momentum cor-
relations 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 angu-
lar correlations measure the spatial anisotropy of produced particles, providing
information on collective phenomena arising in the dense nuclear medium. This
contribution will discuss new LHCb measurements of Bose-Einstein correlations
and, for the first time, the collective flow coefficients in the far forward rapidity
region
We report on progress in understanding thermalization in QCD at the full quantum level. Previous studies of thermalization of highly excited states in QCD, as they arise in heavy ion collisions, have either involved the (semi-)classical evolution of highly occupied gluon states or kinetic theory. Both approaches omit or approximate essential properties of quantum mechanical systems including coherence and entanglement. An alternative paradigm of understanding thermalization of an isolated quantum system is the eigenstate thermalization hypothesis (ETH), which states that matrix elements of local observables in the energy eigenstate basis are equal to the corresponding microcanonical ensemble values, up to random corrections that decrease exponentially with the system size. In this talk, we will show results of testing this hypothesis for the 2+1 dimensional SU(2) non-Abelian gauge theory on a lattice. The results indicate a subset of physical states in QCD also satisfy the ETH. We will then discuss physical implications of these results. Finally, the simplifications of the Hamiltonian formulation used in this work will be useful for future quantum simulations of non-Abelian lattice gauge theories.
We discuss the evolution of initial momentum anisotropy in the early-stage quark-gluon plasma. We use kinetic theory to study the far-from-equilibrium evolution of an expanding plasma with an anisotropic momentum-space distribution. We identify slow and fast degrees of freedom in the far-from-equilibrium plasma from the evolution of moments of this distribution. At late times, the slow modes correspond to hydrodynamic degrees of freedom and are naturally gapped from the fast modes by the inverse of the relaxation time. At early times, however, there are an infinite number of slow modes. From the evolution of the slow modes we generalize the paradigm of the far-from-equilibrium attractor to vector and tensor components of the energy-momentum tensor, and even to higher moments of the distribution function that are not part of the hydrodynamic evolution. We predict that initial-state momentum anisotropy decays slowly in the far-from-equilibrium phase and may persist until the relaxation time.
Viscous hydrodynamics serves as a successful mesoscopic description of the QGP produced in relativistic heavy-ion collisions. In order to investigate, how such an effective description emerges from the underlying microscopic dynamics we calculate the non-hydrodynamic and hydrodynamic modes of linear response in the sound channel from a first-principle calculation in kinetic theory. We do this with a new approach wherein we linearize and discretize the collision kernel to calculate eigenvalues directly. This allows us to study the Green's functions at any point in time or frequency space. Our study focuses on scalar theory with quartic interaction and we find that the analytic structure of Green's functions in the complex plane is far more complicated than just poles or cuts which is the first step towards an equivalent study in QCD kinetic theory.
The success of thermal models in extracting freeze-out parameters from particle yields near midrapidity is well known. However, it is essential to investigate their performance with rapidity-dependent measurements at low collision energies, where boost-invariance is expected to be strongly violated. In this study, we calibrate a (3+1)-dimensional multistage hydrodynamic framework using rapidity distributions of charged particles and net protons for Au+Au collisions at $\sqrt{s_{NN}}=7.7–200$ GeV. We observe significant rapidity dependences in thermodynamic properties at the hadronization process near the chemical freeze-out. The effects on the rapidity dependence of particle production due to longitudinal flow and system size are also highlighted. A rapidity-dependent thermal model is developed, incorporating the dynamical features of the multistage framework. We evaluate the performance of different thermal model scenarios in extracting the freeze-out profiles, using the rapidity-dependent yields of the multistage framework and comparing them to the hydrodynamic freeze-out hypersurface as a closure test [1]. Bayesian analysis is applied to constrain the longitudinal flow, system size in rapidity space, and thermodynamic properties for nuclear matter created at low beam energies. Our Bayesian model selection analysis reveals a longitudinal flow stronger than Bjorken in the experimental measurements as beam energy decreases. Our study provides a simple numerical approach for extracting rapidity-dependent thermodynamic parameters at freeze-out for low-beam energy collisions. Furthermore, analyzing freeze-out profiles through data-driven methods using this model offers quantitative guidance to computationally-demanding hybrid approaches [2].
[1] Lipei Du, Han Gao, Sangyong Jeon, and Charles Gale, “Rapidity scan with multistage hydrodynamic and statistical thermal models,” arXiv: 2302.13852.
[2] Han Gao, Lipei Du, Sangyong Jeon, and Charles Gale, “Constraining longitudinal dynamics and freeze-out thermodynamics with Bayesian Analysis in a hydrodynamics-inspired thermal model,” in preparation.
Wouldn't it be nice to solve large N QCD analytically? While QCD is hard, it is fairly easy to solve scalar field theories with many components, such as the O(N) model in the large N limit. Traditional wisdom has it that such theories are ill defined because they have the wrong beta function, possess a Landau pole, and are quantum trivial for N=1. In this talk, I throw out conventional wisdom, and critically re-examine scalar field theories in 4d, borrowing heavily from PT-symmetric field theory results. It's a solvable wonderland with asymptotic freedom, bound states in the infrared and a phase transition in between.
We consider non-equilibrium evolution of non-Gaussian fluctuations crucial for the QCD critical point search in heavy-ion collision experiments. We rely on the hierarchy of relaxation time scales, which emerges in the hydrodynamic regime near the critical point. We focus on the slowest modes which are responsible for observable signatures of the critical point. We derive evolution equations for the non-Gaussian correlators of these modes applicable for an arbitrary relativistic hydrodynamic flow.
[1] X. An, G. Basar, M. Stephanov and H.-U. Yee, arxiv/2212.14029
[2] X. An, G. Basar, M. Stephanov and H.-U. Yee, work in progress
The proper treatment of hadronic resonances plays an important role for many aspects of heavy ion collisions. We expect this to be the case also for hadronization, due to the large degeneracies of excited states, and the abundant production of hadrons from their decays. We show how a comprehensive treatment of excited meson states can be incorporated into quark recombination, and in extension, into Hybrid Hadronization. We discuss in detail the quantum mechanics of forming excited states, utilizing the Wigner distribution functions of angular momentum eigenstates of isotropic 3-D harmonic oscillators. We describe how resonance decays can be handled, based on a set of minimal assumptions, by creating an extension of hadron decays in PYTHIA 8. Finally, we present a study of hadron production by jets using PYTHIA and Hybrid Hadronization with excited mesons up to orbital angular momentum L=4. We find that states up to L=2 are produced profusely by quark recombination.
Photonuclear reactions are induced by the strong electromagnetic field generated by ultrarelativistic heavy-ion collisions. These processes have been extensively studied in ultraperipheral collisions, in which the impact parameter is larger than twice the nuclear radius. In recent years, the observation of coherent J/$\psi$ photoproduction has been claimed in nucleus--nucleus (A--A) collisions with nuclear overlap, based on the measurement of an excess (with respect to hadroproduction expectations) in the very low transverse momentum ($p_{\rm{T}}$) J/$\psi$ yield. Such quarkonium measurements can help constraining the nuclear gluon distribution at low Bjorken-x and high energy. In addition, they can shed light on the theory behind photon induced reactions in A--A collisions with nuclear overlap, including possible interactions of the measured probes with the formed and fast expanding quark-gluon plasma. In order to confirm the photoproduction origin of the very low-$p_{\rm{T}}$ J/$\psi$ yield excess, polarization measurement is a golden observable. It is indeed expected that the produced quarkonium would keep the polarization of the incoming photon due to s-channel helicity conservation. ALICE can measure inclusive and exclusive quarkonium production down to zero transverse momentum, at forward rapidity (2.5 <$\it{y}$< 4) and midrapidity (|$\it{y}$|< 0.9). In this contribution, we will report on the new preliminary measurement of the $\it{y}$-differential cross section and the new first polarization analysis at LHC of coherently photoproduced J/$\psi$ in peripheral Pb--Pb collisions. Both measurements are conducted at forward rapidity in the dimuon decay channel. These results will be discussed together with the recent results on coherent J/$\psi$ photoproduction as a function of centrality at both mid and forward rapidities. Comparison with models will be shown when available.
Dileptons are an invaluable tool for mapping out the phase diagram of QCD because they grant observational access to the entire space-time history of heavy-ion collisions. We calculate thermal dilepton yields from Au+Au collisions at BES energies -- $\sqrt{s_{NN}}$=7.7, 19.6, 27, 54.4, 62.4, 130, and 200 GeV -- using a realistic (3+1)-dimensional multistage dynamical framework. The underlying emission rates, which include baryon chemical potential dependence for the first time, are implemented from perturbation theory in a manner which smoothly interpolates between the strict next-to-leading order and the Landau-Pomeranchuk-Migdal regimes. By comparing the slope of the invariant mass spectrum with the average temperature of the fluid (at different evolution times), we assess the efficacy of this observable as a thermometer of the quark-gluon plasma (QGP). Furthermore, we are able to explore the capability of dileptons as a QGP `baryometer' via their sensitivity to the dynamical evolution and dissipation of baryon charge included in the simulations. We also investigate the correlation between the medium lifetime and the integrated dilepton yields in central and peripheral Au+Au collisions across the different beam energies. Finally, we compare the thermal dielectron invariant mass spectra with those from hadronic cocktail contributions and available STAR measurements. Our results provide a quantitative baseline for dilepton yields at BES energies and highlight the importance of this observable in probing features of QCD thermodynamics.
Photons provide snapshots of the evolution of relativistic heavy-ion collisions as they are emitted at all stages and do not interact with the medium strongly. Measurements of low momentum direct photons at PHENIX across different systems, from $p+p$, $p/d/^3$He$+$Au to Au$+$Au have been made possible due to the versatility of RHIC. An excess of direct photons, above prompt photon production from hard scattering processes and consistent with thermal photon emission is observed. The integrated yields scale as $(dN_{ch}/d\eta)^\alpha$, with $\alpha=1.12$, above multiplicities of 20-30. However, for systems with lower multiplicities, a gradual increase from $p+p$-like to $A+A$-like behavior is observed. In addition to the results for direct photon spectra for small and large collision systems, in this talk, azimuthal anisotropies of direct photons in Au$+$Au collisions at 200 GeV will also be presented, thereby, shedding light on the long-standing direct photon puzzle.
Measurements of direct photons provide valuable information on the properties of the quark-gluon plasma (QGP) because they are colour-neutral and created during all phases of the collision. Sources of photons include initial hard scatterings, Bremsstrahlung and the fragmentation process, jet-medium interactions, and radiation from the medium.
Direct thermal photons, produced by the plasma, are sensitive to the collective flow at photon production time. Their exponential spectral shape gives access experimentally to an effective medium temperature.
Furthermore, Bose-Einstein correlations can be used to study the space-time evolution of the medium created in heavy-ion collisions with Hanbury Brown and Twiss interferometry. The correlation function is sensitive to the source size and the direct photon fraction.
Direct prompt photons produced in hadronic collisions through annihilation and Compton processes have minimal event activity from the hard process, allowing the isolation method to suppress background photons from parton fragmentation and neutral meson electromagnetic decays.
Isolated photon measurements in pp and p--Pb collisions can constrain NLO pQCD predictions. Hadrons correlated with isolated photons are a promising channel to study the energy loss in heavy-ion collisions and to constrain the $Q^{2}$ of the initial hard scattering, obtaining information on the amount of energy lost by the parton recoiling off the photon.
The ALICE experiment reconstructs photons from conversion photons using its excellent tracking capabilities and directly in calorimeters. Combining these methods, ALICE can measure direct photons at mid-rapidity with transverse momentum from 0.4 GeV/$c$, where direct thermal photons should dominate until few GeV, then direct prompt photons take over and can be measured until about 100 GeV/$c$.
This talk presents ALICE measurements of direct-photon distributions using statistical (decay-photon subtraction, thermal photons) and isolation (prompt photons) methods in different collision systems and energies and their correlations.
Electromagnetic probes such as photons and dielectrons (e$^{+}$e$^{-}$ pairs) are a unique tool to study the space-time evolution of the hot and dense matter created in ultra-relativistic heavy-ion collisions. They are produced at all stages of the collision with negligible final-state interactions. At intermediate dielectron invariant mass ($m_{\rm ee} > 1$ GeV/$c^{2}$), thermal radiation from the quark-gluon plasma carries information about the early temperature of the medium. At LHC energies, it is however dominated by a large background from correlated heavy-flavour hadron decays. At smaller $m_{\rm ee}$, 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. Finally, at vanishing $m_{\rm ee}$, the real direct photon fraction can be extracted from the dielectron data. In pp collisions, such measurement in minimum bias events serves as a baseline and a fundamental test for perturbative QCD calculations, while studies in high charged-particle multiplicity events allow one to search for thermal radiation in small colliding systems. The latter show surprising phenomena similar to those observed in heavy-ion collisions.
In this talk, final ALICE results, using the full data sample collected during the LHC Run 2, will be presented. They include measurements of the dielectron and direct-photon production in central Pb--Pb at the centre-of-mass energy per nucleon pairs, $\sqrt{s_{\rm NN}}$, of 5.02 TeV, as well as of direct photons in minimum bias and high-multiplicity pp collisions at $\sqrt{s} = 13$ TeV. Finally, first results with the Run 3 pp data at $\sqrt{s} = 13.6$ TeV, using the upgraded ALICE detector to disentangle the different dielectron sources, will be reported.
Dielectrons emitted during the evolution of the hot and dense QCD medium created in relativistic heavy-ion collisions offer an effective way to probe the medium properties, as they do not interact via the strong force. The rate of the dielectron emission is proportional to the medium's electromagnetic spectral function. In the dielectron mass range from $400$ MeV/$c^{2}$ to $800$ MeV/$c^{2}$, the spectral function probes the in-medium $\rho$ meson propagator which is sensitive to the medium’s properties including the total baryon density and the temperature. Meanwhile, the low energy range of the spectral function provides information about the medium’s electrical conductivity. Therefore, by measuring thermal dielectron production, we can study the microscopic interactions between the electromagnetic current and the medium.
The STAR experiment has recorded large datasets of Au+Au collisions during the Beam Energy Scan Phase-II (BES-II) program, spanning center-of-mass energies ($\sqrt{s_{NN}}$) from 3.0 to 19.6 GeV with detector upgrades that benefit the dielectron measurement via extended transverse momentum and rapidity coverages as well as enhanced particle identification capability. In this talk, we will report on the measurements of thermal dielectrons produced in Au+Au collisions at $\sqrt{s_{\text{NN}}}=$ 7.7, 14.6, and 19.6 GeV using the STAR experiment.
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. Recent measurements of exclusive dielectron production in ultra-peripheral collisions (UPC) are presented. These processes provide strong constraints on the nuclear photon flux and its dependence on the impact parameter and photon energy. Comparisons of the measured cross-sections to QED predictions from the Starlight and SuperChic models are also presented. 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.
Heavy quarks, i.e. charm and beauty, are produced at the initial stage of heavy-ion collisions, on a time scale shorter than the medium formation time, and are sensitive to the large initial magnetic field produced perpendicular to the reaction plane (defined by the impact parameter direction and beam direction) in non-central heavy-ion collisions. In the presence of a large initial magnetic field, the charm quark can be polarised. The quark polarisation is expected to be transferred to the hadron in the hadronisation process. Experimentally, the heavy-flavour polarisation can be probed by measuring the spin density matrix element of spin 1 hadrons (as the $\rm{D}^{*+}$ meson). Any deviation of ρ00 parameter from ⅓ can be attributed to the spin alignment of $\rm{D}^{*+}$ meson.
We will present the first measurement of the $\rho_{00}$ parameter of $\rm{D}^{*+}$ meson in Pb–Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02~$TeV, exploiting the large data sample collected by the ALICE Collaboration during the LHC Run 2 in 2018. A comparison with the $J/\psi$ polarisation measurement will also be reported to investigate the effect of the magnetic field. In this study, one of the main background sources is represented by the feed-down contribution from B-meson decays, as vector mesons which decay from scalar B mesons are expected to be longitudinally polarized due to the helicity conservation in weak decays. In this context, the final measurement of the spin alignment of prompt and non-prompt $\rm{D}^{*+}$ mesons in pp collisions at $\sqrt{s}= 13~$TeV, used to quantify the effect of the feed-down in the Pb–Pb measurements, will be presented.
We study the hydrodynamization process in the aftermath of ultrarelativistic heavy-ion collisions using effective kinetic theory simulations and different observables. For the pressure ratio $P_T/P_L$, we observe that its late-time evolution becomes universal in units of the kinetic relaxation time for sufficiently large couplings signaling the onset of a hydrodynamical attractor. In contrast, at weak couplings, it converges earlier to a bottom-up attractor in terms of the thermalization time scale $\tau_{\text{BMSS}} = \alpha_s^{-13/5}/Q_s$. We interpret these as two limiting attractors. The dynamics of the occupancy of hard modes, the heavy-quark diffusion coefficient, and the jet quenching parameter are better described by a bottom-up limiting attractor even for moderate couplings. Therefore, the previous conjecture that the hydrodynamical attractor governs the late-time approach toward hydrodynamization is not complete. Our results rather indicate that a weak coupling attractor emerges additionally in the coupling regime relevant for heavy-ion collisions for certain observables.
Incoherent J/$\psi$ photoproduction is sensitive to fluctuations of the gluonic structure of the target. Thus, the measurement of $\rm{J/\psi}$ photoproduction off the colliding hadron sheds light on the initial state of QCD and provides important constraints on the initial conditions used in hydrodynamical models of heavy ion collisions. In this talk, we present the first measurement of the transverse momentum dependence of both coherent and incoherent $\rm{J/\psi}$ photoproduction in ultra-peripheral Pb-Pb collisions at mid-rapidity. These new results provide, for the first time, a clear indication of subnucleonic fluctuations of the lead target.
Hydrodynamic simulations of the quark-gluon plasma (QGP) permit us not only to gauge the transport properties of hot QCD matter from data, but also to constrain the conditions that set the stage for the formation of such matter. Recent measurements from RHIC and LHC demonstrate that the QGP initial condition is impacted by the shape and radial structure of the colliding nuclei. Based on a recent community white paper [1], we discuss physics opportunities for nuclear structure and QGP studies offered by high-energy nuclear collisions, with an emphasis on i) \textit{isobar collisions}, offering clean access to the structural properties of the colliding ions, as well as ii) collisions of bowling-pin-shaped 20Ne isotopes as a means to complement and broaden the hot QCD program envisaged via 16O+16O collisions. We argue that future experiments involving selected ion species will open new exciting directions of interdisciplinary research in nuclear science. Recent updates from the INT program [2] dedicated to this topic will also be covered.
[1] B. Bally \textit{et al.} ``Imaging the initial condition of heavy-ion collisions and nuclear structure across the nuclide chart,'' [arXiv:2209.11042 [nucl-ex]].
[2] "Intersection of nuclear structure and high‐energy nuclear collisions", 01/23/2023-02/24/2023, https://www.int.washington.edu/programs-and-workshops/23-1a
One of the main challenges in the theory of heavy ion collisions is understanding how an initial state of two highly Lorentz-contracted nuclei acquires the features of a hydrodynamic plasma in a characteristic time of 1 fm/c. Arguably, the most successful descriptions of this out-of-equilibrium stage have been established by finding so-called “attractor” solutions in the various (simplified) theories that attempt to capture out-of-equilibrium dynamics of QCD. These attractors are characterized by a loss of sensitivity to the initial conditions, which is achieved because the kinetic theory is dynamically driven to a preferred “attractor surface” in the phase space of the theory, often well before hydrodynamization in weakly coupled kinetic theory.
In this context, the adiabatic hydrodynamization framework [1,2] is a promising candidate to describe and characterize attractors in a model-independent formulation. In principle, all that needs to be done is to establish the dominance of an effective ground state in the dynamics of the system. This was done analytically in [2] for the first stage of the bottom-up thermalization scenario [3], demonstrating a dynamical reduction in the number of active degrees of freedom much earlier than the hydrodynamic regime. A key observation made in [2] was that such effective ground states may require a time-dependent change of coordinates for their dominance to be manifest. Ultimately, such a change of coordinates is one of the defining characteristics of the sought attractor solution, and therefore it becomes imperative to define a procedure to find the “optimal” coordinate transformation for a given theory. In this talk, we will lay out a candidate for such a procedure and will consider the example of collision-driven dynamics in the Bjorken-expanding kinetic theory of a dilute gluon gas to demonstrate the effectiveness of this method to describe attractor solutions. We will then lay out the path to explore more realistic descriptions of the expanding QGP, including the later stages of bottom-up thermalization, and the transverse expansion of the medium.
[1] Brewer, Yan, Yin, arxiv:1910.00021
[2] Brewer, Scheihing-Hitschfeld, Yin, arXiv:2203.02427
[3] Baier, Mueller, Schiff, Son, arXiv:hep-ph/0009237
The LHCb detector’s forward geometry provides unprecedented access to
the 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
neutral mesons, as well as relatively rare probes such as heavy quarks, providing
a unique set of constraints on nucleon structure functions. This contribution will
discuss recent LHCb measurements sensitive to the low-x structure of nucleons,
and discuss the impact of recent LHCb measurements that dramatically reduce
nPDF uncertainties.
There is increasing interest in using high-energy collisions to probe the structure of nuclei, in particular with the high-precision data made possible by collisions performed with pairs of isobaric species. A systematic study requires a variation of parameters representing nuclear properties such as radius, skin thickness, angular deformation, and short-range correlations, to determine the sensitivity of the various observables on each of these properties. In this work we propose a method for efficiently carrying out such study, based on the shifting of positions of nucleons in Monte-Carlo samples. We show that by using this method, statistical demands can be dramatically reduced --- potentially reducing the required number of simulated events by orders of magnitude --- paving the way for systematic study of nuclear structure in high-energy collisions.
As an application, we perform a systematic study of short-range nucleon-nucleon correlations and their effects on heavy-ion observables. Using our methods these effects, though small, can be precisely studied without the need for large numbers of simulations. In particular, we illustrate the limitations of a simple exclusion radius as a proxy for realistic nucleon-nucleon correlation functions.
