In this symposium, we plan to bring together theoretical and experimental physicists from around the country to discuss new developments in high energy heavy-ion physics with a focus on the below mentioned topics. There will be extensive discussions both on theoretical as well as experimental aspects on these selected signals of heavy-ion collisions. A special emphasis will be given to the latest theoretical findings from the analysis of the available data from different experimental facilities and prospect and feasibility of these measurements in the future experiments at high baryon densities.
The topics of discussion are :
The exclusive photoproduction of vector mesons provides a unique opportunity to constrain the gluon distribution function within protons and nuclei. Measuring vector mesons of various masses over a wide range of rapidity and as a function of transverse momentum provides important information on the evolution of the gluon distribution within nuclei. A variety of measurements, including the exclusive J/$\psi$, $\rho$, and $\Upsilon$ meson production in pPb (at nucleon-nucleon center of mass energies of 5.02 and 8.16 TeV) and PbPb (5.02 TeV) collisions, will be presented as a function of squared transverse momentum and the photon-proton center of mass energy. Finally, compilations of these data and previous measurements are compared to various theoretical predictions.
The Compressed Baryonic Matter (CBM), currently under construction at the Facility for Anti-proton and Ion Research (FAIR) accelerator complex in Darmstadt, Germany aims to explore the QCD phase diagram at high baryon densities. Till date, no dilepton data have been collected in heavy-ion collisions at beam energies between 2A and 40A GeV. CBM aims to perform pioneering measurements of lepton pairs in nuclear collisions, employing both electron ($e^{+}e^{-}$) and muon ($\mu^{+}\mu^{-}$) channels, in the energy domain $\sqrt{s_{NN}}\sim$ 2.7-4.9 GeV, using unprecedented reaction rates of up to 10 MHz. The Muon Chamber (MuCh) sub-system is dedicatedly designed to track the muons pairs coming from the decay of Low Mass Vector Mesons (LMVM) and $J/\psi$. The expected performance in the muon channel is compared in terms of signal significances and background components for nucleus-nucleus (NN) and hadron-nucleus (pN) collisions.
In this contribution, the details of the simulation framework, analysis techniques and results will be presented for the foreseen CBM energies.
The light nuclei such as B, C, O etc. can occur in different stable α-clustered states, as found in the low-energy nuclear structure studies. Recent phenomenological findings suggest that such light nuclei with different exotic shapes can produce large initial-state anisotropies in relativistic nuclear collisions. The electromagnetic radiations, being sensitive to the initial dynamics, are expected to be affected by the initial clustered structures significantly. In this work, we estimate the production and anisotropic flow of photons from most-central collisions of triangular α- clustered carbon and gold at $\sqrt{s_{NN}}=$200 GeV at RHIC using an event-by-event hydrodynamic framework and compare the results with those obtained from unclustered carbon and gold collisions. We find that the thermal photon $v_3$ for most central collisions is significantly large for the clustered case compared to the case with unclustered carbon. In contrast, the elliptic flow parameter ($v_2$) is found to be similar for the two cases. We show that the ratio of anisotropic flow coefficients can be a potential observable to detect the α-clustered structure in the carbon nucleus.
In the pre-equilibrium stage of relativistic heavy-ion collisions, strong quasi-classical gluon fields emerge. These dense, coherent, colored electric and magnetic fields are known as Glasma. Glasma fields evolve, and the lifetime of these strong fields is of the order of the formation and thermalization time of the QGP, typically a short fraction of fm/c. Heavy quarks (HQs) are good probes to study these early stages of high-energy collisions. We aim to study the diffusion of heavy quarks in the evolving Glasma (EvGlasma). Also, we perform a systematic comparison of the diffusion of HQs in the evolving Glasma fields with that of the Markovian-Brownian motion in a thermalized medium of gluons. We observe the superdiffusion of HQs in the EvGlasma fields as the transverse momentum broadening, $\sigma_p$ of HQs increases non-linearly during the very early time. We also find that for a smaller value of saturation scale, $Q_s$, the average transverse momentum broadening is approximately the same for the two cases, but for a larger value of $Q_s$, Langevin dynamics underestimates the $\sigma_p$.
Heavy quarks (HQs) are considered as effective probes to study the evolution of the quark-gluon plasma (QGP). We study the dynamics of HQs in a hot QCD medium with a time-correlated noise, η. We have introduced the effect of memory through η and the dissipative force in the Generalized Langevin equation (GLV). We assume that the time correlations of the colored noise decay exponentially with time, called the memory time, \tau. We