Reference: arXiv:2302.14026
The study of thermal fluctuations in relativistic hydrodynamics is essential for understanding physics near the expected critical endpoint in the QCD phase diagram. Furthermore, the incorporation of stochastic fluctuations may be important for the modeling of hydrodynamics in small systems such as proton-proton and proton-nucleus collisions. We present a new general formalism for introducing thermal fluctuations in relativistic hydrodynamics which incorporates the recent developments on the causality and stability of relativistic hydrodynamic theories. Our approach is based on the recently introduced information current [1], which measures the net amount of information carried by perturbations around equilibrium in a relativistic many-body system. The resulting noise correlators are guaranteed to be observer-independent for thermodynamically stable models, which differs from previous approaches employed in the literature. We obtain a Martin-Siggia-Rose [2] action principle within our formalism and compare it to previous proposals for hydrodynamic effective actions. Finally, we present a few applications, which include the Israel-Stewart theory in a general hydrodynamic frame [3]. We find the adoption of a general hydrodynamic frame introduces new independent structures to the two-point function of the energy-momentum tensor which are not present in previous calculations done in the Landau or Eckart hydrodynamic frames.
[1] L. Gavassino, M. Antonelli, and B. Haskell, “Thermodynamic stability implies causality,” Physical Review Letters 128 (2022)
[2] P. C. Martin, E. D. Siggia, and H. A. Rose, “Statistical Dynamics of Classical Systems,” Phys. Rev. A 8, 423–437 (1973).
[3] Jorge Noronha, Michal Spali ́nski, and Enrico Speranza, “Transient relativistic fluid dynamics in a general hydrodynamic frame,” Physical Review Letters 128 (2022)
Unpolarized protons can generate transversely polarized quarks or linearly polarized gluons through a distribution known as the Boer-Mulders' function. The fragmentation of similarly polarized partons to unpolarized hadrons is called the Collins' function. Both of these functions include correlations between the spin or polarization and the relative transverse momentum of the incoming parton or outgoing hadron, with respect to the parent particle.
We explore the effect of including these and other TMDs on the production of high-$p_T$ (unpolarized) hadron production from (unpolarized) proton-proton scattering. The resulting initial state anisotropies, coupled with similar final state effects, may account for the observed azimuthal anisotropy of the produced high transverse momentum hadrons, without modification to the angle integrated spectra ($R_{AA} \simeq 1$). This may be an explanation for the existence of a $v_2$ in high-$p_T$ hadron spectra in $p$-$A$ collisions without any observable nuclear modification of the spectra.
We study cold nuclear matter effects on Drell-Yan production at small and moderate $p_T$ in proton/pion-nucleus collisions using a new transverse-momentum dependent (TMD) factorization framework. Both collisional broadening and medium-induced radiative corrections in the initial state are considered in the soft-collinear effective theory with Glauber gluons (SCET$_{G}$) approach. We demonstrate that in-medium bremsstrahlung exhibits rapidity divergences as $x\rightarrow 1$ and collinear divergences at the endpoints $x=0,1$ of the emission spectra. We further show that the rapidity divergences lead to Balitsky-Fadin-Kuraev-Lipatov (BFKL) evolution of the collision kernel and can be resummed into the transverse momentum broadening of particle production. In turn, the endpoints divergences of in-medium radiation can be resummed through the collinear evolution of parton densities in nuclear matter. The TMD factorization framework is applied to understand the transverse-momentum spectra of Drell-Yan pair production in $pA$ and $\pi A$ collisions and provides calculations with improved accuracy for hadron production in cold QCD processes at RHIC and LHC.
We study the boost-invariant non-conformal Boltzmann equation in the relaxation-time approximation using special moments of the distribution function and investigate how hydrodynamical behavior emerges as the plasma transits from the far-off-equilibrium free-streaming regime to the hydrodynamic regime. The infinite hierarchy of moments can be truncated by keeping only the three lowest moments that correspond to the three independent components of the energy-momentum tensor. By comparing the moment equations with the Israel-Stewart hydrodynamic equations, we demonstrate that the latter are able to capture the early-time, collisionless dynamics, albeit approximately, due to their relaxation-type structure [1]. We also derive second-order non-conformal hydrodynamics from the three-moment truncation and find that there are ambiguities in the definition of some second-order transport coefficients. In order to understand the nature of these ambiguities, we derive the full second-order non-conformal hydrodynamics by employing Chapman-Enskog expansion and also from a novel entropy approach and show that such ambiguities are inherent when defining some of the second-order transport coefficients [2]. We show that these ambiguities affect the ability of the Israel-Stewart hydrodynamics to reproduce the results of kinetic theory. The implications of these results in the context of heavy-ion collisions will be discussed.
[1] From moments of the distribution function to hydrodynamics: The nonconformal case, S. Jaiswal, J. P. Blaizot, R. S. Bhalerao, Z. Chen, A. Jaiswal and L. Yan, Phys. Rev. C 106, 044912 (2022)
[2] Shear-bulk coupling in second-order viscous hydrodynamics, S. Jaiswal, J. P. Blaizot (in preparation)
We propose a method to find local plane wave solutions to linearized equations of motion of relativistic hydrodynamics in inhomogeneous backgrounds, i.e., when fluid is rigidly moving with nonzero thermal vorticity in equilibrium. Our method is based on extending the conserved currents to the tangent bundle, using Wigner transforms. The Wigner-transformed conserved currents can then be Fourier transformed into the cotangent bundle to obtain the dispersion relations for space-time-dependent eigenfrequency. We show that the connection between the stability of hydrodynamics and the evolution of plane waves is not as straightforward as in the homogeneous case and is restricted to the equilibrium-preserving subspace of the cotangent bundle, which is determined by thermal vorticity. We apply this method to MIS theory and show that the interplay between the bulk viscous pressure and the shear stress tensor with acceleration and rotation leads to novel modes, as well as modifications of the already known ones.
Determining the existence and the location of the QCD critical point remains a major goal in the heavy-ion collision experiments. A crucial theoretical input for achieving this goal is mapping the QCD equation of state in the presence of baryon chemical potential (mu) which at the moment is limited to small values of mu, away from the critical point. I present a new framework for reconstructing the equation of state from a truncated Taylor series expansion for small mu by using novel resummation techniques. I show how this resummation method can be used to (i) determine the location of the critical point and (ii) constrain the form of the critical contribution to the QCD equation of state which has a direct impact on the shape of the experimental signatures of the critical point.
We investigate whether early and late time attractors for non-conformal kinetic theories exist by computing the time-evolution of a large set of moments of the one-particle distribution function. For this purpose we make use of a previously obtained exact solution of the 0+1D boost-invariant massive Boltzmann equation in relaxation time approximation. We extend prior attractor studies of non-conformal systems by using a realistic mass- and temperature-dependent relaxation time and explicitly computing the effect of varying both the initial momentum-space anisotropy and initialization time on the time evolution of a large set of integral moments. Our findings are consistent with prior studies, which found that there is an attractor for the scaled longitudinal pressure, but not for the shear and bulk viscous corrections separately. We further present evidence that both late- and early-time attractors exist for all moments of the one-particle distribution function that contain greater than one power of the longitudinal momentum squared.
Sixth and higher order fluctuations of the baryon number are linked
to signals of criticality in heavy ion collisions. The grand canonical
result for these can be obtained from lattice simulations. The
extrapolation to the continuum limit is essential for phenomenologically
relevant results. In fact, higher order coefficients of the Taylor
expansion of the QCD free energy appear to be more sensitive to
discretization effects than lower orders. We meet the challenge in a
modest volume using the new 4HEX fermion action and calculate
the sixth order cumulants in a continuum extrapolation.
Our study presents a family of Equations of State (EoS) that enable hydrodynamical simulations at unprecedentedly large baryon chemical potential ($\mu_B$) and finite temperature ($T$), thus helping to constrain the critical point's location by comparing it to experimental data from the Second Beam Energy Scan.
In Ref. [1], a family of equations of state was constructed by combining Taylor expansion QCD lattice results with 3D Ising model critical behavior. However, the applicability of this family was limited to the range of $ 0 \leq \mu_B \leq 450$ MeV. In recent work, [2,3], a resummation scheme was proposed that extrapolates lattice QCD results to the range of chemical potentials $\frac{\mu_B}{T} = 3.5 $.
In this work, we combine these approaches to obtain equations of state in the range $0 \leq \mu_B \leq 700$ MeV and 5 MeV $\leq T \leq 800$ MeV, which match lattice QCD results at low density and contain a 3D Ising model critical point. We impose stability and causality constraints and discuss the possible ranges of free parameter choices arising from the 3D Ising model to QCD mapping. We present thermodynamic observables, including baryon density, pressure, entropy, energy density, susceptibility, and speed of sound that cover a wide range in the QCD phase diagram.
[1] P. Parotto, M. Bluhm, D. Mroczek, M. Nahrgang, J. Noronha-Hostler,
K. Rajagopal, C. Ratti, T. Sch ̈afer, and M. Stephanov, “Qcd equation of
state matched to lattice data and exhibiting a critical point singularity,”
Physical Review C, vol. 101, no. 3, p. 034901, 2020. 1
[2] S. Bors ́anyi, J. N. Guenther, R. Kara, Z. Fodor, P. Parotto, A. P ́asztor,
C. Ratti, and K. Szab ́o, “Resummed lattice qcd equation of state at finite
baryon density: Strangeness neutrality and beyond,” Physical Review D,
vol. 105, no. 11, p. 114504, 2022. 1
[3] S. Bors ́anyi, Z. Fodor, J. Guenther, R. Kara, S. Katz, P. Parotto, A. P ́asztor,
C. Ratti, and K. Szab ́o, “Lattice qcd equation of state at finite chemical
potential from an alternative expansion scheme,” Physical review letters,
vol. 126, no. 23, p. 232001, 2021. 1
2
This talk will present the Bayesian inference approach for quantitatively characterizing the 3D dynamics of heavy-ion collisions and the Quark-Gluon Plasma (QGP) properties in the RHIC Beam Energy Scan (BES) program. To model the dynamics of the collisions from 7.7 to 200 GeV, we employ a (3+1)D dynamical initialization model coupled with the relativistic viscous hydrodynamics + hadronic cascade hybrid framework [1]. To account for shear and bulk viscous effects at RHIC BES energies, we derive the out-of-equilibrium corrections to particle distributions with multiple conserved charge currents using Grad's moment and Chapman-Enskog methods. A fast model emulator is then trained in a 22-dimensional parameter space to accurately predict identified particle yields, average transverse momenta, and charged hadron anisotropic flow coefficients. By carrying out a joint Bayesian analysis of the RHIC BES phase I measurements for Au+Au collisions at 7.7, 19.6, and 200 GeV, we set robust constraints on initial-state baryon stopping and the $\mu_B$ and $T$ dependence of the QGP shear and bulk viscosity. Our results show that the Bayesian inference approach with our full (3+1)D hybrid framework effectively extracts the QGP properties and the 3D dynamics of the collision events from the RHIC BES measurements and provides quantitative insights into the QCD matter in a baryon-rich environment.
[1] C. Shen and B. Schenke, "Longitudinal dynamics and particle production in relativistic nuclear collisions," Phys. Rev. C105, no.6, 064905 (2022)
Quantum Chromodynamics (QCD), the theory of strong interactions, predicts that at sufficiently high temperature and/or high energy density, normal nuclear matter converts into a deconfined state of quarks and gluons, known as the Quark-Gluon Plasma (QGP). To investigate the phase diagram of the QCD matter, the Relativistic Heavy Ion Collider (RHIC) started the first phase of the Beam Energy Scan (BES-I) program in 2010, delivering Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7 to 62.4 GeV. The success of the BES-I program justified the second phase of Beam Energy Scan (BES-II) with higher statistics and detector upgrades. Au+Au collisions at $\sqrt{s_{\text{NN}}}$= $7.7-54.4$ $\text{GeV}$ were collected during $2017-2021$, covering a large area of the QCD phase diagram in temperature and baryon chemical potential by varying the collision energy, centrality, and rapidity. In particular, the installed Event Plane Detector (EPD) enables the measurement of charged particle production at far-backward pseudorapidity.
In this talk, we present pseudorapidity distributions of charged particles in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7 to 27 GeV with the EPD ($2.15 < |\eta| < 5.09$). We will also present the transverse momentum spectra of identified hadrons ($\pi^{\pm}$, $K^{\pm}$, $p$ and $\bar{p}$) in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7 to 54.4 GeV within mid-rapidity ($|y| < 1$). The mid-rapidity yields of identified hadrons show the expected signatures of large baryon stopping at lower energies and the dominance of pair production at higher energies. The centrality dependence of integrated yields (dN/dy and dN/d$\eta$), average transverse momenta ($\langle p_{T} \rangle$), particle ratios, chemical and kinetic freeze-out parameters will also be presented. These results will be compared to published results at other collision energies and the new insights to the QCD phase diagram will be discussed.
The equation of state of the quark gluon plasma is a key ingredient of heavy ion phenomenology. In addition to the traditional Taylor method, several novel approximation schemes have been proposed with the aim of calculating it at finite baryon density. In order to gain a pragmatic understanding of the limits of these schemes, we compare them to direct results at $\mu >0$, using reweighting techniques free from an overlap problem. We use 2-stout improved staggered fermions with 8 time-slices and cover the entire RHIC BES range in the baryochemical potential, up to $\mu_B/T=3$.
The equation of state of Quantum Chromodynamics has been in recent
years the focus of intense effort from first principle methods,
mostly lattice simulations, with particular interest to the finite
baryon density regime. Because of the sign problem, various
extrapolation methods have been used to reconstruct bulk properties
of the theory up to as far as $\mu_B/T \simeq 3.5$. However, said
efforts rely on the equation of state at vanishing baryon density
as an integration constant, which up to $\mu_B/T \simeq 2 - 2.5$
proves to be the dominant source of uncertainty at the level of
precision currently available. In this work we present the update of
our equation of state at zero net baryon density from 2014, performing
a continuum limit from lattices with $N_\tau=8,10,12,16$. We show
how the improved precision is translated in a lower uncertainty on
the extrapolated equation of state at finite chemical potential.
Heavy quarks are produced in the early stages of the ultra-relativistic heavy-ion collisions and probe the produced hot medium created in these collisions through its entire evolution. The kinetic thermalization of heavy quarks can be characterized by the heavy quark diffusion coefficient. In this talk we report the first determination of the heavy diffusion coefficient in 2+1 flavor lattice QCD in temperature range 195 <T< 352 MeV using the heavy quark effective theory approach combined with novel gradient flow technique. We found that our full QCD determinations are significantly smaller than the quenched lattice QCD determinations and recent phenomenological estimates, implying a very fast kinetic thermalization the heavy quarks. Within this approach we also estimate the first mass suppressed correction to the diffusion coefficient for the first time in 2+1 flavor QCD for the above temperature range.
High-energy jets are produced by the fragmentation of partons (quarks and gluons) that underwent hard scattering in the early stages of a collision. For quite a number of years, jets have been successfully used to probe the properties of the special form of matter, the quark gluon plasma (QGP), formed in high-energy heavy ion collisions. One of the most recognized signatures of the QGP, the jet quenching phenomenon, has been evidenced by a wide range of LHC measurements from lead-lead collisions. More recently, experimental results through multiparticle correlation techniques provided some evidence of possible QGP formation in the smaller colliding systems, such as high-multiplicity proton-proton and proton-lead collisions, but confirmation of the jet quenching expected for QGP remains elusive for such collisions. In this talk, systematic measurements of jet properties are presented for proton-lead collisions data collected by the CMS experiment to search for hot medium production or effects of cold nuclear matter in small systems. Using the subevent cumulant method, multiparticle correlations are also measured for particles with high transverse momentum.
While the formation of the quark--gluon plasma (QGP) in heavy-ion collisions has been confirmed by characteristic patterns of flow measurements, it remains unclear what is the smallest possible collision system that can generate a similar medium exhibiting partonic collectivity. In this talk, we will present the new preliminary results of anisotropic flow in pp, p--Pb, and Pb--Pb collisions that, for the first time, encompass all the data collected by ALICE. The highlights include the flow of charged and identified particles ($\pi^{\pm}$, K$^{\pm}$, p ($\overline{\rm {p}}$), K$^0_S$, $\Lambda$ ($\overline \Lambda$), $\varphi$), correlations and fluctuations of flow vectors and correlations between the mean transverse momentum and flow coefficients, $\rho(v_n^2,[p_\mathrm{T}])$. Multiparticle cumulants with the subevent method, ultra-long-range azimuthal correlations with the template fit method, and a novel jet veto approach have been implemented to effectively suppress short-range non-flow contamination. We compare our results to state-of-the-art theoretical models, which will allow us to study contributions from initial momentum anisotropies to final anisotropic flow, and to understand how anisotropic flow in small collision systems developed from the initial geometry through the dynamic evolution including the understanding of the role of mass and constituent-quark numbers.
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, intermediate to previous fixed-target experiments and the top
RHIC energy for AA collisions, and allow systems of different size to be stud-
ied. Here we present new results on open charm, J/ψ, and ψ(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
The JETSCAPE Collaboration reports new studies of jet transport in the QGP using Bayesian Inference, incorporating both hadron and jet inclusive yield suppression data, and jet substructure data. This analysis extends the previously published JETSCAPE Bayesian determination of $\hat{q}$, which was based solely on inclusive hadron suppression data.
JETSCAPE is a modular framework for multi-stage modeling of in-medium jet evolution and medium response, with rigorous data-model comparison using a Bayesian formalism. The theoretical model in the current study utilizes virtuality-dependent in-medium partonic energy loss coupled to a detailed dynamical model of QGP evolution.
The $\hat{q}$ analysis presented in this talk includes, for the first time, all reported hadron and jet inclusive yield suppression measurements at RHIC and the LHC. The uncertainty covariance of the data is estimated, where not reported. We explore the tension in this determination of $\hat{q}$ between the hadron and the various jet measurements, and between different kinematic regions. In addition we examine the additional information that jet substructure observables provide beyond that contained in inclusive jet and hadron suppression observables. These studies provide new insight into the mechanisms of jet interactions in matter, and point to next steps in the field for comprehensive understanding of jet quenching as a probe of the QGP.
We will present the final measurement studying the relationship between the production of hard and soft particles through the correlation of Upsilon meson states (including $\Upsilon$(1S), $\Upsilon$(2S), and $\Upsilon$(3S)) with the inclusive-charged particle yields. The analysis is performed using the full-luminosity ATLAS Run-2 13 TeV $pp$ collision data. A description of the technical challenges and solutions associated with a heavy-ion style analysis in high-pileup $pp$ data will be shown. Per-event charged particle multiplicity is found to be smaller in association with excited $\Upsilon$ states compared to that with a ground state at low $\Upsilon$ transverse momentum. The physics implications will be discussed.
Employing a dynamical initial state model coupled to (3+1)D viscous relativistic hydrodynamics, we explore the rapidity dependence of anisotropic flow in the Relativistic Heavy-Ion Collider (RHIC) small system scan at 200 GeV center of mass energy. We demonstrate that approximately 50% of the pT-differential triangular flow difference between the measurements by the STAR and PHENIX Collaborations can be explained by the use of reference flow vectors from different rapidity regions. This emphasizes the importance of longitudinal flow decorrelation for anisotropic flow measurements in asymmetric nuclear collisions, and the need for (3+1)D simulations. We further present results for the beam energy scan of d+Au collisions and compare to PHENIX data. The same framework is used to describe p+Pb collisions and photo-nuclear events in ultra-peripheral Pb+Pb collisions at the Large Hadron Collider (LHC). We compare to experimental data on momentum anisotropies from the ATLAS Collaboration and find good agreement with the measured elliptic flow. Again, the importance of longitudinal flow decorrelations is highlighted, as they dominate the elliptic flow hierarchy between p+Pb and γ+Pb collisions. Our results imply that QCD fluids can be created at the future Electron Ion Collider, where they could be studied in great detail.
References:
3D structure of anisotropic flow in small collision systems at energies available at the BNL Relativistic Heavy Ion Collider
Wenbin Zhao, Sangwook Ryu, Chun Shen, Björn Schenke
e-Print: 2211.16376 [nucl-th] DOI: 10.1103/PhysRevC.107.014904
Published in: Phys.Rev.C 107 (2023) 1, 014904
Collectivity in Ultraperipheral Pb+Pb Collisions at the Large Hadron Collider
Wenbin Zhao, Chun Shen, Björn Schenke
e-Print: 2203.06094 [nucl-th] DOI: 10.1103/PhysRevLett.129.252302
Published in: Phys.Rev.Lett. 129 (2022) 25, 252302
Collectivity in small systems is a crucial area of study in high-energy nuclear physics, as it provides valuable insights into initial conditions and pre-equilibrium stages in heavy-ion collisions. The small system collision scan at RHIC, including both symmetric and asymmetric small systems (O+O $>$ $^{3}$He$+$Au $>$ $d$$+$Au $>$ $p$$+$Au $>$ $\gamma+$Au), provides a better understanding of how collectivity emerges and evolves with system size.
We analyze a large sample of minimum bias and central triggered $^{16}$O+$^{16}$O collisions at $\sqrt{s_{NN}}$ = 200 GeV and inclusive $\gamma$+Au processes (center-of-mass energy around 40 GeV) by triggering ultra-peripheral events in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. Using two- and four-particle correlation methods, we present the first measurements of azimuthal anisotropies, $v_2$ and $v_3$, in $^{16}$O+$^{16}$O and $\gamma$+Au collisions as a function of $p_{\mathrm{T}}$ and multiplicity. We compare our measurements with STAR measurements of $v_n$ in $p/d/^3$He+Au collisions and hydrodynamic model calculations.
New $v_{n}$ measurements in $^{16}$O+$^{16}$O collisions provide insight into the impact of system symmetry on initial condition and pre-equilibrium dynamics, compared to the previously studied asymmetric systems $p/d/^3$He+Au. We also investigate the ratio $v_2\{4\}/v_2\{2\}$ and correlations between $v_n$ and mean $p_{\mathrm{T}}$ as a function of multiplicity, which are sensitive to initial momentum anisotropy, subnucleon fluctuations, and clustering in the $^{16}$O nucleus. In addition, $v_{n}$ measurements in $\gamma$+Au processes play an important role in understanding the origin of collectivity and lay the foundation for searching for many-body systems exhibiting collective behavior in photon-induced processes at the EIC.
Two-particle correlations are presented for $\mathrm{K^{0}_S}$, $\Lambda$, and $\bar{\Lambda}$ strange hadrons as a function of relative momentum in lead-lead (PbPb) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV with data samples collected by the CMS experiment. These correlations are sensitive to quantum statistics and to final-state interactions between particles. The $\Lambda\Lambda$ femtoscopic correlation is measured for the first time in PbPb collisions. It is seen that the shape of the correlation distributions varies largely for different particle pair species, revealing the effect of the strong final-state interaction in each case. The source size extracted from the $\mathrm{K^{0}_S}\mathrm{K^{0}_S}$ correlations is found to decrease from 4 to 1 fm in going from central to peripheral collisions. Strong interaction scattering parameters (i.e. scattering length and effective range) are determined from the $\Lambda\mathrm{K^{0}_S}$ and $\Lambda\Lambda$ (including their charge conjugates) correlations using the Lednicky--Lyuboshitz model and are compared to theoretical and other experimental results.
Recent measurements of the production of charm hadrons at midrapidity in pp collisions at $\sqrt s$ = 5.02 and 13 TeV showed that the baryon-to-meson yield ratios are significantly larger than those measured in $\rm e^{+}e^{-}$ collisions for different charm-baryon species. These observations suggest that the charm fragmentation fractions are not universal and that the baryon-to-meson ratios depend on the collision systems.
In this poster, the new measurement of the inclusive $p_{\rm T}$-differential cross section of the charm-strange baryon $\Omega_{\rm c}^{0}$ multiplied by the branching ratio of the $\Omega_{\rm c}^{0} \rightarrow \rm \Omega^{-}\pi^{+}$ decay channel in pp collisions at $\sqrt s$ = 13 TeV will be reported, and compared with theoretical calculations.
However, the lack of absolute measurements of the $\Omega_{\rm c}^{0}$ branching ratios makes it difficult to draw conclusions about the effective $\Omega_{\rm c}^{0}$ enhancement. To address this, a new analysis of the $\Omega_{\rm c}^{0}$ reconstructed from the $\rm e^{+}\Omega^{-}\nu_{e}$ decay channel is being performed, and its status and developments will be also discussed.
Two-particle correlations are used to extract the space-time and dynamical information of the particle-emitting source created in heavy-ion collisions. The source radii extracted from these correlations characterize the system at the kinetic freeze-out, i.e., the last stage of particle interactions. Kaons can provide a more direct view of the particle-emitting source than pions as they have smaller hadronic cross section and less contribution from long lifetime resonances.
In this poster, the measurements of $K^{+}K^{+}$ correlation functions in Au+Au collisions at $\sqrt{s_{NN}}$ = 3.0, 3.2, 3.5, and 3.9 GeV recorded by the STAR experiment will be presented. One-dimensional source size $(R_{inv})$ and correlation strength parameter ($\lambda$) of the system are extracted from the correlation functions using the Bowler-Sinyukov formula. The comparison of the measured radii with the predictions from UrQMD+CRAB will be discussed.
Based on the fact that the mass difference between the chiral partners is an order parameter of chiral phase transition and that the chiral order parameter reduces substantially at the chemical freeze-out point in ultra-relativistic heavy ion collisions, we argue that the production ratio of K1 over K∗ in such collisions should be substantially larger than that predicted in the statistical hadronization model. We further show that while the enhancement effect might be contaminated by the relatively larger decrease of K1 meson than K∗ meson during the hadronic phase, the signal will be visible through a systematic study on centrality as the kinetic freeze-out temperature is higher and the hadronic life time shorter in peripheral collisions than in central collisions.
Jet-induced medium response is in the form of Mach-cone-like excitation. Diffusion wake accompanying this 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 $\gamma$-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 increase with the azimuthal angle away from the jet. It is also found to deepen with the jet energy loss as characterized by the $\gamma$-jet asymmetry. Its sensitivity to medium properties such as the shear viscosity and equation of state is also studied.
The Electron-Ion Collider (EIC) at Brookhaven National Laboratory will be an experimental facility to explore gluons in nucleons and nuclei, shedding light on their structure and the interactions within. The ePIC detector will be the first experiment at the EIC dedicated to detailed studies of nuclear structure in electron-proton and electron-ion collisions.
The ambitious physics program of the EIC requires a high performance hadronic calorimetry system in the hadron-going “forward” region. Accurate jet measurements are crucial to reconstruct the full 3D nucleon tomography and to study the gluon saturation region. The main goal of the Longitudinally segmented Forward HCal (lf-HCal) is measuring the energies of jets and distinguishing between overlapping jet depositions to high accuracy in the jet energy range up to 120 GeV.
lf-HCal is designed as a plastic scintillator-steel sandwich calorimeter. The plastic scintillator is transversely segmented into $5\times5$,cm${}^2$ tiles. Each tile is directly coupled to a silicon photomultiplier. The electrical signals of all photomultipliers are routed out of the lf-HCal to be digitized by external readout electronics.
This poster will present the current status as well as ongoing and future R&D of the lf-HCal for the ePIC experiment.
In this contribution, we extend the scope of the JETSCAPE framework to cover the jet radius ($R$) dependence of the jet nuclear modification factor, ${R_{AA}}$, for broader area jet cones, going all the way up to $R$ = 1.0. The primary focus of this work has been the in-depth analysis of the high-${p_{T}}$ inclusive jets and the quenching effects observed in the quark-gluon plasma formed in the Pb-Pb collisions at ${\sqrt{\rm s_{NN}}}$= 5.02 TeV for the most-central (0-10%) collisions. The nuclear modification factor is calculated for inclusive jets to compare with the experimental data from the ATLAS and CMS detectors in the jet transverse momentum (${p_{T}}$) ranging from 100 GeV up to 1 TeV. The results predicted by the JETSCAPE are consistent in the high ${p_{T}}$ range as well as for extreme jet cone sizes within 10-20\%. We also calculate the double ratio (${R^{\mathrm{R}}_{\mathrm{AA}}/R^{\mathrm{R=small}}_{\mathrm{AA}}}$) as a function of jet radius and jet-${p_{T}}$, where the observations are well described by the JETSCAPE framework which is based on the hydrodynamic multi-stage evolution of the parton shower. The calculations are then performed for low-virtuality-based evolution models like the MARTINI and the AdS/CFT, followed by a rigorous comparison between the former model's predictions and the CMS experiment's measurements.
Electromagnetic radiation is emitted throughout the whole evolution of high-energy heavy-ion collisions. Due to their penetrating nature, real and virtual photons reach the detector unimpeded. Their measurement makes it possible to shed light on the different stages of the extreme states of matter created in such collisions.
In this poster, we will discuss dielectron measurements that will only be possible with a new generation's experiment at the LHC and the features of the ALICE 3 detector that will enable them. In particular, the rejection of dielectrons from correlated semi-leptonic decays of heavy-flavour hadrons will be evaluated. We will present the expected performance of differential measurements of the thermal emission of dielectrons and the derived early-time temperature of the medium. The unique possibility to probe the pre-hydrodynamic phase of the medium with $\rm e^{+}e^{-}$ pairs will be discussed. In addition, the capability for detailed studies of chiral symmetry restoration mechanisms with a precise measurement of the rho spectral function will be addressed.
We elucidate the relationship between Color Glass Condensate (CGC) and Higher-twist (HT) formalisms at the level of physical observables by studying the direct photon production in proton-nucleus collisions. The CGC effective theory and the HT factorization theorem are two established formalisms that describe multiple scatterings of quarks and gluons in nuclear media within Quantum Chromodynamics (QCD). These formalisms have distinct domains of validity in kinematic regions. Going beyond the shock wave approximation and considering the Landau-Pomeranchuk-Migdal effect, which arises from the interference of initial- and final-state scatterings, we show for the first time that CGC and HT formalisms can be unified to describe the same physics in the transition region where they overlap. This unified picture provides a framework for understanding the QCD dynamics in the transition from dilute to dense nuclear matter, paving the way for mapping out the QCD evolution phase diagram of nuclear medium from dilute to dense region. This study highlights the importance of sub-eikonal phases in accurately describing multiple scatterings in nuclear media and sheds new light on the interplay between HT and CGC formalisms.
We demonstrate that the early stages of the bottom-up thermalization scenario [1] are well described by the adiabatic hydrodynamization framework, thus providing novel analytic results on the thermalization process of QCD in a heavy ion collision. These results provide an intuitive explanation of why a gas of quarks and gluons can relax so quickly towards equilibrium, and provide a starting point for a systematic exploration of pre-hydrodynamic attractors in QCD. All of the qualitative features exhibited in QCD effective kinetic theory (EKT) simulations at weak coupling [2] are captured by the emergence of an effective low-energy instantaneous ground state for the 1-particle gluon distribution function, which defines the early-time kinetic theory attractor. This ground state may be pulled back to arbitrarily early times, where it represents a free-streaming solution, and at later times it integrally describes the BMSS fixed point, including the recently observed deviations from the original predictions for the scaling exponents [2].
To find this instantaneous ground state it is necessary to elucidate the deep connections between scaling and adiabaticity in expanding gluon plasmas [3]. We first solve the Boltzmann equation for gluons in the small-angle scattering approximation numerically and find that it features time-dependent scaling, reproducing the QCD EKT scaling of hard gluons [2]. By studying this equation analytically, we find that an appropriate momentum rescaling allows the scaling distribution to be identified as the instantaneous ground state of the operator describing the evolution of the distribution function, and the approach to the scaling function is described by the decay of the excited states. That is to say, the system evolves adiabatically, and the instantaneous ground state describes the early-time kinetic theory attractor. We obtain this ground state analytically. Corrections to the BMSS fixed point exponents agree quantitatively with those found previously in QCD EKT.
[1] Baier, Mueller, Schiff, Son, arXiv:hep-ph/0009237
[2] Mazeliauskas, Berges, arXiv:1810.10554
[3] Brewer, Scheihing-Hitschfeld, Yin, arXiv:2203.02427
The production of deuterons in pp collisions at $\sqrt{s}=$ 13 TeV is simulated on an event-by-event basis using a coalescence afterburner based on a state-of-the-art Wigner-function formalism, and EPOS 3 and PYTHIA 8.3 as event generators. The space-momentum correlations of the nucleon pairs provided by the event generators are preserved, while the nucleon-emitting source is modelled such to reproduce the $m_{\rm T}$-dependence of the source size measured by ALICE. For the first time, the results of this model show that using a realistic wavefunction for deuterons, namely Argonne $v_{18}$, it is possible to reproduce the measured deuteron spectra with no free parameters.
Hypernuclei are bound states of nucleons and hyperons. The study of their properties, such as their lifetimes and binding energies, provide information on the hadronic interaction between hyperons and nucleons which are complementary to those obtained from correlation measurements. Precise modeling of this interaction is a fundamental input for the calculation of the equation of state of high-density nuclear matter inside neutron stars. Moreover, measurements of their production rate in different collision systems are important to constrain (hyper)nuclei production models, such as the statistical hadronization model and baryon coalescence.
In this presentation, the first-ever observations of the (anti)hyperhydrogen-4 and (anti)hyperhelium-4 in Pb--Pb collisions at 5.02 TeV will be presented. These measurements pave the way for detailed investigations of the large charge symmetry breaking implied by the Λ binding energy difference in these hypernuclei. Moreover, differential measurements of their productions yields will contribute to a better understanding of their production models. Recent results on the hypertriton production, high-precision measurements of its lifetime and binding energy in Pb--Pb collisions will also be shown and discussed in the context of the state-of-the-art theoretical models.
The spin alignment of vector mesons emitted in heavy-ion collisions has recently been measured by the ALICE and STAR collaborations over a wide range of energies [1, 2]. The alignment is part of the so-called tensor polarization, which is a property that is exclusive to particles of spin 1 and higher. Even though there have been substantial theoretical efforts, a definite explanation for the tensions between theory and experiments does not yet exist.
In this work [3], we derive an expression for the tensor polarization of a system of massive spin-1 particles in a hydrodynamic framework. Starting from quantum kinetic theory based on the Wigner-function formalism, we employ a modified method of moments which also takes into account all spin degrees of freedom. We find that the tensor polarization is independent of the nonlocal part of the collision term and sourced by the usual dissipative quantities of the fluid, i.e., the bulk-viscous pressure, the particle-diffusion current, and the shear-stress tensor. As an example, we compute the relevant transport coefficient in the case of an uncharged fluid, where, neglecting bulk effects, the tensor polarization is determined solely by the shear-stress tensor. In order to quantify this polarization effect, we provide a formula which can be used for numerical calculations of vector-meson spin alignment in relativistic heavy-ion collisions.
[1] S. Acharya et al. (ALICE), Phys. Rev. Lett. 125, 012301 (2020), 1910.14408.
[2] M. Abdallah et al. (STAR), Nature 614, 7947 (2023), 2204.02302.
[3] D. Wagner, N. Weickgenannt, E. Speranza, Phys. Rev. Res. 5, 013187 (2023), 2207.01111.
The tracking system of the sPHENIX detector at RHIC consists of three layers of MAPS based silicon pixel detectors for precise vertex determination, two layers of silicon strip detectors for pattern recognition and beam crossing determination, a TPC for precise momentum measurement, and a partial coverage micromegas detector to assist with calibration of space charge distortions in the TPC. The physics program of sPHENIX imposes stringent requirements on the precision of both the displaced vertex measurement and the momentum resolution. Meeting those requirements demands precise alignment of the four tracking subsystems. This poster describes the alignment process for the sPHENIX tracking system. The sPHENIX detector is taking data for the first time during the 2023 RHIC run, and the status of the alignment at the time of the conference will be presented.
The quark-hadron transition that happens in ultra-relativistic heavy-ion collisions is expected to be influenced by the effects of rotation and magnetic field, both present due to the geometry of a generic non-head-on impact. We augment the conventional $ T$--$\mu_B$ planar phase diagram for QCD matter by extending it to a multi-dimensional domain spanned by temperature $T$, baryon chemical potential $\mu_B$, external magnetic field $B$ and angular velocity $\omega$. Using two independent approaches, one from a rapid rise in entropy density and another dealing with a dip in the speed of sound, we identify deconfinement in the framework of a modified statistical hadronization model. We find that the deconfinement temperature $T_C(\mu_B,\omega,eB)$ decreases nearly monotonically with increasing $ \mu_B, \omega $ and $ eB $ with the most prominent drop (by nearly $40$ to $50$ MeV) in $T_C$ occurring when all the three quasi-control (collision energy and impact parameter dependent) parameters are simultaneously tuned to finite values that are typically achievable in present and upcoming heavy-ion colliders.
We develop an implicit numerical method for solving relativistic hydrodynamics that can be more efficient than conventional explicit methods. While implicit Runge-Kutta methods have nice properties such as their stability, they are not used usually since they are generally considered to be computationally expensive. In the present study, we solve this problem by introducing a fixed-point solver for the implicit Runge-Kutta methods with several optimizations. The Kurganov-Tadmor scheme is employed for the space discretization. The accuracy and computational cost of our new method are compared with those of explicit ones with the same space scheme in the case of ideal hydrodynamics for the initial conditions of the Riemann problem and the Gubser flow, as well as the event-by-event initial conditions for heavy-ion collisions generated by TRENTo. We demonstrate that the solver converges with only one iteration in most cases, and as a result, contrary to the general expectation, the implicit method requires smaller computational cost than the explicit one at the same accuracy in these cases.
We present an innovative procedure to account for unavoidable contributions from volume (or system size) fluctuations to experimentally measured cumulants of particle multiplicity distributions produced in relativistic nuclear collisions. For the first time we extract participant fluctuations directly from the data used for the fluctuation analysis, i.e., without involving model calculations [1]. To achieve this we exploit a dedicated event-mixing algorithm. Participant fluctuations are extracted by constructing cumulants of multiplicity distributions for different particle species and covariances between all possible pairs of particles. A detailed procedure for evaluating the precision of the method for different experiments, such as STAR at RHIC/BNL and HADES GSI/SIS18 will be discussed. The proposed method is essential for analyzing fluctuation signals at low collision energy, but can be applied at LHC energy as well.
[1] A. Rustamov, R. Holzmann, J. Stroth Nucl.Phys. A 1034 (2023) 122641
We investigate the critical fluctuations in light-nuclei production in heavy-ion collisions based on the coalescence model, where we introduce corrections to the distribution function from critical correlators from the Ising model.
The measurement of the yield ratio of light nuclei, $N_tN_p/N^2_d$ (with $N_t$, $N_p$, and $N_d$ being triton, proton, and deuteron numbers, respectively), in STAR collaboration [1], has shown a non-monotonic behavior as a function of collision energy in a heavy-ion collision. Based on the analyses with idealized setups, it was also suggested that the yield ratio is one of the observables for a possible signal of the QCD critical point [2]. However, it is non-trivial how the yield ratio is affected by the other contributions in realistic setups of heavy-ion collisions. In our previous study, we expanded the distribution function of nucleons in terms of phase-space cumulants [3] and found that the effect of cumulants cancels in the yield ratio up to the second order, which also includes the effect of radial expansions.
In the first part of this talk, we further investigate the effect of non-trivial phase-space distributions [3] by example distributions including the Woods-Saxon distribution, two Gaussian forms, and the blast-wave-type anisotropic flows. We find that the spatial structure decreases the ratio while the momentum anisotropy increases it. In the second part, we extend our analysis by evaluating the critical effect in the generalized light-nuclei ratio $N_p^{B-A}N_B^{A-1}/N_A^{B-1}$ [4,5] with $N_A$ being the nuclei yield of mass number A. We introduce the critical correction to the phase-space distribution by employing the critical fluctuations from the Ising model. We find that the overall non-monotonic behavior of the yield ratio arises from the increasing correlation length near the critical point. In addition, if the strength of the critical fluctuation is sufficiently significant, the collision energy dependence of the ratio exhibits double peaks by the interplay between the two- and three-point critical corrections.
[1] STAR Collaboration, arXiv:2209.08058 (2022).
[2] K.J.Sun, L.W.Chen, C.M.Ko and Z.Xu, Phys. Lett. B 774, 103-107.
[3] S. Wu, K. Murase, S. Tang and H. Song, Phys. Rev. C 106, 034905 (2022).
[4] S. Wu, K. Murase and H. Song, PoS (LHCP2022) 240.
[5] S. Wu, K. Murase, S. Zhao and H. Song, in preparation.
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 $\langle F_{\mu\nu}(x_{\alpha}) F_{\kappa\lambda}(y_{\beta}) \rangle$ 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, and softens the dependence on the IR-regulator by properly enforcing global color neutrality. The new model allows for a straight forward calculation of the time dependence of the gluon energy momentum tensor in early nuclear collisions in the weak field limit. We also discuss the initial motion of the nuclei after the collision and the momentum broadening coefficient at early times.
Isobar collisions, $^{96}_{44}$Ru+$^{96}_{44}$Ru and $^{96}_{40}$Zr+$^{96}_{40}$Zr, at $\sqrt{s_{\mathrm {NN}}}$ = 200 GeV have been performed at RHIC. These collisions are considered to be an effective way to minimize the flow-driven background contribution to search for the possibly small CME signal. Anisotropic flow is an important tool to understand properties of the QGP medium. Elliptic flow ($v_{2}$) is the second-order coefficient in the Fourier expansion of the azimuthal angle distribution of produced particles with respect to the reaction plane. Elliptic flow of charged hadrons has been measured in the isobar collisions at $\sqrt{s_{\mathrm {NN}}}$ = 200 GeV. The magnitude of $v_{2}$ shows difference between the two isobar collisions despite the same nucleon number. This indicates a difference in nuclear structure and deformation between these nuclei. The $v_{2}$ measurements of the strange and multi-strange hadrons are excellent probes for understanding these initial state anisotropies of the medium produced in these collisions, owing to their smaller hadronic cross-section compared to light hadrons. The collected datasets include approximately two billion events per isobaric species, offering a unique opportunity for making this statistically hungry measurement.
In this poster, we will report measurements of the elliptic flow of $K_{s}^{0}$, $\Lambda$, $\overline{\Lambda}$, $\phi$, $\Xi^{-}$, $\overline{\Xi}^{+}$, and $\Omega^{-}$+ $\overline{\Omega}^{\
+}$ at mid-rapidity for Ru+Ru and Zr+Zr collisions at $\sqrt{s_{\mathrm {NN}}}$ = 200 GeV. The transverse momentum ($p_{T}$) dependence of $v_{2}$ for minimum bias collisions and various centrality intervals will be shown. The $p_{T}$-integrated $v_{2}$ of these strange and multi-strange hadrons will also be shown. System size dependence of $v_{2}$ will be investigated by comparing the results in isobar collisions with those from Cu+Cu, Au+Au, and U+U collisions. The number of constituent quark (NCQ) scaling for these strange hadrons will also be tested. Experimental data will be compared with transport model calculations to provide insight into the nuclear structure of the isobars.
Two-particle correlation functions provide critical information about the medium quark--gluon plasma (QGP) created in heavy-ion collisions. Recent ALICE measurements have demonstrated large dynamical correlations between produced neutral and charged kaons in Pb--Pb collisions at $\sqrt{s_{\rm{NN}}} = 2.76 $ TeV~\cite{ALICE:2021fpb}. These integrated correlations cannot be described by conventional heavy-ion models, such as EPOS and AMPT. So far, the ALICE measurements can only be described by invoking the presence of condensates ~\cite{Kapusta:2022ovq}. A candidate for such a condensate is the Disoriented Chiral Condensate (DCC)~\cite{Mohanty:2005mv}. DCC arises from chiral symmetry restoration in the QGP, which breaks during the phase transition to form a condensate which coherently emits hadrons. Therefore, the discovery of DCC would indicate that chiral symmetry is restored in the QGP, a major prediction of QGP formation that has yet to be confirmed experimentally.
To investigate these anomalous kaon correlations further, a differential analysis of two-particle angular correlation functions of charged and neutral kaons as a function of $\Delta \varphi$ and $\Delta \eta$ in Pb--Pb collisions at $\sqrt{s_{\rm{NN}}} = 5.02 $ TeV is intended. The variables, $\varphi$ and $\eta$ are azimuthal angle and pseudorapidity respectively. The results from a simulation study using HIJING model, as a guide to the future exploration using heavy in data will be presented.
Multiple evidence reveals that the vast majority of the matter content of the universe is non baryonic and electrically neutral. This component is usually called Dark Matter (DM), for its lack of electromagnetic interactions, and is measured to constitute about 25% of the energy density of the Universe. The most common hypothesis is that it consists of weakly interacting massive particles, supposed to be cold thermal relics of the Big-Bang.
The indirect detection of DM is based on the search of the products of DM annihilation or decay. They should appear as distortions in the gamma ray spectra or in anomalies in the rare Cosmic Ray (CR) components. In particular, antimatter components, like antiprotons, antideuterons and positrons, promise to provide sensitivity to DM annihilation on top of the standard astrophysical production.
The interpretation of galactic CR data requires the correct modeling of their source terms and the turbulence spectrum of the galactic magnetic field, in addition to the knowledge of the cross sections that regulate the production of CR interacting with the interstellar medium.
After PAMELA detector results, the antiprotons flux has been measured with an accuracy of a few percent by AMS-02 over an energy range from below 1 GeV up to a few hundreds of GeV. However, the only currently measured production cross section is the proton-proton one, while all the reactions involving helium have no laboratory data in the phase space covered by AMS-02 (only LHCb, but with incident proton energy of 6.5 TeV). This requires a scaling of the pp channel to pA interaction through approximation and modeling.
The AMBER fixed target experiment at the M2 beam line at CERN will contribute to this fundamental DM search, performing a unique and complementary measurement of the double differential antiprotons production cross-section with a proton beam ranging from 60 to 250 GeV/c impinging on a liquid He target.
The data taking for the experimental determination of the cross-section in p+4He scattering is scheduled for May-June 2023. This result from AMBER will directly pin down the production of anti-protons in the relevant kinematical region covered by AMS-02.
The long-range ($|\Delta\eta| \gt 2$) near-side ($\Delta\phi\approx0$) ridge structure in a two-particle correlation analysis has been observed in heavy ion collision, which was well-explained by the hydrodynamic models based on the quark-gluon plasma (QGP) effect. However, even though small systems such as pp and pPb collisions cannot have enough density and temperature to create the QGP matter, the ridge phenomenon appeared in high multiplicity events of small systems, which is controversial in the hydrodynamic models. Among numerous models to explain this phenomenon in small systems, the Momentum Kick Model (MKM) can give a description of it via a kinematic process where the high-momentum jet particles transfer their momentum to the medium partons called a ``kick" process, leading to collective motion which becomes the ridge phenomenon in the MKM. The MKM has been applied to various experimental data, such as the STAR and the PHENIX, and has shown good agreement. Furthermore, since the ridge yields are dependent on multiplicity in high-energy collision experiments, C. Y. Wong built a multiplicity dependence on the MKM through an impact parameter and applied it to the CMS data for pp collisions at $\sqrt{s}=7$ TeV.
Recently, the CMS Collaboration measured the ridge yields along the different $p_T$ and multiplicity ranges for pp collisions at $\sqrt{s}=13$ TeV. To verify the MKM with multiplicity dependence, we expand the model analysis at 7 TeV to those at 13 TeV and provide the theoretical basis on two questions raised by the CMS Collaboration; the linearity of the ridge yield with multiplicity and the prominence at the middle $p_T$ range. Moreover, the CMS Collaboration suggested that the ridge structure does not have the collision energy dependence for pp collisions by comparing the ridge yields at 7 TeV with those at 13 TeV. From this surmise, we predict the future ridge behavior of the LHC Run3 at $\sqrt{s}=5.3$ and $8.5$ TeV.
Heavy-flavor (charm and beauty) quarks are generated primarily via hard scattering processes in high-energy hadronic collisions, and then undergo parton shower (fragmentation) and hadronization. Two-particle azimuthal correlations of heavy-flavor particles is a differential measurement which allows for the study of the fragmentation of heavy quarks. By measuring the azimuthal correlation in different transverse momentum ($p_T$) regions, one can study the details of the structure and particle momentum distribution of jets produced by the heavy-quark fragmentation process. The azimuthal correlations between electrons from heavy-flavor decays (trigger) and charged particles (associated) are studied in different trigger and associate particle $p_T$ regions. A distinguishing feature of heavy-ion collisions is the production of a hot and deconfined state of nuclear matter, called Quark Gluon Plasma (QGP). By comparing the heavy-flavor and charged particle azimuthal correlations in Pb-Pb collisions to measurements in smaller collision systems, we can determine how the heavy-quark fragmentation is modified by interactions with the QGP medium. In this poster, ALICE results on the modifications of the azimuthal distribution in Pb-Pb collisions with respect to pp collisions will be presented. The results in pp and p-Pb collision systems will also be shown and compared to predictions from Monte Carlo simulations.
The beauty quark is a unique probe to study the properties of quark-gluon plasma thanks to its large mass and relatively long thermal relaxation time compared with lighter partons. Traditional experimental observables such as elliptic flow v$_2$ and nuclear modification factor R$_{AA}$ of fully reconstructed beauty hadrons have been measured at the LHC. Moreover, indirect measurements on non-prompt D-mesons and heavy flavor decayed leptons have been carried out extensively. The sPHENIX experiment at RHIC is a state-of-the-art heavy flavor and jet detector. sPHENIX will begin commissioning with Au+Au collisions in Spring 2023. The Monolithic-Active-Pixel-Sensor (MAPS) based VerTeX detector (MVTX) is a high precision silicon pixel detector. The MVTX provides excellent position resolution and capability of operating in continuous streaming readout mode, allowing precise vertex determination and recording a large data sample, both of which are particularly crucial for b-hadron measurements. In this poster, we will discuss projections of inclusive b-hadron v$_2$ and R$_{AA}$ measurements and discuss the expected constraints on theoretical models. We will also report on the status of b-physics analysis.
Beauty quarks are produced in hard-parton scatterings in the early stages of the partonic collisions. They are the ideal probe to investigate the properties of Quark-Gluon Plasma (QGP) produced in ultra-relativistic heavy-ion collisions as they experience the whole QGP evolution. Due to their large mass, their production can be calculated using perturbative Quantum Chromodynamics (pQCD), thus they can be used to test pQCD based models. Moreover, measurements in p+p collisions provide the necessary reference for the interpretation of heavy-ion collision results. Experimentally, tagging a jet by its flavor content gives direct access to the initial parton kinematics and can provide information on how the energy is dissipated in the QGP medium. The possible studies include the flavor and mass dependence of jet quenching, the collisional energy loss, the dead-cone effect, and the modification of the fragmentation and jet structure in the medium.
The sPHENIX detector will begin commissioning with Au + Au collisions in Spring 2023. It provides an excellent vertex resolution using 3 layers of Monolithic Active Pixel Sensors (MAPS) and Intermediate Silicon Tracker (INTT) detectors. The expected spatial resolution is <6μm and the track vertex distance of closest approach (DCA) <30 $\mu$m for p$_T$>1 GeV/c. In addition, a full azimuthal coverage of electromagnetic and hadronic calorimeters provides an excellent tool to study jet physics. In this poster, we will focus on the prospects of beauty-jet-tagging of full jets at sPHENIX. Several methods are studied in simulation, including tagging via the large DCA track and secondary vertex mass.
In ultra-relativistic heavy-ion collisions, the colliding nuclei are decelerated and kinetic energy is converted into new particles. This energy loss is referred to as baryon stopping. A fundamental question one can ask in the study of high energy heavy-ion collisions is how much baryon stopping there is. This can be quantified by measuring the net proton rapidity distributions. Previous measurements at RHIC and in fixed target experiments have shown that the amount of stopping decreases with increasing collision energy. At LHC energies, there are no experimental constraints beyond the central rapidity region, where there are no net protons.
In order to investigate the net proton distribution at LHC energies beyond mid-rapidity, we propose using the bremsstrahlung photons emitted from the nuclei as they slow down. In our recent study [1], we investigated stopping scenarios which are based on model calculations or phenomenology and consistent with existing data. Furthermore, we performed a detailed estimate of the background from hadronically produced photons, using the PYTHIA 8.3 event generator, aiming to investigate in which areas of phase space the bremsstrahlung photons constitute a viable observable for baryon stopping. The bremsstrahlung spectra are highly sensitive to the amount of nuclear stopping, and depending on the scenario, a significant signal over background is obtained for pseudorapidities η>∼4−5 and for photon energies ω<∼300−500MeV.
Here, we expand our investigation to include the baryon stopping predicted by the EPOS4 event generator for PbPb collisions at sqrt(sNN)=5.02TeV. EPOS4 gives zero net protons at mid-rapidity, making the bremsstrahlung spectrum from this stopping scenario plausible.
Furthermore, we discuss the bremsstrahlung spectrum coming from proton-proton collisions, which gives insight into the charge dependence of the signal to background ratio of bremsstrahlung photons in hadron collisions.
[1] S. Nese and J. Nystrand, Eur. Phys. J. C 83 (2013) 14. arXiv:2210.16200.
Fluctuations of conserved quantities are proposed as a powerful observable to search for the QCD critical point. Recently, proton cumulants from central Au+Au $\sqrt{s_{NN}}$ = 3 GeV collisions were reported, which implies that hadronic interactions are dominant at 3 GeV and the QCD critical point could exist at the collision energies higher than 3 GeV. The baryon-strangeness correlation is expected to deviate from the QGP expectation for the hadronic gas at high baryon-chemical potential region, which can be used to confirm the turning-off signal of the QGP. Previously, the STAR measurement of baryon-strangeness correlation using (anti)protons and $\rm K^{\pm}$ shows no strong signal compared with theoretical prediction. So it is suggested to include hyperons in the measurement to study QCD phase transition.
In this poster, we will report the second-order baryon-strangeness correlation using proton, $\rm K^{\pm}$, and $\Lambda$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 3 GeV from the fixed-target program at the STAR experiment. Protons and $\rm K^{\pm}$ are identified using TPC and TOF detectors, while $\Lambda$ is reconstructed by the invariant mass method. Physics implications of the results, as well as comparisons with model calculations, will be discussed.
The sPHENIX TPC readout will use an array of quadruple-stacked gas electron multiplier (GEM) modules to amplify signals from the chamber in order to perform precise tracking measurements. The performance of the system may be affected by a shift in the readout baseline due to event-by-event fluctuations. These fluctuations are a result of the common-mode noise generated in the induction gap of the readout as well as the ion tails on the signals caused by capacitive coupling between the bottom GEM and pad plane of each module. Understanding and accounting for this baseline shift is necessary to avoid degradation in the tracking performance of the TPC. We will present studies done to investigate the baseline shift of the sPHENIX TPC readout along with the methods used to correct for it.
Ultra-relativistic heavy-ion collisions at RHIC are thought to have created a Quark-Gluon-Plasma (QGP) with a very low shear viscosity in the deconfined phase. However, as the QGP hadronizes it will evolve through a hadronic phase with rapidly increasing shear viscosity. In order to fully characterize the QGP state, one has to separately determine the viscosity of the hadronic phase. Although many approaches have been used to determine the shear viscosity coefficient and the associated shear viscosity to entropy density ratio ($\frac{\eta}{s}$) in the hadronic phase, much is unknown regarding the bulk viscosity to shear viscosity coefficient ($\frac{\zeta}{s})$ in the hadronic phase. We present preliminary results of a calculation of the bulk viscosity $\zeta$ and the bulk viscosity to entropy density ratio $\frac{\zeta}{s}$ for hot hadronic matter. The Ultrarelativistic Quantum Molecular Dynamics (UrQMD) model is used to simulate the hadronic medium and periodic boundary conditions are used to simulate infinite hot equilibriated hadronic matter. The Green-Kubo formalism is employed and a comparison is made with the results of the bulk viscosity calculation from the Simulating Many Accelerated Strongly Interacting Hadrons (SMASH) model from [1].
[1] J.B Rose et al 2021 J. Phys. G: Nucl. Part. Phys. 48 015005
The sPHENIX detector at Brookhaven National Laboratory’s (BNL) Relativistic Heavy Ion Collider (RHIC) is scheduled to begin data acquisition in 2023. Its primary objective is to investigate the microscopic properties of the Quark-Gluon Plasma (QGP) through high-precision measurements of jets and heavy flavor observables. A key feature of the sPHENIX detector is the inclusion of hadronic calorimeters (HCals) at mid-rapidity, which are essential for the jet physics program. Accurate jet reconstruction demands properly calibrated sPHENIX calorimeter systems during the entire data collection process. This study aims to build on previous cosmic testing efforts, which were conducted using individual HCal sectors in test benches, by investigating the potential for cosmic calibration with the complete sPHENIX apparatus in its data-taking position. In this poster, we will present a GEANT4-based study that employs a cosmic muon generator with a realistic zenith angle and energy distribution to examine the possibility of calibrating the HCals to the Minimum Ionizing Particle (MIP) scale using cosmic muon events. The muon rate predictions and observations will be utilized to plan routine cosmic running, ensuring the maintenance of the calibration for the lifetime of the sPHENIX experiment.
With the advent of the Electron Ion Collider, which will involve many diverse calorimeter systems, and the switch to SiPM readouts which has been occuring over the past ~decade, new techniques in calorimeter calibrations are needed. These should address for example, gain tracing vs time, where siPM's can be more sensitive to temperature fluctuations, and also position dependencies in response, due to siPM light collection being less uniform than with traditional PMT's. We review several calibrations methods used for calibrating both hadronic and electromagnetic calorimeters at RHIC, LHC, and elsewhere, and also explore some possibilities for use at the upcoming EIC Facility. This includes several novel techniques developed for use at RHIC by our group. We will discuss calorimeter systems being planned for the ePIC experiment and specifically how the various methods, including ours, can be used there.
Electromagnetic probes have been established as promising tools to study early times in the collision system of maximum temperature and density.
In this contribution, a focus is set on the investigation of collective observables. Namely, the directed flow $v_1$, elliptic flow $v_2$ as well as the radial flow of virtual photons are measured. After the isolation of the thermal contribution, a systematic study as a function of the invariant mass may allow unique insights into the time evolution of the systems collectivity.
The analysis is based on Ag+Ag collisions collected at the High-Acceptance-DiElectron-Spectrometer (HADES) at $\sqrt{s_{NN}}=2.55$ GeV and $\sqrt{s_{NN}}=2.42$ GeV. Therefore, the created matter is characterised by high baryon densities and moderate temperatures, similar to neutron star mergers, and serves as an important reference to deliver constraints to the equation of state.
High-energy heavy-ion collisions offer a unique and precise way to probe nuclear structures by providing a snapshot of the nuclear distribution at the time of the collision, which is complementary to low-energy nuclear physics experiments.
In this talk, we present a comprehensive scan of flow observables, including anisotropic flow coefficients, nonlinear flow modes, and normalized symmetric cumulants, in Pb--Pb and Xe--Xe collisions measured with ALICE at $\sqrt{s_\mathrm{NN}} =$ 5.02 and 5.44 TeV, respectively. These measurements can probe distinctive nuclear structures (i.e., quadrupole deformation) in central collisions and the size of the $^{208}$Pb neutron skin in midcentral to peripheral collisions. The measurements of multiparticle cumulants of mean transverse momentum, $[p_\mathrm{T}]$, allow us to probe the size and its fluctuations in the initial state. Furthermore, we present the first measurements of newly proposed multiparticle cumulants between anisotropic flow $v_{\rm n}^{\rm m}$ (m = 2,4) and mean transverse momentum correlations $[p_\mathrm{T}^{(k)}]$ (k $\leq$ 4), in both Pb--Pb and Xe--Xe collisions. The presented measurements and comparisons to the state-of-the-art theoretical model calculations show unambiguous evidence of a deformed and triaxial structure for $^{129}$Xe, and in Pb--Pb collisions further provide tight constraints to the nucleon width $w$, which was poorly controlled before. These studies enormously improve our understanding of the initial conditions of heavy-ion collisions and allow us to explore LHC's full potential as a robust nuclear physics machine.
The sPHENIX Time Projection Chamber (TPC) is a gaseous drift detector
designed to measure charged particle tracks. It is filled with Argon/CF4 and uses
Gaseous Electron Multiplier (GEM) foils at readout for electron amplification
and ion back-flow suppression. The electrons at readout are measured, converted
to digital current, and their signal waveforms are processed to reconstruct the track.
At this stage, the positions of hits and clusters along the track can be measured.
A successful measurement of these hits and clusters must correct for
distortion effects present in the TPC. There are three primary sources of distortion: static
distortions from E and B fields, average distortion from space charge, and event-by-event distortions due to fluctuations in space charge. This poster focuses on
a novel technique to measure the static distortions using a system of steerable
ionizing lasers. These provide straight tracks at many different angles with
an ability to sample the entire TPC volume between periods when beam is
present. These laser induced tracks are used measure the distortions from non-uniform
and slightly misaligned drift electric fields and solenoidal magnet fields in single
voxels of the TPC. From these measurements, one can determine the static
distortion correction. This poster presents the methodology by which the TPC
volume is sampled by steering the laser and how the distortions are measured
from reconstructed laser data.
The Time Projection Chamber (TPC) is the main tracking detector in sPHENIX. Charged particles which pass through the TPC ionize the gas, with the transverse position being given by the readout pad and the time for the ionization electrons to drift to the endcaps defining the z position. The ionization electrons are clustered together in order to track particles and determine their momenta. In order to accurately track particles, calibrations must be performed and the performance of the TPC must be understood. As part of normal operation, space charge builds up within the TPC, leading to tracking distortions. These distortions must be accurately characterized over time such that they can be corrected as they evolve. Several calibration systems are used for this, including a set of diffuse lasers which illuminate the Central Membrane of the TPC. Aluminum stripes, deposited on the Central Membrane at well-surveyed positions, emit photoelectrons when struck by the diffuse laser. The resulting pattern can be reconstructed and used to characterize the 3-dimensional distortions at the position of the Central Membrane. These distortions are then extrapolated to the endcaps of the TPC in order to provide corrections throughout its entire volume. This poster will discuss the design, the algorithm, and the performance of the time dependent distortion corrections in the sPHENIX TPC and identify how this effort fits into the broader sPHENIX TPC calibration scheme.
The sPHENIX Time Projection Chamber (TPC) serves as the main tracking detector of the sPHENIX experiment, which began operating at the Relativistic Heavy Ion Collider at Brookhaven National Lab this year. It operates with a quadruple-GEM avalanche stage which provides gain while restricting the flow of ions back into the chamber sufficiently to operate in streaming mode, without any additional gating. However, in order to reach its design performance, the time-varying distortions due to the fields of the remaining ion backflow and primary ionization must be monitored and corrected. The slowly varying component of the distortions is monitored by the TPC Outer Tracker (TPOT), a micromegas-based detector which provides an additional spacepoint for tracks within a limited azimuthal range. This spacepoint enables a data-driven extraction of the distortion vectors within the detector, which can then be extrapolated to the entire chamber. This poster presents the design of the TPOT and methods used to extract the appropriate corrections to these moderate-timescale distortions
The RHIC Beam Energy Scan (BES) program aims to study the properties of strongly interacting matter in relativistic heavy-ion collisions at various energy densities and temperatures. Correlation femtoscopy technique is a useful tool to study systems undergoing QCD phase transitions, and can extract valuable information about the size, shape, and lifetime of the particle-emitting source in heavy-ion collisions.
This study presents the first comprehensive femtoscopic analysis of identical kaons and pions produced in Au+Au collisions at $\sqrt{s_{NN}}$ = 14.6 - 200 GeV from the RHIC Beam Energy Scan phases I and II, focusing on charge, transverse momentum, and centrality-dependent properties. The charge-dependent analysis reveals differences at the level of correlation functions for both kaons and pions for the first time at these energies. This observation is consistent with Coulomb field effect due to residual charge after the collision and hadronic final state effects, as implemented in UrQMD. The three-dimensional femtoscopic analysis reveals that the extracted radii, assuming Gaussian distribution for emission source, increase with collision energy, decrease with transverse mass, and are generally larger for kaons compared to pions under the same conditions. The study compares experimental data with different model scenarios and discusses the implications of the trend of the extracted size and lifetime of the particle source with the change of collision energy.
An analysis of one-dimensional two-pion and two-kaon correlations in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV, utilizing Levy-stable distributions for the source shapes, is also presented. The current analysis status of the extracted Levy source parameters, including their dependence on average transverse mass and centrality, is reported. A comparison of the pion and kaon Levy exponent is presented, potentially shedding light on the deviation from the Gaussian approximation of the emission source. The obtained results are compared to UrQMD and EPOS model calculations.
The multiplicity distribution measures the probability of obtaining a certain number of particles in a given collision and is one of the first observables measured in data at each new collision type and center of mass energy. It is relevant since is one of the fundamental observables to describe the global properties of the interactions and is sensitive to non-linear QCD evolution in the initial state. We will present the multiplicity distribution, P(N_\mathrm{ch}), for Pb-Pb collisions at \sqrt{s_\mathrm{NN}} = 5.36 TeV. The analysis relies on tracks reconstructed with ALICE's upgraded Inner Tracking System (ITS) using new LHC data from Run3 pilot Pb-Pb run. A detailed comparison with predictions from the PYTHIA 8 and EPOS LHC event generators is also presented.
Multiplicity distributions of primary charged particles are sensitive to non-linear QCD evolution in the initial state. We present the distributions in various pseudorapidity ranges in proton-proton collisions at $\sqrt{s}$ = 13.6 TeV. Charged particles are reconstructed using the Inner Tracking System that has been upgraded for Run3 at LHC and is operation starting in 2022. The data are compared to models with recent PYTHIA 8, EPOS-LHC, and EPOS 3.
sPHENIX, the first detector to be built at the Relativistic Heavy-Ion Collider (RHIC) in over two decades, will bring unprecedented measurement capabilities at RHIC energies. One of the initial physics measurements to be performed by sPHENIX concerns the charged-particle multiplicity, which utilizes the tracklet analysis method with the cluster information from the Monolithic-Active-Pixel-Sensor-based Vertex detector (MVTX). This measurement serves to directly demonstrate, based on real collision data, that the MVTX readout and clustering are operational. Additionally, this analysis technique provides an alternative diagnostic tool for detector alignment and vertex finding, both of which are critical components of the tracking system that will enable the entire physics program of sPHENIX. The projected performance of the measurement will be presented, and the status of the analysis on 2023 Au+Au data will be discussed.
We study the production of charm quarks in hot QCD medium described by quasiparticle excitations of quarks and gluons. The effective masses are adjusted through the coupling to satisfy the entropy density obtained on the lattice [1]. The evolution of the QGP is described by hydrodynamic simulations in (2+1) dimensions with temperature-dependent shear viscosity taken into account [1,2]. The temperature and time evolution of the charm quark number obtained in the above-described scenario is further juxtaposed to the results acquired from ideal QGP obeying Bjorken flow. We observe a suppression of charm quark production in the absence of shear viscosity and transverse expansion [3]. Moreover, we compute the charm quark fugacity by solving the rate equation and find that it exhibits a global attracting solution, specific to the differential equations [4].
[1] V. Mykhaylova, M. Bluhm, C. Sasaki, K. Redlich, Phys.Rev.D 100 (2019).
[2] J.Auvinen, K. J. Eskola, P. Huovinen, H. Niemi, H.Paatelainen, Phys.Rev.C 102 (2020).
[3] V. Mykhaylova, Transport Properties of Hot QCD Matter in the Quasiparticle Approach (PhD Thesis, 2023).
[4] V. Mykhaylova, EPJ Web Conf. 274 (2022) 05006.
Quarkonium production is considered one of the golden probes of the quark-gluon plasma (QGP) formation in heavy-ion collisions.
Due to their large mass, the production of heavy-quarks is governed by hard scales of QCD, while the formation of the bound quarkonium state involves soft QCD scales.
The regeneration process of J/$\psi$ in the QGP or at the phase boundary is crucial for describing the observed centrality, rapidity, and $p_{\mathrm T}$ dependence of J/$\psi$ nuclear modification factor at the LHC.
Quarkonium production in more dilute systems is essential to provide a baseline for Pb--Pb results.
They are also useful for investigating the production mechanisms for pp collisions and studying the cold nuclear matter effect for p--Pb collisions.
The $\psi$(2S) production relative to J/$\psi$ is observable with strong discriminating power between the two regeneration scenarios in Pb--Pb collisions, as well as among quarkonium production models in pp and p--Pb systems.
Thanks to the ALICE online single-electron triggers from the Transition Radiation Detector (TRD), the $\psi$(2S) signal can be extracted at midrapidity in the dielectron channel.
In this contribution, the first studies on J/$\psi$ and $\psi$(2S) productions at midrapidity with the TRD-triggered data measured in ALICE in pp collisions at $\sqrt{s} = 13$ TeV will be shown for the first time, along with recently published J/$\psi$ results based on TRD-triggered data in p--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 8.16$ TeV.
The AdS/CFT correspondence, which connects strongly coupled conformal field theories in $N$ dimensions to gravity in $N+1$ dimensional Anti-de Sitter space, has provided valuable insights into the non-perturbative aspects of QCD. Soft-wall AdS/QCD is a phenomenological model that uses a dilaton field to introduce confinement, while a scalar field is dual to the chiral condensate. The thermodynamics of the deconfined state are introduced using an asymptotically AdS Reissner-Nordström black hole, which includes both temperature and baryon chemical potential. Minimal models of this type yield a chiral phase transition that is not affected by the chemical potential, and thus lack a critical point.
In this work, we investigate the chiral phase transition in an AdS/QCD action that includes a coupling between the scalar and dilaton fields. Our results reveal that the scalar-dilaton coupling produces a rich phase structure, with the emergence of a critical point at finite temperature and density. The location and presence of the critical point is found to be highly sensitive to the strength of the scalar-dilaton coupling. We present results for both 3-flavor symmetric and 2+1 flavor cases. This work provides a foundation for future phenomenological applications, as well as dynamical models, which solve the scalar and dilaton fields using the gravitational equations of motion.
Balance functions have been extensively used to elucidate the time evolution of quark production in heavy-ion collisions. Early models predicted two stages in the quark production, one for light quarks and one for the slightly heavier strange quark, separated by a period of isentropic expansion. This led to the notion of clocking the particle production and tracking radial flow effects. The evolution of the azimuthal widths of the Balance functions has been later associated to the diffusivity of light quarks.
In this contribution, Balance functions in different multiplicity classes of pp Run 3 collisions at $\sqrt{s} = 13.6\;\text{TeV}$ recorded by ALICE are reported and compared with ALICE published results on pp collisions at $\sqrt{s} = 7\;\text{TeV}$. Results not only allow to validate the new data-taking machinery and analysis framework but also shed light on the evolution of Balance functions, their widths, and integral, with the collision energy. with the collision energy.
The Time Projection Chamber (TPC) at sPHENIX provides particle tracking over pseudorapidity $|\eta| <$ 1.1, and plays a key role in the planned jet and heavy-flavor measurements. The electrons created through ionization of the TPC gas by charged particles produce hits on the TPC readout plane, from which clusters for track reconstruction need to be formed. The traditional method of grouping connected hits into clusters, known as connected component analysis (CCA), becomes less effective in high-multiplicity events, such as Au+Au collisions with event pileup from multiple beam crossings, due to effects from $\delta$-electrons and the high occupancy. A neural network (NN) clustering method, which uses an NN to predict the cluster position based on the distribution of hits, is supposed to improve the clustering performance. We simulate high-multiplicity events and the sPHENIX detector response and train the NN to predict the associated truth cluster position based on the distribution of the reconstructed hits. We will show the implementation of NN clustering at sPHENIX and our plans to enhance its performance by improving truth-information association and fine-tuning the parameters of the NN.
We study charmonium states, J/ψ, ψ(2S), and χc1(1P) mesons in heavy ion collisions by focusing on their production from charm and anti-charm quarks in a quark-gluon plasma by coalescence. Starting from the investigation on the difference in their internal structures, or different wave functions of charmonium states we calculate the yield and transverse momentum distributions of charmonium states produced in heavy ion collisions. We show that the wave function distribution plays a significant role, especially, in the production of charmonium states, leading to the transverse momentum distribution of the ψ(2S) meson as large as that of the J/ψ meson. We also discuss the anisotropic flow, or elliptic and triangular flow of charmonium states using the transverse momentum distribution of charmonium states. We find that the internal structure differences as well as feed-down contributions of charmonium states are averaged out for elliptic and triangular flow, resulting in similar elliptic and triangular flow for all charmonium states. Based on our evaluation of elliptic and triangular flow of charmonium states we also discuss the quark number scaling of elliptic and triangular flow for charmonium states in heavy ion collisions.
Many physics observables of interest in heavy-ion collisions require knowledge of the collision geometry. Geometric fluctuations lead to different symmetry planes of the initial geometry for each harmonic number, called participant planes. As the produced medium evolves, pressure gradients transform the initial state spatial anisotropy into final state momentum anisotropy. The angular distribution of particles can be described via Fourier coefficients $v_n$. The participant planes can be approximated via event planes, $\psi_n$, which are determined from measured azimuthal distribution of particles produced in the collision. This poster reports the methods used for event plane determination in sPHENIX as well as the performance using a variety of sPHENIX subsystems based on simulation using a realistic GEANT description of the experiment. Initial results from the first data run will also be discussed..
We present a relativistic density functional approach to color superconducting quark matter that mimics quark confinement by a fast growth of the quasiparticle self-energy in the confining region [1]. The approach is shown to be equivalent to a chiral model of quark matter with medium dependent couplings. The approach to the conformal limit at asymptotically high densities is provided by a medium dependence of the vector-isoscalar, vector-isovector and diquark couplings motivated by non-perturbative gluon exchange [2]. While the (pseudo)scalar, vector-isoscalar and vector-isovector sectors of the model are fitted to the mesonic mass spectrum and vacuum phenomenology of QCD, the strength of interaction in the diquark channel is varied in order to obtain the best agreement with the observational constraints from measurements of mass, radius and tidal deformability of neutron stars. These constraints favor an early onset of deconfinement and color superconductivity in neutron stars with masses below one solar mass. We also discuss a new two-zone interpolation scheme for the construction of the hadron-to-quark matter transition [3] that allows to test different structures of the QCD phase diagram with one, two or no critical endpoints in simulations of supernova explosions, neutron star mergers and heavy-ion collisions. We argue that the formation of color-superconducting quark matter drives the trajectories of its evolution in supernovae and neutron star mergers towards the regimes reached in terrestrial experiments with relativistic heavy ion collisions.
[1] O. Ivanytskyi and D. Blaschke, Phys. Rev. D 105, 114042 (2022)
[2] O. Ivanytskyi and D. Blaschke, Particles 5, 514 (2022)
[3] O. Ivanytskyi and D. Blaschke, Eur. Phys. J A. 58, 152 (2022)
The new sPHENIX detector at RHIC will begin commissioning with Au+Au collisions at 200 GeV in Spring 2023, followed by p+p and p+Au data taking in 2024. The experiment combines triggered readout of the calorimeter system with streaming readout of the tracking detectors in a hybrid readout scheme. The hybrid readout scheme enables a large increase in the collected statistics in particular for p+p and p+Pb collisions at RHIC, leading to an enhancement in integrated luminosity for low p$_T$ heavy-flavor measurements by more than two orders of magnitude.
We will present an overview of the detectors and their readout, the design and functioning of the DAQ system, and its performance. We will explain how sPHENIX has implemented the streaming readout, which is the planned readout mode for future experiments like, e.g., ePIC, for the participating detector systems. The operational and performance experience in the first data taking run will be discussed, and the event statistics collected for key physics channels will be presented.
Net-charge, net-strangeness and net-baryon number fluctuations measured in ultra-relativistic heavy-ion collisions may reveal details and insights into the quark-hadron transition, hadro-chemical freeze-out and possibly aid in the search of the QCD critical point. By controlling the collision energy, some current and upcoming heavy-ion facilities aim to study high energy nucleus-nucleus collisions in the finite net-baryon density regime where the effects of rapid global rotation are also expected to be strong for the peripheral collisions. We discuss the ratios of conserved number susceptibilities that are experimentally measurable via products of the moments of the corresponding distributions and compute the relevant theoretical results in the framework of a rotating hadron resonance gas (rHRG) model.
Constructed at Lehigh University between 2021 and 2023, the sPHENIX Event Plane Detector (sEPD) will measure charged particle multiplicity at forward rapidity from the collision of hadrons. This detector consists of 24 triangular sectors, each of which is divided into 31 optically isolated tiles of plastic scintillating material, such that light can be collected from a discrete area of the detector then converted later to an electronic signal. A wavelength shifting fiber is glued into each tile using an optical epoxy with an index of refraction matching that of the scintillator. The tiles cover 16 segments in $\eta$ and 24 in $\phi$. The sectors were installed into two disks covering a pseudorapidity of 2.1 < |$\eta$| < 4.9. To build the detector, scintillating plastic was milled into a triangular shape to create 24 sectors. Grooves for the optical fibers were then machined into the sectors, in addition to channels to divide each sector into 31 tiles. Optical fibers were then glued into the grooves, and the channels were filled with a reflective epoxy to achieve optical isolation between tiles. An overview of this construction process will be given in detail, including the machining of the sectors, the installation of the fibers in the tiles, and the creation of two types of bundles of fiber optic assemblies.
This material is based upon work supported by the National Science Foundation under Grant No. 2117773.
HADES has a large acceptance as well as excellent particle identification capabilities and therefore allows the study of dielectron, hadron, and light nuclei production in heavy-ion collisions with great precision. The harmonic flow coefficients $v_n$ of the order $n = 1 − 6$ are measured with HADES as a function of centrality, transverse momentum, and rapidity in Au+Au collisions at 1.23 AGeV. Combining them allows to construct for the first time a complete, multi-differential picture of the emission pattern as a function of rapidity and transverse momentum.
The predictions of ideal hydrodynamic simulations, confirmed by transport model calculations, suggest a scaling between various flow coefficients. For protons at mid-rapidity the ratio $v_{4}/(v_{2})^{2}$ is found to be close to 0.5. The correlations of flow coefficients are investigated based on an event-by-event selection of the mid-rapidity final state elliptic flow of protons. The correlations are compared to the results of transport models and to eccentricity calculations within the Glauber Monte Carlo approach.
This work is supported by the Helmholtz Forschungsakademie HFHF.
Correlations involving the seven conserved quantities, $\{E,\vec{p},Q,S,B\}$, were modeled for heay-ion collisions at finite baryon density. The evolution of correlations as a function of relative rapidity was treated as a linear response to local thermodynamic fluctuations of on the Bjorken-model background. The entire 7x7 matrix of correlations was found to be significant, sensetive to the EoS, viscosity and diffusivity. Oportunities for experimental observation will be presented.
Correlations between net-conserved quantities such as net-baryon, net-charge and net-strangeness are essential probes of QCD phase structure and are related to the ratios of thermodynamic susceptibilities in lattice QCD calculations. The study of these correlations can probe thermal conditions in a medium and help to elucidate the nature of the strongly interacting matter formed in high-energy nuclear collisions. Recent lattice QCD results suggest that the presence of a magnetic field has a significant impact on the ratios of thermodynamic susceptibilities. Therefore, correlations between net-conserved charges could be used to study the magnetic field produced in peripheral heavy-ion collisions.
We present the new results on the first-order correlations of net-proton, net-charge, and net-kaon, where net-proton and net net-koan act as a proxy of net-baryon and net-strangeness, respectively. The measurements are performed as a function of centrality in Pb--Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV using the data recorded by the ALICE detector. The results are compared with corresponding results at lower collision energies from the STAR experiment at RHIC and with theoretical predictions from lattice QCD, the Hadron Resonance Gas model, and the HIJING event generator.
We present energy loss predictions of B and D-mesons at $\sqrt{s}=200$ GeV in pA collision systems. We assume that the medium produced in these collisions is strongly coupled, and show the centrality and momentum dependence of the nuclear modification factor at midrapidity. We also quantify the systematic theoretical uncertainties in these predictions that are a result of the mapping of parameters in $\mathcal{N}=4$ SYM theory to QCD, as well as the momentum dependence of the diffusion coefficient in AdS/CFT. We then present results of the corresponding $v_2(p_T)$ for B and D-mesons describing this azimuthal anisotropy for central, semi-central and peripheral collisions.
In this work, we investigate the color-spin interaction of a quark, a diquark and a baryon with their surrounding baryons and/or quark matter. This is accomplished by classifying all possible flavor and spin states of the resulting multiquark configuration in both the flavor SU(2) and SU(3) symmetric cases. We also discuss the three-body confinement potential and show that this does not contribute to the outcome. Furthermore, we find that a quark becomes more stable than a baryon when the number of surrounding baryons is three or more. Finally, when we consider the internal color-spin factor of a probe, our results show that the effects of the color-spin interaction of a multiquark configuration is consistent with the so-called diquarkyonic configuration.
Studies of charm production in proton-proton ($pp$) collisions are essential to understand some of the most fundamental aspects of Quantum Chromodynamics. They also provide the baseline for interpretation of charm data from larger colliding systems. Over the last decade, the measurement of the production cross-sections of charm mesons and baryons in $pp$ collisions has been at the centre of a wide experimental effort at the Large Hadron Collider (LHC). These cross-sections were measured over a wide transverse momentum and rapidity coverage, thanks to the complementary kinematic acceptance of the different LHC experiments. In this study, the measurements of the charm hadrons $D^0$, $D^+$, $D_s^+$, $\Lambda_c^+$ and $\Xi_c^0$ performed by the ALICE, CMS and LHCb collaborations in $pp$ collisions at the centre-of-mass energy $\sqrt{s}=\rm 5.02$ TeV are combined in transverse momentum and rapidity, and, using the most recent theoretical calculations, are extrapolated to the full phase space to determine the total charm-quark production cross section $\sigma_{c\bar{c}}$. We will discuss the final result, which increases the existing tension between experimental data and fixed order calculations, together with comparisons to PYTHIA predictions.
The quark-gluon plasma (QGP) is a liquid created in high-energy heavy-ion collisions where quarks and gluons become deconfined. This state allows us to examine the emergent properties of quantum chromodynamics (QCD) under extreme conditions. sPHENIX, a new experiment at RHIC, studies the QGP created in Au-Au collisions and started taking data in 2023. Collimated sprays of particles, called jets, may be created in these collisions, typically in back-to-back (dijet) configurations. These dijets are produced prior to the formation of the QGP and interact with it during their development, losing energy ins a process called “jet quenching” which probes the nature of the QGP. When these dijets do not pass through the same path-length of QGP, the energy loss will be asymmetric. The dijet momentum imbalance (x$_J$) is defined as the ratio between the sub-leading (second highest energy) jet’s energy and the leading (highest energy) jet’s energy, and is a useful measure of energy loss. However, dijet measurements are sensitive to the underlying event and detector resolution. To correct for these effects we examine the development and application of Bayesian unfolding techniques on PYTHIA jets embedded into HIJING Au+Au background. Future uses will include implementation on measured dijet distributions in sPHENIX.
In this poster, PHENIX presents a proof of principle study for the measurement of prompt and non-prompt $e^{+}e^{-}$ pair production in the intermediate mass range ($m_{\phi}$ $<$ $m_{ee}$ $<$ $m_{J/\psi}$) using $p$+$p$ data at 200 GeV taken in 2015. PHENIX plans to extend the measurement to the high statistics Au+Au data-set recorded in 2014 and 2016, with the goal to isolate the expected prompt thermal contribution in the intermediate mass region from non-prompt pairs from heavy flavor decays. In $p$+$p$ collisions the main physics signal in this mass region originates from semileptonic decays of charm and bottom $q\bar{q}$ pairs. The $e^+$ and $e^-$ origin from decays many micron away from the interaction point. This non-prompt component is identified statistically by measuring the distance of closest approach (DCA) with the PHENIX silicon vertex detector (VTX). The VTX has four layers with a total radiation length of about 15\%, thus electrons from photon conversions cause a significant combinatorial background for the measurement, even in $p$+$p$ collisions. We have developed rejection techniques that effectively eliminate this background, improving the signal-to-background ratio by orders of magnitude. We will present the $e^{+}e^{-}$ pair spectra from $p$+$p$ collisions and its non-prompt contributions.
Results from heavy-ion collisions confirmed the scenario in which the deconfined state of nuclear matter, dubbed the quark--gluon plasma (QGP), undergoes a collective expansion. Collective anisotropic flow, quantified with Fourier harmonics of azimuthal distribution of particles, $v_n$, is one of the most sensitive experimental probes to constrain QGP properties. Recently developed multi-harmonic flow observables, Symmetric Cumulants (SC) and Asymmetric Cumulants (AC) of $v_n$ amplitudes, provide new and independent information from their correlations and fluctuations, since they satisfy all fundamental properties of multivariate cumulants in a strict mathematical sense.
In this contribution, the first differential measurements of SC and AC observables in Pb--Pb collisions measured with ALICE as a function of kinematic variables are presented. The analysis is performed in parallel using the legacy code and the newly deployed O2 framework for Run 3 analyses in ALICE.
We present the first results for dielectron anisotropic flow computed directly from hadronic transport in different systems, and explore the different calculation methods. Because leptons are insensitive to the strong interaction, they are mostly undisturbed by the hadronic medium created after a heavy-ion collision, and therefore serve as direct probes for it. In particular, the HADES experiment at GSI measures flow of dielectrons using the reaction plane method, which can lead to large systematic uncertainties. At the low beam energies of GSI, the evolution is mainly off-equilibrium, and hadronic transport provides an appropriate description and gives access to the full phase space, as well as knowledge on the dilepton origin, being a useful tool in studying the mechanisms behind flow generation from this off-equilibrium hadron resonance gas.
In this contribution we present results on the dielectron production in $Ag+Ag$ collisions (0-40% centrality) and $p+p$ interactions at $1.58 \, AGeV$ beam energy measured with the High Acceptance DiElectron Spectrometer (HADES). The HADES RICH detector has been upgraded with a new photon detection camera which strongly enhances the electron efficiency and conversion pair rejection. With this upgrade, a signal-to-background ratio of about 1 is achieved in the dielectron spectrum around $500 \, MeV/c^2$, even in $Ag+Ag$ collisions. $5\,$billion $Ag+Ag$ collisions have been analyzed showing a signal up to the $\phi$ meson mass region. A clear excess of dileptons is seen above the contributions from initial state processes and late meson decays which serves as messenger of the dense medium created in heavy-ion collisions. This excess reveals the thermal properties and the lifetime of the medium but also gives insight into meson properties at high densities.
To disentangle the various contributions to the measured dielectron yield it is important to precisely understand the dielectron production in elementary reactions. Therefore, HADES has recently measured $0.5\,$billion $p+p$ collisions at the same energy, where preliminary results will be presented in addition. These serve as baseline for the understanding and interpretation of the $Ag+Ag$ data.
The anisotropic flow parameters $(v_{n})$ offer insights into collective hydrodynamic expansion and transport properties of the produced medium at higher collision energies, while they are sensitive to the compressibility of the nuclear matter and nuclear equation of state at lower collision energies. Among them directed flow ($v_1$) describes the collective sideward motion of produced particles in heavy-ion collisions. It is an important probe to study the in-medium dynamics as it is sensitive to the equation of state (EoS) of the produced medium. Minimum in the slope of directed flow ($dv_1/dy$) as a function of collision energy has been proposed as a signature of the first-order phase transition between hadronic matter and quark-gluon plasma. The triangular flow $(v_3)$ typically arises from the initial condition fluctuations and is expected to be uncorrelated to the reaction plane. However, recent measurements at lower collision energies show a correlation between $v_3$ and the first-order event plane angle ($\Psi_{1}$).
In this poster, we will report measurements of $v_1$ and $v_3$ for $\pi$, $K$, $p$, $d$, and $t$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 3.2, 3.5, 3.9, 4.5, 6.2, 7.2, and 7.7 GeV in fixed-target mode from the second phase of beam energy scan (BES-II) program at RHIC-STAR. The rapidity, centrality, and collision energy dependence of $v_1$ and $v_3$ will be shown and their physics implications will be discussed.
Studying hyper-nuclei production and their collectivity can shed light on their production mechanism as well as the hyperon-nucleon interactions under finite pressure. This is a unique opportunity for heavy-ion collisions at high baryon density region where hypernuclei production rate increases.
In this poster, we will present $v_{1}$ of the hyper-nuclei ($\Lambda$, $^{3}_{\Lambda}{\rm H}$, $^{4}_{\Lambda}{\rm H}$) from mid-central Au+Au collisions at $\sqrt{s_{NN}}$ = 3.2, 3.5, and 3.9 GeV, collected by the STAR experiment with the fixed-target mode during the second phase of the RHIC beam energy scan program. The rapidity dependence of the hyper-nuclei directed flow ($v_{1}$) is studied in mid-central collisions. The extracted $v_{1}$ slopes of the hyper-nuclei are positive and decrease gradually as the collision energy increases. The results will be compared with models using the framework of hadronic transport and a coalescence after-burner.
With the extreme temperatures and energy densities generated by ultra-relativistic heavy-ion collisions, a new state of matter with surprising fluid properties will be created. Non-central heavy-ion collisions can generate a large initial angular momentum, resulting a strong vortical of $\omega \approx (9 \pm 1)× 10^{-21} s^{−1}$ in the fluid, estimated from the global $\Lambda$ hyperon polarization measurements in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. This vortical structure may change the azimuthal distribution of the particle produced in the fluid.
We study the directed flow ($v_{1}$) of charm hadrons and light flavor hadrons in relativistic heavy-ion collisions based on a multiphase transport model (AMPT) framework with an initial vortical pattern in the partonic interaction phase. We find that the $dv_{1}/dy$ as a function of rapidity for pion and kaon are reversed compared to the default AMPT setting and are comparable to the measured value at RHIC energy. And the $dv_{1}/dy$ slope of $D^0$ meson increased by more than 2 times with the vorticity and also compared to the $D^0$ $v_{1}$ measurements from RHIC.
Directed flow of particles is an important feature seen in heavy-ion collisions and is a sensitive probe to the equation of state (EoS) of the matter produced in the collisions. Model calculations have also predicted that directed flow could be sensitive to the softening of EoS associated with a first order phase transition. Directed flow of protons and anti-protons are also of interest as they offer sensitivity to both the contributions from the transported quarks and the component generated by medium interactions at the later stage. Measurements of proton and net proton directed flow from BES-I have shown that there is a non-monotonous dependence on collision energy.
In this poster, We will present measurements of the directed flow of protons and antiprotons from 19.6, 14.5, 11.5, 9.2, and 7.7 GeV Au+Au collisions, using high statistics BES-II data from STAR. We will also present a decomposition of proton directed flow into a medium interaction generated component and a component (v1excess) attributed to transported protons. The v1excess component is found to show a simple scaling between collision energies of 200 GeV to ~10 GeV, but to break the scaling at energies below that. The new results have significantly reduced uncertainties and also allow differential measurements in centrality and transverse momentum. Results will be compared to different model calculations and implications to the understanding of the QCD phase structure and EoS of the medium will be discussed.
The Time Projection Chamber (TPC) to be used for tracking and particle identification in the sPHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) is expected to experience significant distortions from build-up of backflowing ions created by the combination of high collision rates and amplification from Gas Electron Multiplier (GEM). By integrating the digitized readout from the detector, one produces a 'digital current' which serves as a proxy for the ion backflow current. The digital current can then be used to reconstruct the ion space charge density to calculate the electric and magnetic field distortions in the chamber, but at significant computational cost. Machine learning methods provide a mechanism to reduce this computational cost while also reducing errors by training and validating with experimental data. We will present methods and results using machine learning techniques to predict and correct for space-charge induced distortions in the sPHENIX TPC.
The nuclear modification factor related to the Drell-Yan (DY) production cross-section is an excellent probe of the cold nuclear matter (CNM) properties. The acceptance of the sPHENIX detector allows detection of DY events in the dielectron channel for p$_\perp$ ≳ M, where p$_\perp$ is the dilepton transverse momentum and M its invariant mass. In this kinematic region, the DY cross-section is dominated by NLO gluon Compton scattering allowing access to the gluon density of the nucleus, xG(x). The DY events extraction requires a precise knowledge of the QCD background contributing to the dilepton invariant mass spectrum. A fit to the latter one is carried out including opencharm (OC), open-bottom (OB), charmonium ($\psi$) and bottomonium ($\Upsilon$) simulations. The CNM effects are investigated via the rapidity and p$_\perp$ distributions of the DY lepton pair, and the possible impact of sPHENIX DY data on the xG(x) extraction is discussed. In addition, energy loss and broadening calculations based on Landau-Pomeranchuk-Migdal (LPM) model are shown.
In the chiral limit the complicated many-body dynamics around the second-order chiral phase transition of two-flavour QCD can be understood by appealing to universality. We present a novel formulation of real-time functional renormalization group that describes the stochastic hydrodynamic equations of motion for systems in the same dynamic universality class, which correspond to Model G in the Halperin-Hohenberg classification, and preserves all the relevant symmetries of such systems with reversible mode couplings. We show that the calculations indeed produce the non-trivial value z=d/2 for the dynamic critical exponent, where d is the number of spatial dimensions. We also extract the critical momentum dependence of the charge diffusion coefficient. We keep the degrees of freedom of the order parameters general and show that for N=3 we recover standard Model G dynamics and for N=2 we recover Model E dynamics.
We analyze the effect of hydrodynamic fluctuations on normalized mixed harmonic cumulants ($nMHC$) [1,2] for the first time based on event-by-event simulations of high-energy heavy-ion collisions using an integrated model of an initial state model, stochastic causal fluctuating hydrodynamics, and a hadronic afterburner.
For the quantitative constraints on the transport properties of quark-gluon plasma (QGP) and the initial-state models, it is important to compare various flow correlations from dynamical models to data. Recently, $nMHC$ was shown to be useful in constraining theoretical models [3]. Meanwhile, we have shown that hydrodynamic fluctuations affect the longitudinal factorization ratio $r_n(\eta_a,\eta_b)$ [4] and can reproduce the experimental centrality dependence with initial longitudinal fluctuations [5]. However, it is non-trivial how the hydrodynamic fluctuations affect the constraints on the QGP properties through various flows and correlations.
In this talk, we investigate the effect of hydrodynamic fluctuations on $nMHC$ in $\sqrt{s_\mathrm{NN}}$=2.76 TeV Pb+Pb collisions. We combine the $\mathtt{TRENTo}$ initial conditions and the $\mathtt{UrQMD}$ afterburner used in Refs. [3,6] with relativistic fluctuating hydrodynamics $\mathtt{rfh}$ [6]. We first compare the results with and without hydrodynamic fluctuations and see the effect. We next consider different temperature dependencies of viscosity. We find that the hydrodynamic fluctuations tend to decrease $nMHC$, which is because they de-correlate initial correlations. In particular, $nMHC(v_2^2,v_3^2)$ is sensitive to the hydrodynamic fluctuations but almost insensitive to the viscosity. We also discuss the effect of the rapidity gap. We argue that $nMHC$ is useful for identifying the effect of hydrodynamic fluctuations and is a key to properly constraining the theoretical models.
[1] Zuzana Moravcova, Kristjan Gulbrandsen, You Zhou, Phys. Rev. C 103, 024913 (2021).
[2] S. Acharya et al. (ALICE), Phys. Lett. B 818, 136354 (2021).
[3] M. Li, Y. Zhou, W. Zhao, B. Fu, Y. Mou, and H. Song, Phys. Rev. C 104, 024903 (2021).
[4] Azumi Sakai, Koichi Murase, Tetsufumi Hirano, Phys. Rev. C 102, 064903 (2020).
[5] Azumi Sakai, Koichi Murase, Tetsufumi Hirano, Phys. Lett. B 829, 137053 (2022).
[6] Kazuhisa Okamoto and Chiho Nonaka, Phys. Rev. C 98, no.5, 054906 (2018).
[7] Koichi Murase, Ph. D. thesis (University of Tokyo), (2015).
In heavy ion collisions, the initial state geometry plays a crucial role in determining final state observables such as elliptic flow $v_2$ and radial flow reflected by event-wise average transverse momentum $[p_{\rm T}]$. The initial state geometry is influenced by several nuclear shape parameters, including quadrupole deformation (β), triaxiality (γ) [1], nuclear radius (r), and skin depth (a) [2]. It is known from low-energy physics that many atomic nuclei exhibit a quadrupole shape that fluctuates around an average profile. This talk investigates the impact of nuclear shape fluctuations on initial state geometry in heavy ion collisions, focusing on eccentricity ($\epsilon_2$) and inverse transverse size ($d_⊥$), which are linearly related to fluctuations of flow, i.e. $v_2 \propto \epsilon_2$ and $\delta [p_T]\propto \delta d_{\perp}$, and comparing them across different system sizes. Our aim is to quantify the effects of these parameters on initial state observables in a coherent manner. We show that overall quadrupole deformation fluctuations enhance the cumulants of $\epsilon_2$ and $d_⊥$, while triaxiality fluctuations reduce the differences between prolate and oblate nuclei. Our results suggest that, in the large fluctuation limit, the initial state observables' values approach those obtained in collisions of rigid triaxial nuclei.
[1] Impact of nuclear shape fluctuations in high-energy heavy ion collisions
[2] Scaling approach to nuclear structure in high-energy heavy-ion collisions
The effect of the hadronic phase on jet quenching in nuclear collisions is largely an open question, although there are tantalizing hints from previous studies that the effects might be sizable. We have implemented a hadronic afterburner phase for jet fragmentation hadrons in the JETSCAPE framework using SMASH. We have applied the new setup to $e^++e^-$, $p+p$ and $A+A$ systems in order to study the effects of hadronic rescattering. For a quantitative analysis we compare simulations, with and without rescatterings of shower hadrons during the afterburner phase. We report here effects on hadron spectra and jet observables as a function of collision system, collision energy and multiplicity.
The Quark Gluon Plasma (QGP) produced in relativistic heavy ion collisions exhibits a nearly perfect fluid behavior. This behavior is observed as strong azimuthal correlations between the produced particles. Measurement of $J/\psi$ azimuthal correlations can provide key information about the charm quark dynamics in the QGP. Strong elliptic flow of $J/\psi$ has been observed in Pb+Pb collisions at the LHC and attributed to $J/\psi$ production through coalescence of charm quarks that flow with the medium. At RHIC, the $J/\psi$ flow measurements at mid-rapidity are presently inconclusive, while measurements of the nuclear modification factors at mid- and forward rapidity hint that coalescence may play a role in central collisions. The PHENIX experiment at RHIC has a unique coverage at forward rapidity $(1.2\leq|\eta|\leq2.2)$ and a large sample of $J/\psi\rightarrow\mu^++\mu^-$ decays collected in 2014 in Au+Au collisions at 200 GeV. We will present a statistically improved measurement of $J/\psi$ elliptic flow at RHIC at forward rapidity.
To incorporate the effect of gluons on the evolution dynamics of the quark matter produced in relativistic heavy-ion collisions, we extend the three-flavor Nambu–Jona-Lasinio (NJL) transport model to include the contribution from the Polyakov loops. Imbedding the resulting pNJL partonic transport model in an extended multiphase transport (extended AMPT) model, we then study the elliptic flow splittings between particles and their antiparticles in relativistic heavy-ion collisions at beam energy scan energies. We find that a weak quark vector interaction in the partonic phase is able to describe the elliptic flow splitting between protons and antiprotons in heavy-ion collisions at √sNN = 7.7 to 39 GeV. Knowledge of the quark vector interaction is useful for understanding the equation of state of quark matter at large baryon chemical potentials and thus the location of the critical point in the QCD phase diagram.
Nuclear modification factors ($R_{AA}$) of leading particles provide valuable information about the flavor dependent magnitude and characteristics of parton energy loss in $A+A$ collisions. Experimental measurements of $R_{AA}$ exhibit a distinct different dependence on transverse momentum ($p_{T}$) at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). Previous analyses of RHIC data treated the difference in the $p_{T}$ spectrum between $p+p$ and $A+A$ collisions as a leading parton $p_{T}$ loss and empirically concluded that the flat $p_{T}$ dependence of $R_{AA}$ corresponds to a constant fractional $p_{T}$ loss ($\Delta p_{T}/p_{T}$) [1]. This feature of $\Delta p_{T}$ proportional to $p_{T}$ can be understood via elastic collisions in classical dynamics. We analyze LHC measurements of the strong $p_{T}$ dependence of $R_{AA}$ for light and heavy flavor leading particles. Our analyses indicate that LHC data for a variety of leading particle species are consistent with $\Delta p_{T}$ proportional to $\sqrt{p_{T}}$, in contrast to proportional to $p_{T}$ at RHIC. In addition, Charm hadrons exhibit differing behavior compared to the other species studied, revealing possible unique heavy flavor dynamics. These distinct features are consistent with the scenario of increased contributions from radiative energy loss at LHC energies compared with stronger collisional energy loss dominance at RHIC energies. Moreover, linear trends between fractional energy loss and initial parton density at varying $p_{T}$ magnitudes indicate that the amount of parton energy loss does not depend strongly on the traversing geometrical path length of the parton during collision evolutions, which is in agreement with previous empirical findings at RHIC despite significant different initial parton densities formed at LHC and RHIC. We will also discuss further implications of the observed proportionality in LHC data and differences in fractional energy loss at varying $p_{T}$ scales.
[1] Wang, G. and Huang, H. Phys. Lett. B 672, 30 (2009).
Measurements of heavy quarkonia in heavy-ion collisions play a crucial role in studying the properties of the quark-gluon plasma (QGP). The dissociation of J/$\psi$, caused by the color screening effect, was proposed as a direct signature of the QGP formation. However, recombination of deconfined charm-anticharm (c$\bar{c}$) pairs complicates the interpretation of the observed J/$\psi$ suppression in heavy-ion collisions, and its contribution is expected to be smaller at lower collision energies. Therefore, measuring the beam energy dependence of J/$\psi$ production will help disentangle different effects.
In this poster, we report the measurements of inclusive J/$\psi$ production in Au+Au collisions at $\sqrt{\mathrm{s_{NN}}}$ = 14.6, 19.6 and 27 GeV using the Beam Energy Scan Phase II (BES-II) data recorded by the STAR experiment. The J/$\psi$ invariant yields and nuclear modification factors ($R_{AA}$) are presented as a function of centrality and transverse momentum. Beam energy dependence of J/$\psi$ $R_{AA}$ is discussed together with model comparisons.
Jets are excellent probes for studying the deconfined matter formed in heavy ion collisions. However, competing energy-loss effects, such as the dependence on the opening angle of the shower, radiative emissions to large angles, and the medium response to the jet, can obscure interpretation. This talk presents two new observables aimed at disentangling these effects. First, we introduce a new infrared and collinear safe measurement of the jet energy flow within jets reconstructed with different resolution parameters $R$. Changing the jet $R$ varies the relative contribution of competing energy-loss effects. Additionally, we utilize the excellent ALICE PID capabilities in new measurements of jet-hadron correlations with identified hadrons and identified hadron ratios in jets in pp and Pb-Pb collisions at $\sqrt{s_{\rm{NN}}} = 5.02~\mathrm{TeV}$. The final state jet hadrochemical composition can differ from the vacuum due to medium-induced modifications to jet fragmentation or the medium response. Finally, the ALICE PID capabilities can also be exploited to study gluon jet fragmentation with the new LHC data in pp collisions at $\sqrt{s} = 13.6~\mathrm{TeV}$.
Chiral media, such as quark-gluon plasma, possess a number of unique properties originating from the quantum phenomenon of the chiral anomaly. These properties can be measured by observing the propagation of fast charged particles moving through the medium and the radiation produced in the process. We show how the chiral anomaly confers distinctive features onto the particle energy loss and its radiation spectrum. We argue then that this makes quantum tomography a powerful and versatile tool to investigate the properties of chiral systems ranging from the Weyl semimetals to the quark-gluon plasma to the axion stars.
Based on Hansen and Tuchin, Phys. Rev. C 104, no.3, 034903 (2021) and Phys. Rev. D 105, no.11, 116008 (2022).
Energy-energy correlators (EEC) offer a novel way to study the structure of jets. Defined as the energy-weighted cross section of particle pairs inside jets, the correlation strength as a function of the pair opening angle allows a distinct separation of the perturbative and non-perturbative regimes. The evolution of parton dynamics in jets to their confinement into hadrons can be studied. Measurements of jets initiated by heavy quarks play an important role in the testing of pQCD calculations and represent a critical component of the studies of quark-gluon plasma (QGP) created in heavy-ion collisions. We present the first measurements of the EECs for D$^0$-tagged jets in pp collisions at 13 TeV with the ALICE experiment at the LHC. By comparing our results with EEC’s in inclusive (gluon-dominated) jets, we can search for modifications in the radiation pattern of jets due to mass effects such as the dead cone. We also compare with perturbative QCD predictions to measure the onset of non-perturbative physics. These measurements will also serve as a baseline for future studies in heavy-ion collisions, allowing for disentanglement of the dynamics of the dead cone from interactions with the quark-gluon plasma.
Energy-energy correlators (EEC) have been proposed to study the structure of energy flow within jets. These functions are defined as the energy-weighted cross-section of particle pairs inside jets. The correlation as a function of pair distance and jet transverse momentum offers a clear separation between the perturbative and non-perturbative regimes, where one can probe the dynamics of quarks and gluons and their confinement into hadrons. In this work, using data from the ALICE experiment, we present measurements of 2-point EECs in p-Pb collisions at 5.02 TeV. By comparing these results to a p-p baseline, we can study the changes to jet dynamics caused by interactions between color charges and a cold nuclear medium. In particular, we can look into how the presence of cold nuclear matter modifies the hadronization mechanism.
In an effort to better understand the thermal-like behavior and particle yields seen in p-p collisions we recast the problem employing the principles of quantum states and their entanglement in the produced system. We seek to show that this entanglement in the initial state has a measurable effect on the evolution of the system and is the driving mechanism behind the thermal-like behavior and particle yields observed. Recent studies have demonstrated that entanglement in the initial state could endure the evolution of a strongly coupled system. Consequently, we attempt to show equivalence in a calculation of the initial state entropy (calculated using PDF’s) and the final state entropy (calculated using multiplicity distributions). Multiplicity distributions used in this study are that of primary charged particles, measured using the ALICE detector at the LHC.
Multiplicity data on $\rm\bar{p}$p/pp collisions at {\footnotesize SPS} and {\footnotesize LHC} energies (0.2-7 TeV) are used to study the entropy production, dimensions and other multifractal characteristics of multiplicity distributions of relativistic charged particles produced. It is observed that the entropy produced in smaller and(or) larger phase space bins, when normalized to maximum rapidity, exhibits a kind of scaling which is nicely supported by Monte Calro model, {\footnotesize PYTHIA-8} with color-reconnection({\footnotesize CR}) switched-$`$on'. Using the Renyi's order-q information entropy, multifractal characterisitcs of multiplicity distributions are studied in terms of generalized dimensions, $\rm D_q$. Nearly the same value of multifractal specific heat, $`$c' $\sim 0.1$, are observed which agrees fairly well with those reported earlier for hadron-hadron (hh) collsions at lower energies. These findings, therefore, suggest that the parameter $`$c' may be taken as the universal characterisitc of multiparticle production in hh collisions. {\footnotesize PYTHIA} model, however, predicts somewhat lower values of $`$c' as compared to those obtained with the data. The analysis is further extended to examine the spectrum of scaling indices, which might lead to make some useful conclusions on the energy dependence of degree of multifractality and smoothness of the rapidity distributions.
Measurements of azimuthal correlations of charmed mesons in high-energy heavy-ion collisions can shed light on the transport properties of the Qaurk-Gluon Plasma. The STAR experiment at the Relativistic Heavy Ion Collider (RHIC) collected in 2014 and 2016 a large sample of Au+Au reactions at $\sqrt{s_{NN}}$ = 200 GeV making such a study possible. The sPHENIX experiment will also offer a similar opportunity in the next few years. However, such a measurement in $p$+$p$ collisions at the same energy has not been feasible so far.
To provide a baseline for the heavy-ion measurements, we report studies of the azimuthal correlations between charmed mesons in $p$+$p$ reactions using two Monte Carlo event generators, PYTHIA 8 and Herwig++. We validate the models against the available data from the STAR and CDF experiments, and compare their predictions to deliver a reliable $p$+$p$ baseline for heavy-ion collision studies. Finally, we discuss prospects for performing such measurements in $p$+$p$ collisions at RHIC.
The initial state of heavy-ion collisions has a short lifetime and cannot be directly measured. As a result, various initial condition models exist. Although averaged event observables with different initial condition models give comparable results, event by event analysis can help to identify systematic differences. To determine the initial conditions is crucial to assess systematic uncertainties of Bayesian analysis, that aim at the extraction of transport coefficients from experimental data. The qualitative impact of the choice of initial conditions in hydrodynamical simulations is studied on an event-by-event basis in the hybrid approach SMASH-vHLLE-Hybrid\textsuperscript{1}, composed of the hadronic transport approach SMASH\textsuperscript{2} and the (3+1)d viscous hydrodynamic code vHLLE\textsuperscript{3,4}. Event-by-event correlations are studied for SMASH IC as well as for IP-Glasma and TRENTO, with and without early time out-of-equilibrium dynamics, for Au-Au collisions at $\sqrt{s_{NN}}=200$ GeV in different centrality classes.
We observe that the initial state eccentricities $\epsilon_2$ and $\epsilon_3$ are, depending on the setup and the model, not independent and show correlations which also result due to the assumed linear response of flow to eccentricity\textsuperscript{5} in correlations between the elliptic and triangular flow. Additionally, we also study initial momentum space information present in the SMASH and IP-Glasma initial condition models. We find that for very spherical events, the initial state momentum anisotropy significantly contributes to the final state momentum anisotropy, which means that the description of such events is especially sensitive to the choice of the initial state model.
References:
[1] https://github.com/smash-transport/smash-vhlle-hybrid
[2] https://github.com/smash-transport/smash
[3] https://github.com/yukarpenko/vhlle
[4] I. Karpenko, P. Huovinen, M. Bleicher, Comput. Phys. Commun. 185 (2014).
[5] J. Noronha-Hostler et al., Phys. Rev. C 93.1 (2016).
A hot and dense system formed in heavy-ion collisions can be characterized by studying the scaling behavior of the spatial distributions of the produced particles. In this contribution, we present intermittency analysis of the normalized factorial moments ($F\rm{_{q}}$) of the multiplicity distributions of the charged particles produced in Pb--Pb collisions as a function of phase-space resolution. The spatial configurations of the charged particles in two-dimensional ($\eta,\varphi$) phase space are investigated. For a system with scale-invariant dynamical fluctuations due to the characteristic critical behavior near the phase transition, the $F\rm{_{q}}$ exhibits power-law growth with increasing phase-space resolution, which is a signature of self-similar fluctuations and the fractal structure of the system. The dependence of the fractal dimension $D_{q}$ on the order parameter $q$ is indicative of the multifractal nature of the system. By relating the $q^{\rm{th}}$-order $F\rm{_{q}}$ to the normalized second-order factorial moment ($F\rm{_{2}}$), we extract the scaling exponent ($\nu$), which provides information about the order of the phase transition in the framework of the Ginzburg-Landau theory. The first results of the intermittency analysis show the presence of scale-invariant fluctuations, the multifractal nature of the system, and that $\nu$ is independent of $p\rm{_{T}}$ in the soft $p\rm{_{T}}$ region. The measurements are also compared with the corresponding results from the AMPT and HIJING models.
Partonic scatterings with high momentum transfer occur before the formation of the quark-gluon plasma (QGP) in heavy-ion collisions and result in collimated collections of hadrons, called jets. The modification of the high-virtuality parton shower in the QGP compared to that in proton-proton collisions offers insight into the nature of the medium's interactions with colored probes. To study the path-length dependence of hard partons traveling through the QGP, we apply a technique known as event-shape engineering to data from heavy-ion collisions at $\sqrt{s_{\mathrm{NN}}}=200\ \mathrm{GeV}$ at STAR. Within a given eccentricity and centrality class, charged hadrons traveling in the event plane direction (having shorter path length) are compared to those traveling perpendicular to it (having longer path length). By fixing the centrality, we can control for the energy density. We then report a comparison of the ratios of in-and out-of-plane charged hadron spectra between two eccentricity classes, which accesses the dependence of energy loss on the collision geometry.
Hadronic resonances are interesting candidates to study the properties of the hadronic phase, which is the time span between the chemical and kinetic freeze-outs, formed during the evolution of relativistic heavy-ion collisions. Due to their short lifetimes, comparable to the lifetime of hadronic phase ($\sim$10 $-$ 12 fm/$c$), they decay in the hadronic phase and their decay products undergo rescattering or regeneration within the hadronic gas. Thus, the yields of the hadronic resonances alter than what was originally produced before the chemical freeze-out. This change in their yield, which is extensively studied to understand the properties of the hadronic phase, depends upon the lifeime of the decaying resonance, the interaction cross-sections of its decay daughters, and the lifetime of the hadronic phase. \
In this study, we explore the production yields of hadronic resonances by simulating pp, p$-$Pb and Pb$-$Pb collisions at various centre of mass energies using the latest EPOS4 model. The EPOS4 model employs a comprehensive scheme for simulating high-energy particle collisions, which includes primary interactions based on S-Matrix theory, secondary interactions using a core-corona separation approach, hydrodynamic evolution, micro-canonical hadronization, and a final hadronic afterburner using UrQMD. This scheme allows for the simulation of parallel scatterings and accurately models the complex dynamics of high-energy particle collisions, thus providing some new understanding of a deep connection between four basic concepts in pp and AA collisions: parallel scattering, energy conservation, factorization, and saturation. We measure the transverse momentum spectra ( $p_{\rm{T}}$ ), energy dependence of resonance production, ratio of yield of resonance particles to their corresponding stable particles, nuclear modification factor ( $R_{\rm{pA}}$ and $R_{\rm{AA}}$) for various hadronic resonances of different lifetimes and compare the results with the data available from the ALICE experiment at CERN.
Exploring the transport coefficients of the QGP is one of the main goals in relativistic heavy ion collisions. By employing the Bayesian analysis method, the temperature dependent shear and bulk viscosity of QGP medium has been extracted. However, the heat conductivity of the QGP has not been fully explored. Using single-shoot MUSIC hydrodynamics with smooth initial condition, ref.[1] found that turning on the heat conductivity of the QGP tends to transport net baryon number towards mid-rapidity.
In this talk [2], we study the heat conductivity using event-by-event hydrodynamic simulations (iEBE-MUSIC) with the dynamical initial conditions. We will show that some of the three-particle flow correlations are sensitive to the heat conductivity of QGP, which can be used to constrain the heat conductivity at RHIC Beam Energy Scan.
[1]Gabriel S. Denicol, Charles Gale, Sangyong Jeon, Akihiko Monnai, Björn Schenke, and Chun Shen, Phys. Rev. C 98, 034916 (2018).
[2]Shujun Zhao, Chun Shen, Huichao Song, paper in preparation.
The investigation of light hadrons in UPCs is of great interest for QCD studies. ALICE is a superb detector for studying these processes because of its excellent particle identification and tracking capabilities. The measured cross section of coherent $\rho^{0}$ mesons in photon-lead interactions has been found to be about 40% smaller than what is predicted by the Glauber model, and expectations from photon-proton interactions, indicating the importance of high-mass intermediate states in the process of $\rho^{0}$ scattering off nuclei. In this talk, we will review the status of the coherent $\rho^{0}$ meson analysis, and present the first study of the photoproduction of the two-kaon final state channel in UPCs, which could originate from the decay of the $\phi$ meson or from direct production. ALICE can also study four-prong states which are interesting for spectroscopy and excited resonance searches. In this talk, we will discuss new results on exclusive four-pion states.
The Chiral Mean Field model (CMF) has been successful in describing the equation of state at large baryon densities, such as those found in neutron stars, neutron star mergers, and heavy-ion collisions. The MUSES collaboration has rewritten the zero-temperature CMF model from Fortran 77 into a parallelized modern C++20 using OpenMP, which has resulted in at least an order of magnitude improvement in runtime. We obtained equations of state across $\mu_B$, $\mu_S$, and $\mu_Q$, and within the metastable regime around the quark deconfinement phase transition. The improved numerical resolution allows for the accurate computation of higher-order derivatives such as susceptibilities. Finally, we computed neutron star observables like quadrupole moment, Love number, moment of inertia, and mass-radius curve.
Heavy-ion collisions produce a quark-gluon plasma that undergoes rapid expansion and cooling, which presents a challenge for calculating jet quenching observables. Current approaches rely on analytical results for static cases, introducing theoretical uncertainties and biases in our understanding of the pre-equilibrated medium. To address this issue, we employ analytical re-summation schemes to incorporate multiple scattering in a class of expanding backgrounds. By introducing a new length scale related to the equilibration time of the QGP, we investigate the range of validity of Bethe-Heitler emissions, LPM interference effects, and higher-twist contributions to the emitted gluon spectrum. We also discuss methods to mitigate the non-local nature of the emission spectrum. Our analysis shows that strong jet quenching is only possible when the equilibration time of the medium is longer than its mean free path, highlighting the importance of medium modifications of jets in the earliest stages of heavy-ion collisions. By accounting for the expansion of the medium, our approach reduces the uncertainties in model predictions for jet quenching observables, providing insights into the nature of the pre-equilibrated medium. This work lays the foundation for further investigations into the dynamics of the QGP and the interplay between jets and the expanding medium.
Studying atomic nuclei's deformation and substructure, including quadruple, triaxial, and octupole shapes, is crucial to understanding nuclear structure comprehensively. The cluster structures depend on variables such as excitation energy, core clusters, and excess neutrons. Although clusters are tightly bound in low-lying states, the correlation between clusters and their formation is not fully understood. Our ongoing feasibility studies, utilizing different energy and number correlations and momentum correlation function measures, show promising results. We used the proposed EPIC detector at the Electron-Ion Collider and the BeAGLE model to simulate collisions between e+Be, e+C, e+O, e+Pb, and e+U, which will be presented and discussed. Our findings indicate that using the EIC's mid- and forward-rapidity ePIC detectors could provide new insights into alpha clustering and nuclear deformation in atomic nuclei.
The thermal fluctuations in the QGP medium formed in heavy ion collisions present themselves as event-wise $[p_\mathrm{T}]$ fluctuations in the final state. Recent studies have shown that the average and higher-order fluctuations of $[p_\mathrm{T}]$ in ultra-central collisions are sensitive to radial flow, random thermal motion, and nuclear deformation, and can provide constraints on the extent of thermalization of the QGP droplet. This talk presents new precise measurements of $[p_\mathrm{T}]$ cumulants up to 3rd order in $^{129}$Xe+$^{129}$Xe and $^{208}$Pb+$^{208}$Pb collisions. The multiplicity dependence of $[p_\mathrm{T}]$ cumulants show deviations from expected power-law behavior. The average $\left\langle[p_\mathrm{T}]\right\rangle$ shows a non-trivial rise in the ultra-central collisions, whereas the variance shows a clear and sharp drop in ultra-central collisions. The skewness, expected to be more sensitive towards higher $p_\mathrm{T}$ particles, also shows a non-trivial increase in ultra-central collisions. All observables also show a clear dependence on the $p_\mathrm{T}$ ranges in consideration and the centrality estimator used in the analysis. These results have strong implications for understanding the impacts of the initial condition, medium thermalization, and medium properties on final state $[p_\mathrm{T}]$ fluctuations.
Recent measurements in proton-proton (pp) and proton-lead (p--Pb) collisions have shown features that are reminiscent of those observed in lead-lead (Pb--Pb) collisions, such as near-side long-range correlations, mass-dependent hardening of ${p}_{\mathrm T}$ spectra, strangeness enhancement etc. Therefore, one of the key challenges today is understanding the origin of strangeness enhancement in small collision systems at very high energies, i.e. the increase of (multi-)strange hadron yields relative to non-strange hadron yields with increasing charged-particle multiplicity ($\mathrm{d} N_{\mathrm{ch}}/\mathrm{d}\eta_{~\left | \eta \right |~<~0.5} ~<$ 100) and saturation for high multiplicities.
We report the new preliminary mid-rapidity measurement of the transverse momentum spectra and yields of ${\rm K^{0}_{s}}$, $\Lambda$ and $\bar \Lambda$ in the p--Pb collision system at $\sqrt{s_{\rm NN}}$ = 8.16 TeV. The ratio of baryon to meson yields and the nuclear modification factor will also be included. These observables are used to study the hadronization process in small collision systems. Results have been obtained in several multiplicity bins, so that a comparison to lower energy p--Pb results and to similar measurements in pp and Pb--Pb collisions can be performed. Finally, the comparison to phenomenological models including the latest version EPOS4 and Pythia8 will be discussed.
Exploring thermoelectric Figure of Merit in QCD medium with conserved charges
It is the goal of the RHIC BES program and the future FAIR, NICA facilities to produce baryon-rich matter. In these low-energy HIC experiments, diffusion processes of conserved charges play a vital role in dynamic evolution of dense QCD matter. Recently, thermoelectric effects such as Seebeck effect, which have been extensively studied in condensed matter materials, have also captured the attention of high-density HIC physics. Thermoelectric Figure of Merit (ZT), which reflect strong couplings among electrical conductivity, thermal conductivity, Seebeck coefficient and temperature, can be used as a common benchmark to quantify the effeciency of meterial at heat-to-electricity conversion.
We focus on the ZT in hadronic phase, where the themoelectric transports of mutiple conserved charges (the baryon number, strangeness and electric charge) are fully considered. The different transport coefficients matrices are estimated using the Boltzmann kinetic theory in Hardron Resonance Gas model with and without repulsive mean field effect. We also study the effect of magnetic field on ZT. Different to zero magnetic field, additional transverse ZT can appear at finite magnetic field, and we for the first time distinguish the calculation results of themoelectric coefficients in QCD medium under the adiabatic and isothermal condition. Finally, we establish the relations between ZT and $\sqrt{s_{NN}}$ to better exhibit the thermoelectric properties of QCD medium at different collision energies.
We investigate the characteristics of gluonic cascades in static and expanding media by numerically solving the complete BDIM (Blaizot-Dominguez-Iancu-Mehtar-Tani) evolution equations in longitudinal and transverse momentum using the Monte Carlo event generator MINCAS. In this analysis, we compare angular distributions of in-cone radiation across various medium profiles with effective scaling laws. Our findings indicate that the out-of-cone loss of energy occurs through the radiative break-up of hard fragments, which is followed by an angular broadening of soft fragments. Although the broadening of the leading fragments is substantially impacted by the dilution of the medium caused by expansion, we find that in the low-x range, which is accountable for the majority of gluon multiplicity in the cascade, the angular distributions are almost identical when comparing different medium profiles. This similarity is primarily because multiple splittings play a dominant role in broadening within this range. Lastly, we examine how our findings influence the phenomenological explanation of jet quenching and out-of-cone radiation.
It is well established that the late states of a high energy nuclear collision can be described in terms of relativistic fluid dynamics. An open problem in this context is how the actual collision and the early time dynamics directly after it can be described. Phenomenological models are currently employed here and they have several parameters that need to be fitted to experimental data.
Using relativistic fluid dynamics of second order we develop a new approach which addresses the entire collision event, and which gets initialized in fact already before the collision. This is based on the droplet model for the incoming nuclei and a state-the-art equation of state including the first-order liquid-gas phase transition. The physics picture we propose assumes that the soft features of a high energy nuclear collision can be fully described through the dynamics of the energy-momentum tensor and other conserved currents.
This work is part of and supported by the DFG Collaborative Research Centre "SFB 1225 (ISOQUANT)".
The Electron Ion Collider offers unprecedented opportunities to image the proton and nuclei. The Far Forward detectors serve to classify the nature of the electron-proton or electron-nucleus interaction by identifying forward proton, neutrons and photons. This talk will review progress in developing an imaging Zero Degree Calorimeter for the EIC. The detector is designed to meet the stringent performance requirements of the EIC for energy and angular resolution for both neutrons and photons over a very large energy range. The fine granularity of the detector opens up the possibility to use machine learning techniques for shower reconstruction. The current status of the design and simulated preformance will be shown.
One of the primary goals of the EIC is to deepen our understanding the multidimensional structure and distribution of gluons within nucleons and nuclei. The recent discovery of entanglement enabled spin interference in photonuclear heavy-ion collisions offers a powerful new avenue for exploring gluon distributions at high energy with RHIC and the LHC in the years leading up to the EIC. Most importantly, these novel polarization dependent observables provide direct access to information for constraining gluon transverse spatial distribution inside large nuclei. This poster discusses calculations of polarization dependent diffractive $J/\psi$ production at RHIC and LHC energies using the color glass condensate effective theory. The predictions have been extended to EIC energies and conditions, showing that strong azimuthal modulations are expected due to the initial photon polarization in diffractive photonuclear production at the EIC. In this poster, we assess the practicality and feasibility of these measurements considering the design characteristics of the EPIC experiment detector. As a final note, we comment on the complementary physics insights that can be gained from similar measurements via other vector meson production channels at existing experiments and at the future EIC.
The origin of hadron masses cannot be attributed to the Higgs mechanism alone. On top of that, the spontaneous breaking of chiral symmetry potentially restored at extremely high temperatures, plays an important role. Low-mass vector mesons (ρ, ω, φ) are highly sensitive to chiral symmetry restoration effects, and their electromagnetic spectral function is expected to be modified in Pb-Pb collisions as compared to the “vacuum” spectral function measured in pp collisions. Chiral symmetry restoration can manifest itself in two different ways: a pole-mass shift or a broadening of the spectral function.
In this poster, the feasibility study for measuring ω meson in the dimuon channel using the ALICE forward muon tracker is presented. Results obtained using Run 2 data are used as a reference for studying the expected performance in Run 3 using the upgraded forward tracker. The measurement will be performed using the data that will be collected this year during the heavy-ion run.
Exploring the space-time extent of particle production is an important goal of heavy-ion physics, and substantial effort has been made in order to understand the underlying physics behind the experimental observations of non-Gaussian behavior. In experiments, femtoscopic (momentum) correlations are utilized to gain information about the space-time geometry of the particle emitting source. Various experiments from SPS through RHIC to LHC measure Bose-Einstein quantum-statistical correlations. While early on the Gaussian assumption worked well when extracting source parameters, with precise data of today more advanced assumptions have to be used. This strongly affects our understanding of the collision energy dependence of source parameters, and relatedly the equation of state: a non-monotonic behavior in source widths may be overshadowed (or, to the contrary, caused) by the mixing of change in shape and in size. In this talk we review recent measurements, present several possible physical explanations (including critical behavior, anomalous diffusion and resonances) and their implications on various stages of evolution as well as the search for the critical endpoint of QCD.
In Heavy-Ion Collisions (HIC), the high temperature nuclear matter is expected to be produced with a chiral imbalance. The presence of a chiral imbalance can be detected in HIC by looking at observables related to the Chiral Magnetic Effect (CME). In off-central collisions,the nuclear matter also posses a very large vorticity. In order to preserve causality, a rotating system can not extend to infinity but must be confined in a finite region, for instance by means of a boundary condition.
We study a free gas of massless fermions confined in a finite cylinder in the presence of a constant magnetic field and with chiral imbalance. We impose the boundary condition using the MIT bag model and we compute the CME. We find that in a cylinder with fixed radius the CME current is decreasing for magnetic fields below a critical value that depend on the radius. Estimates and consequences in HIC are discussed.
Measurements of heavy-flavor hadron production play an important role in the testing of pQCD calculations, and represent a critical component in studies of the quark-gluon plasma (QGP) created in heavy-ion collisions. We study three different D0-tagged jet axes, with varying degrees of sensitivity to wide-angle radiation: Standard, Soft Drop groomed, and Winner-Take-All (WTA). By considering the angles between different axes, we can study the radiation pattern inside the reconstructed jets, thus providing insight into the associated fragmentation and hadronization processes. In this poster, we present the first D$^0$-tagged jet axes difference studies carried out in pp collision at 5.02 TeV with the ALICE experiment at the LHC, with jets of transverse momentum $p_{\mathrm{T,jet}} > 5 \: \mathrm{GeV}/c$ and D$^0$-mesons with $p_{\mathrm{T,D^0}} > 2 \: \mathrm{GeV}/c$. The measurements include the radial distributions of D$^0$ mesons with respect to the jet axis, $\Delta R_{\mathrm{D,jet}}$, as well as a study of the opening angle, $\Delta R_{\mathrm{axis}}$, between various definitions for the axis of a D$^0$-tagged jet. We compare these results with those obtained from the inclusive, gluon-dominated, sample of jets. These measurements, at relatively low jet momentum, are sensitive to heavy-flavor production mechanisms and will serve as important groundwork for an in-depth understanding of charm-quark diffusion in the QGP.
NA61/SHINE has measured the first deuteron production in proton-proton interactions at 158 GeV/c (sqrt(s) = 17.3 GeV). These measurements will be presented and compared to different nuclear formation models. The two most prevalent formation models—the thermal and coalescence models—are based on different underlying physics. A better understanding of (anti)nuclei production mechanisms is needed, which drives the effort to analyze high-statistics data sets from fixed-target experiments. Additionally, new updated measurements of proton, antiproton, π±, and K± spectra will be showcased, along with unique measurements of Omega and K0s production in p+p interactions.
Deuteron production measurements are important for understanding cosmic-ray antinuclei. The detection of cosmic antinuclei holds the potential to be a breakthrough approach for identifying dark matter signatures. The main source of cosmic antinuclei background are interactions between cosmic-ray protons and interstellar hydrogen gas. Gaining a deeper insight into deuteron production in p+p interactions is an essential first step in modelling these astrophysical processes. Furthermore, modeling of light antinuclei production typically requires antiproton production cross sections as input. Precise antiproton measurements are crucial. The updated hadron spectra exhibit significantly reduced statistical uncertainties and extend the phase space coverage in rapidity and transverse momentum compared to earlier measurements. These advancements can be employed to refine our understanding of proton-proton interactions.
Besides the traditional flow studies of individual flow amplitudes $v_n$, independent information about all stages in heavy-ion evolution can be extracted from multi-harmonic correlations of flow amplitudes. The simplest realization is Symmetric Cumulants (SC), which correlate the same-order moments of two or more flow amplitudes. In recent studies, it was demonstrated that SC can reveal the details of the differential temperature dependence of specific shear viscosity ($\eta/s$) of quark--gluon plasma, while individual $v_n$ amplitudes are sensitive only to the average values $\langle\eta/s\rangle$.
The generalization of SC to correlations involving different-order moments of flow amplitudes is not trivial, and it was accomplished only recently. These generalized flow observables are dubbed Asymmetric Cumulants (AC), and they by definition extract new and independent information in flow analyses that is not accessible either to $v_n$, nor to SC observables.
In this contribution, the first feasibility study for centrality dependence of AC is presented for data-taking conditions in CBM experiment at FAIR.
Heavy quarks are produced in hard partonic scatterings at the very early stage of heavy-ion collisions and they experience the whole evolution of the Quark-Gluon Plasma medium. Femtoscopic correlations, i.e. two-particle correlations at low relative momentum, are sensitive to the final-state interactions as well as to the extent of the region from which the correlated particles are emitted. A study of such correlations between charmed mesons and identified charged hadrons could shed light on their interactions in the hadronic phase and the interaction of charm quarks with the medium.
In this poster, we will present the first measurement of femtoscopic correlations between $D^0-{\pi}$, $D^0-K$, and $D^0-proton$ pairs at mid-rapidity in Au+Au collisions at ${\sqrt{s_{NN}}}$ = 200 GeV using the data taken in the year 2014 and 2016 by the STAR experiment. $D^0$ mesons are reconstructed via the $K^{-}-{\pi}^{+}$ decay channel using topological criteria enabled by the Heavy Flavor Tracker with excellent track pointing resolution. We will present the femtoscopic correlation function for $D^0$ transverse momentum above 1 GeV/c in the $0-80\%$ centrality. We will also compare the experimental results with available theoretical models and discuss physical implications.
Accurate knowledge of the strong interaction between charged kaons and (anti)deuteron is a missing piece of information in the field of the low-energy (anti)kaon-nucleon interactions for more than 40 years. The interaction between charged kaons and (anti)deuterons is a complex subject at both experimental and theoretical levels. From the experimental point of view, so far scattering cross sections at intermediate momenta were performed. Specific information on the strong interaction can be accessed also via kaonic deuterium X-ray spectroscopy but such measurements are challenging due to the available detection efficiency. One of the missing information on $\mathrm{K^{-} d}$ and $\mathrm{K}^{+} \mathrm{d}$ interactions is their scattering lengths. Due to the lack of direct experimental measurements, theoretical predictions for $\mathrm{K}^{-} \mathrm{d}$ have been made based on input from kaonic hydrogen measurements. There are no published theoretical predictions for the scattering length of $\mathrm{K^{+} d}$. The first femtoscopic measurement of $\mathrm{K}^{+} \mathrm{d} \oplus \mathrm{K}^{-}\overline{\mathrm{d}}$ and $\mathrm{K}^{-} \mathrm{d} \oplus \mathrm{K}^{+} \overline{\mathrm{d}}$ in Pb--Pb collisions at $\sqrt{s_{\rm NN}}=5.02\ \mathrm{TeV}$ are presented. In this study, the scattering lengths of $\mathrm{K}^{+} \mathrm{d}$ and $\mathrm{K}^{-} \mathrm{d}$ pairs associated with strong final-state interactions, as well as the source radii of the kaon-deuteron pairs were determined using the Lednický-Lyuboshitz model. The interaction parameters obtained for $\mathrm{K}^{+} \mathrm{d} \oplus \mathrm{K}^{-} \overline{\mathrm{d}}$ and $\mathrm{K}^{-} \mathrm{d} \oplus \mathrm{K}^{+} \overline{ \mathrm{d}}$ are compared with the values available in the literature to discriminate between the different theoretical approaches.
The sPHENIX detector is designed to study fundamental properties of the quark-gluon plasma created in heavy ion collisions at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. The sPHENIX Event Plane Detector (sEPD) is constructed both in the forward and backward rapidity region with the coverage of 2.1 $<|\eta|< $4.9. The essential role of the sEPD is to provide event plane determination with high resolution as well as centrality determination in Au+Au collisions. This poster will discuss the first performance results of the sEPD, covering cosmic tests of the sectors and calibration results from the first sPHENIX run. Implications for potential physics measurements will be discussed.
The first results on identified hadron spectra produced in central Xe+La collisions at SPS will be presented. The kinematic distributions and measured multiplicities of identified hadrons will be compared with previously released by NA61/SHINE results on p+p, Be+Be, Ar+Sc and NA49 Pb+Pb results, as well as with available world data.
Obtained results, and in particular ratio of positively charged kaons to pions, are crucial for the understanding of the phenomena of the onset of deconfinement and the onset of fireball, which are one of the main studies in the strong interactions program of the NA61/SHINE experiment.
During the early hydrodynamic phase, the chemical composition of the quark-gluon plasma (QGP) is still largely unknown. Here we study the effects of quark chemical equilibration on the QGP using a novel model of viscous hydrodynamic evolution in partial chemical equilibrium. In this model, we initialize the QGP in a completely gluon dominated state, as motivated by the success of gluon saturated initial condition models. Local light and strange quark production during the hydrodynamic phase is simulated through the evolution of time-dependent fugacities for each quark flavor, with the timescales set as free parameters to compare different rates of equilibration. This impacts the system through the equation of state, which we have constructed to depend on the quark flavor content throughout the QGP.
Using this model, implemented in the MUSIC hydrodynamic code and iS3D particlization code, we have simulated ensembles of Pb+Pb and Au+Au collision events with varying quark chemical equilibration times. We discuss the observed dependence of hadronic and electromagnetic observables on the equilibration time. We also examine the impact of quark chemical equilibration on the transport properties of the QGP, and show preliminary results for a Bayesian model-to-data comparison that will simultaneously constrain the equilibration times and transport coefficients of the QGP.
Higher order flow harmonics provide a powerful probe of the initial geometry of heavy ion collisions, as well as the properties of the quark-gluon plasma produced in these collisions, including the transport coefficients and the degree of collective behavior. This poster presents higher order flow harmonics measurements in PbPb collisions at $\sqrt{s_{_{\mathrm{NN}}}} = 5.02$~TeV using data from the CMS experiment. We will discuss the centrality dependence of flow harmonics up to order 10 and compare them to theory calculations and lower order measurements.
Forward and backward rapidity regions are rich laboratories to explore several effects which happens to a probe before and after its hard scattering. The large rapidity region may also experiment a different dynamics for strangeness enhancement seen in heavy ion collisions at RHIC and LHC. The PHENIX experiment has a long history of large rapidity measurements with the muon spectrometers covering 1.2$<|\eta|<$2.2 and a forward calorimeter (MPC) covering 3.1$<|\eta|<$3.8. The addition of a pre-shower detector, the MPC-ex in front of the MPC, allows the identification of $\pi^0$ in a broad momentum range covering a Bjorken-x region between $10^{-3}-10^{-2}$. This presentation will report two measurements: i)$\phi$ meson nuclear modification using the muon spectrometer in $d$+Au, Cu+Au and Au+Au which can explore how strangeness are affected by initial and final state effects and its behavior in QGP at large rapidity; ii) $\pi^0$ nuclear modification factor in $d$+Au collisions which are sensitive to parton shadowing and gluon saturation.
Various interesting phenomena have been predicted to occur in a quark-gluon plasma produced in relativistic heavy-ion collisions due to a strong magnetic field which is also generated in these collisions. However, none of these predictions has been convincingly confirmed experimentally yet. So, the question is why? Our aim is to systematically discuss the problem of magnetic field generation. In particular, we argue that the currents induced in the plasma, which have been expected to sustain the magnetic field throughout the plasma lifetime, are much smaller than expected. This happens because the quark-gluon plasma is initially mostly composed of gluons while electrically charged quarks appear with a delay.
The sPHENIX experiment at RHIC will begin commissioning with Au+Au data in Spring 2023. The Monolithic Active Pixel Sensor (MAPS) based Vertex Detector (MVTX), the Intermediate Silicon Tracker (INTT) and the Time Projection Chamber (TPC) at sPHENIX can provide high precision primary/displaced vertex and track reconstruction in the pseudorapidity region of $|\eta| \le 1.1$. The sPHENIX ElectroMagnetic Calorimeter (EMCal) and Hadronic Calorimeter (HCal), used for the first time at RHIC, will provide good energy measurements for full jet reconstruction. sPHENIX will enable an unprecedented series of high precision heavy flavor hadron and jet measurements at sPHENIX in 200 GeV p+p, p+Au and Au+Au collisions. In particular, the heavy flavor hadron inside jet production can provide vital information about the heavy quark hadronization process and how such process gets modified in a nuclear medium. Less recombination contribution to the hadron production is expected at RHIC compared to the Large Hadron Collider (LHC) measurements, which makes these measurements an unique approach to explore the universality of heavy quark fragmentation functions in different nuclear environments. We will present the performance projection of the D-meson inside jet reconstruction, the hadron-jet relative kinematic variable distributions, and projections in 200 GeV p+p and Au+Au simulations with realistic sPHENIX detector performance. We will also report on the status of the heavy flavor physics analyses.
Heavy quarks serve as effective probes of relativistic heavy-ion collisions as they are created in the initial stages of the collision event and exist at all stages. We study the dynamics of heavy flavors using a hybrid framework that incorporates the MARTINI event generator, pythia8.1 for the initial production of heavy quarks, and Langevin dynamics to describe the evolution of heavy quarks in a 3+1-D expanding QGP medium. We include the interactions of heavy quarks with the medium constituents through the heavy quark transport coefficients. The space-time expansion of the QGP medium is described using the hydrodynamical approach MUSIC with IP-Glasma initial state and Bayesian-quantified viscous coefficients of the strongly-interacting matter. The properties of the QGP medium are probed by analyzing the heavy meson nuclear modification factor and flow coefficient for Pb+Pb collision. In this work utilizing for the first time IP-Glasma fluctuating initial states and hydrodynamics tuned to a global Bayesian analysis, we show that the observables associated with D-mesons are strongly influenced by the IP-Glasma initial state and bulk evolution. Additionally, we provide new insights into the interaction strength of charm quarks in the expanding medium, including elastic collisional processes with medium constituents, gluon emission processes, and non-perturbative interactions.
The sPHENIX experiment will begin commissioning in Spring 2023 at the Relativistic Heavy Ion Collider (RHIC) at BNL, presenting a unique opportunity to study QGP properties using jets and heavy quarks with unprecedented precision. The successful construction and deployment of the three-layer Monolithic-Active-Pixel-Sensor (MAPS) based VerTeX detector (MVTX) for the sPHENIX experiment in 2023 enables precise measurements of heavy bottom quark jets (b-jets) and B-hadrons produced in high-energy heavy-ion Au+Au and p+p collisions at RHIC. These measurements offer a unique set of observables given the large bottom quark mass. These measurements will span an unexplored kinematic regime, particularly at low p$_T$ where mass-dependence effects in QGP are expected to be significant, while the underlying backgrounds are also expected to be high.
The MVTX detectors serve as the innermost tracking system of the sPHENIX experiment, covering 2.5-4.0 cm radially and a pseudorapidity range of $|\eta|$ < 2. With its very fine 27 $\mu$m x 29 $\mu$m pixels, the MVTX detector can identify heavy hadron decay secondary vertices and heavy flavor jets in heavy ion collisions with high efficiency and purity. In this poster, we will highlight the impact of the MVTX detector on future heavy flavor measurements, including b-hadrons and b-jets in heavy ion collisions and will present the status of the MVTX detector commissioning.
The early stage of high-energy nuclear collisions is dominated by strong gluon fields called the evolving Glasma. This stage can be probed by heavy quarks (HQs), charm and beauty, since they are produced almost immediately by hard scatterings. We study the propagation of HQs in the evolving Glasma fields, by solving the relativistic kinetic equations that couple the HQs to the fields themselves. We analyze the impacts of this (so far) neglected dynamics on observables, namely the nuclear modification factor and the elliptic flow. We find that both these quantities are affected in a substantial way by the propagation in the early gluon fields.
Owing to its spectrometer acceptance, which is complementary to the other
LHC experiments, LHCb is collecting several fixed-target and ion collision sam-
ples, providing unique inputs to theoretical models in poorly explored kinematic
regions. In this contribution, the impact of the ongoing and foreseen upgrades
of the LHCb experiment on the ions and fixed-target physics programme are
discussed, notably including the installation of tracking station inside the mag-
net and the replacement of some tracker detectors to avoid saturation in central
lead-lead collisions.
It is well-known that vorticity induces polarization in quantum plasmas via chiral vortical effect (CVE). Besides the CVE-induced axial current, vorticity gives rise in the presence of a net baryon charge also to a helicity current via the novel helical vortical effect (HVE) [1], which is the focus of the present talk. The HVE and CVE applied together naturally explain the matter/anti-matter polarization asymmetry seen in the experimental data for hyperons reported by STAR [2].
[1]: Victor E. Ambrus, M. N. Chernodub, Eur. Phys. J. C 83 (2023) 111. DOI: 10.1140/epjc/s10052-023-11244-0.
[2]: Victor E. Aambrus, M. N. Chernodub, Eur. Phys. J. C 82 (2022) 61. DOI: 10.1140/epjc/s10052-022-10002-y.
We investigate the hydrodynamic helicity polarization of Λ hyperons, defined as the projection of the spin polarization vector along the directions of particle momenta, at RHIC-BES energies by utilizing the relativistic (3+1)D CLVisc hydrodynamics framework with SMASH initial conditions. As opposed to local spin polarization at high energy collisions, our hydrodynamic simulations demonstrate that the helicity polarization induced by the kinetic vorticity dominates over other contributions at intermediate and low collision energies. Our findings provide an opportunity to probe the fine structure of local kinetic vorticity as a function of azimuthal angle at intermediate and low collision energies by mapping our predictions to the future measurements in experiments. In addition, we also study the vorticity contribution to 00 component of the spin density matrix for final $\phi$ mesons $\overline{\rho}_{00}^{\phi}$.
In this talk we review the hadronization of jets in various vacuum collision systems using the JETSCAPE event generator and Hybrid Hadronization. Hybrid Hadronization combines quark recombination, applicable when distances between partons in phase space are small, and string fragmentation appropriate for dilute parton systems. It can therefore smoothly describe the transition from very dilute parton systems like to full AA collisions. We test this picture by using JETSCAPE to generate jets in various systems. Comparison to experimental data for several observables at multiple energies allows for a precise calibration of vacuum baseline parameters in JETSCAPE and Hybrid Hadronization. We use charged hadron, identified hadron and jet spectra in a Bayesian calibration to find the best parameter tune. The inclusion of further observables in p+p and e+e- in the future is discussed.
Relativistic hydrodynamics has been successful in describing space-time evolution of matter created in high-energy nuclear collisions. It is conventionally supposed that the created matter starts to behave as fluids all at once at a certain initial time. It is, however, not at all trivial from which stage after the collision the fluid picture can be applied to the system. According to the hydrodynamization theory [1], any solutions of hydrodynamic equations converge to an attractor. Thus, hydrodynamic description might be justified anyway even starting from the system far away from local equilibrium. Do we really describe space-time evolution of the system using hydrodynamics even when the system is far away from local equilibrium? In this study, we address this issue from a point of view of causality.
A recent study shows necessary and sufficient conditions for the solutions to be causal in non-linear relativistic hydrodynamic equations [2]. When they are applied to numerical hydrodynamic simulations, it turns out that causality tends to be violated at the early time and/or in peripheral regions [3]. This indicates that violation of causality has something to do with how far the system is away from local equilibrium. Motivated by these observations, we scrutinize a one-dimensionally expanding conformal system from a view point of causality and constrain the initial conditions whose solutions by no means violate the causality. We first define the degree of non-equilibrium and then describe its time evolution solving the Muller-Israel-Stewart type constitutive equation in one-dimensionally expanding system. We find that it is acausal in fact when the system is far away from local equilibrium. Using these solutions, we quantify a range of the inverse Reynolds number in which hydrodynamic description is justified from a view point of causality. This sheds light on the understanding of initial stages in high-energy nuclear collisions.
References:
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[2] F.S. Bemfica et al., Phys. Rev. Lett. 126, 222301 (2021).
[3] C. Plumberg et al., Phys. Rev. C 105, L061901 (2022).
Relativistic hydrodynamics has been widely employed in high energy nuclear physics, with applications in heavy-ion collisions, neutron star mergers and coalescing matter in black holes [1]. Due to the acausality and instability of relativistic Navier-Stokes (NS) theory [2], one usually employs Israel-Stewart-like (IS) formulations of fluid dynamics [3] in which the constitutive relations for the dissipative currents are replaced by relaxation type equations. This comes at the expense of a more complex structure of the partial differential equations being solved, which renders the assessment of features of solutions in the non-linear regime very intricate. More recently, the Bemfica-Disconzi-Noronha-Kovtun (BDNK) theory has emerged [4], where theorems for causality, linear stability and existence of solutions can be rigorously established, but unconventional matching conditions are required. For all of the aforementioned theories, transport coefficients play a fundamental role. However, their computation is usually a very non-trivial task, even in the context of Kinetic Theory. We show that this difficulty can be circumvented for a system composed of classical ultra-relativistic scalar particles weakly interacting via a quartic potential. Then, the specific form of the cross-section [5] allows for the computation of transport coefficients without approximations beyond the power-counting scheme of the corresponding hydrodynamic theory. In this contribution, we calculate all transport coefficients of NS, BDNK and IS theories and demonstrate, in a Bjorken flow scenario, that NS and BDNK theories are pathological for large gradients and thus cannot be used to describe the early stages of heavy ion collisions. For BDNK and IS theories, attractor solutions are also analyzed.
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[5] G. S. Denicol and J. Noronha. arXiV:2209.10370
Under the extreme conditions of relativistic heavy-ion-collisions hypernuclei are created with large abundancies. Hypernuclei measurements provide insights into the equation-of-state of hadronic matter at high net-baryon densities, as well as into hyperon-nucleon and hyperon-hyperon-interactions. The Compressed Baryonic Matter (CBM) experiment at the future Facility for Anti-Proton and Ion Research (FAIR) in Darmstadt offers the perfect conditions to explore the production of hypernuclei. The excitation function of hypernucleus production exhibits its maximum in the FAIR energy range. In combination with the foreseen high interaction rates of up to 10 MHz, an exceptionally high amount of hypernuclei such as e.g. $^{4}_{\Lambda}$H and $^{5}_{\Lambda}$He will be created, and even very rare double hypernuclei like ${}^{6}_{\Lambda\Lambda}$He are expected with sizeable statistics.
The reconstruction of the hypernuclei-3-body-decay was implemented into the CBM reconstruction software and optimized with respect to important performance indicators. In addition, the reconstruction was performed with a neural network. Expected efficiencies and signal-to-background-ratios were calculated with both approaches for a reliable estimation of the number of reconstructable hypernuclei. Systematical uncertainties were estimated based on simulations with different transport models (e.g. PHQMD), taking into account the signal extrapolation to the full rapidity and transverse momentum range. The experimental sensitivity to properties of hypernuclei, such as their lifetime, was evaluated. Results for $^{3}_{\Lambda}$H will be discussed in detail. Reconstructed mass spectra for $^{4}_{\Lambda}$H, $^{4}_{\Lambda}$He and $^{5}_{\Lambda}$He will be shown in addition. (Work supported by DFG-grant BL 982/3-1)
The observation of hyperon polarization has revealed the existence of large vorticities in the medium created by heavy-ion collisions. Global polarization indicates vorticities perpendicular to the reaction plane due to the system's orbital angular momentum, while local polarization indicates vorticities along the beam direction due to anisotropic transverse expansion of the medium. With the high-statistics data collected by the STAR experiment for isobar Ru+Ru and Zr+Zr collisions at $\sqrt{s_{\mathrm{NN}}} = 200$ GeV, we present the measurements of global polarization for $\Lambda$, $\bar{\Lambda}$, and $\Xi^{\pm}$ as a function of centrality, transverse momentum, pseudorapidity, and azimuthal angle relative to the event plane. These measurements allow us to study possible magnetic field driven effects through the polarization difference between Ru+Ru and Zr+Zr, owing to a larger magnetic field expected in the former.
Furthermore, the first measurements of $\Lambda$ hyperon local polarization along the beam direction relative to the second and third-order event planes in isobar collisions will be presented. Comparisons with previous measurements in Au+Au and Pb+Pb collisions at RHIC and the LHC will be performed to gain important insights into the collision system size and energy dependence of the vorticities in heavy-ion collisions.
Previous measurements have shown a similar trend in the energy dependence between the global polarization and the slope of directed flow, suggesting a strong correlation between the initial tilt of the system and the vorticity [1]. For the first time, this correlation is investigated, and the dependence of the $\Lambda$ global polarization as well as directed flow on the first-order flow vector ($q_1$) is presented in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}} = 19.6$ GeV.
[1] S. A. Voloshin, EPJ Web Conf. 171 (2018) 07002.
Reconstructing hyperons with high purity and high reconstruction efficiency is essential for measurements of hyperon-hyperon correlation and searches for exotic strange hadrons, which are both presently discussed topics in the QCD community. Hyperons can be abundantly produced in Pb-Pb collisions at LHC. However, achieving high purity of reconstructed hyperons with high efficiency is particularly challenging in high charged-particle multiplicity environments.
The conventional reconstruction method of ALICE rejects many hyperon candidates by using topological cuts. To improve the detector performance, we studied the reconstruction of all hyperon candidates based on their decay vertex using the Kalman Filter (KF) technique. Furthermore, a Boosted Decision Tree (BDT) algorithm is applied to the LHC Run 2 Pb-Pb collision data based on the training by the combinatorial background and Monte Carlo simulation. By inputting many parameters for decay vertex reconstruction, we can make finer adjustments than would be possible by simply applying topological cuts manually. Therefore, BDT may help optimize cuts to better separate signal and background. This poster will report the current status of the reconstruction of Λ, Ξ, and Ω with the KF approach, discussing its performance and prospects for the future. These developments are important for the high-luminosity Pb-Pb data-taking campaign foreseen at the end of 2023.
Hypernuclei, bound states of nucleons and hyperons, serve as a natural laboratory to investigate the hyperon-nucleon ($Y$-$N$) interaction, which is an important ingredient for the nuclear equation-of-state. Furthermore, precise measurements of their production yields in heavy-ion collisions are crucial for understanding their production mechanisms. In addition, the strangeness population factor, $S_{\rm 3}=(^{3}_{\Lambda}\mathrm{H}/^{3}\mathrm{He})/(\Lambda/p)$, is of particular interest as it has been suggested to be sensitive to baryon-strangeness correlations and the onset of deconfinement.
The STAR Beam Energy Scan II program provides a unique opportunity to investigate the collision energy and system size dependence of hypernuclei production. In this poster, we present new measurements on the transverse momentum and centrality dependence of $\rm ^{3}_{\Lambda}H$ yields in Au+Au collisions from $\sqrt{s_{NN}}=7.7$ to $27$ GeV. The $\rm ^{3}_{\Lambda}H/\Lambda$ ratio and $S_{3}$ will be presented as functions of collision energy and centrality. These results are compared to model calculations, and their physics implications will be discussed.
Antimatter in cosmic rays is a powerful probe for Dark Matter indirect de-
tection. To constrain the background from secondary antiparticles, produced
during cosmic ray propagation through the interstellar medium, the related cross
sections need to be precisely determined at accelerator facilities. In particular,
being their secondary production suppressed at low energies with respect to
DM signal predictions, light anti-nuclei like anti-deuterium and anti-helium are
smoking guns for exotic sources. The LHCb experiment currently offers a unique
fixed-target facility exploiting the beam energy provided by LHC and can re-
produce cosmic collisions between protons at the TeV scale and gas targets of
helium. In this poster, we will present the implementation of a new particle identification technique optimized for heavy particles like light nuclei, based on
a time-of-flight measurement in the LHCb Outer Tracker detector, with a fo-
cus on the first performance results obtained on data. Applications in future
analyses will also be discussed
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, we use a machine learning approach to identify jet quenching amounts. Jet showering processes, with and without the quenching effect, are simulated with the JEWEL model, and are embedded with thermal backgrounds. 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 measure the jet shape and jet fragmentation functions for jets classified with the neural network outputs, and quantify their in-medium modifications. The results support that the machine learning approach successfully identifies the quenching effect in the presence of the large uncorrelated background of soft particles created in heavy ion collisions.
The collective properties of nuclear structure, such as radii and deformations, leave distinct signatures in the initial and consequently final stages of relativistic heavy-ion collisions. Collisions of deformed nuclear enhance the fluctuations of harmonic flow coefficients $v_n$ and event-wise mean transverse momentum $[p_T]$, therefore offering a viable approach to establish clear correspondences between the structure of colliding nuclei and the final state observables.
We present measurements of $v_n$, $[p_T]$ fluctuations as well as $v_n$-$[p_T]$ correlations from the STAR experiment. Significant differences are observed for [$p_T$] fluctuations and $v_n$-$[p_T]$ correlations between $^{197}$Au+$^{197}$Au and $^{238}$U+$^{238}$U collisions, which can be quantitatively explained by the large prolate deformation of $^{238}$U with $\beta_{2, \mathrm{U}} \sim 0.28$ and $\gamma_{\mathrm{U}} \sim 0$. Striking differences are also observed in isobar collisions of $^{96}$Ru+$^{96}$Ru and $^{96}$Zr+$^{96}$Zr, where ratios of many observables show significant deviations from unity and exhibit rich patterns as a function of centrality. A comparison with hydrodynamic model simulations suggests a large quadrupole deformation in Ru nucleus with $\beta_{2, \mathrm{Ru}} \sim 0.16$ and a large octupole deformation in $^{96}$Zr nucleus with $\beta_{3, \mathrm{Zr}} \sim 0.2$. The non-monotonic dependence of ratios of multiplicity distribution, $v_2$, and $[p_T]$ fluctuations in the mid-central collisions also requires a difference in the surface diffuseness between $^{96}$Ru and $^{96}$Zr in the model
calculations. Combining all these observables, we can precisely constrain the parameters associated with various nuclear deformations in isobar nuclei. Building on our pioneering demonstration of nuclear structure effects, we present a more precise quantitative extraction of the quadrupole and octupole deformation parameters in $^{96}$Ru and $^{96}$Zr nuclei using heavy-ion collisions.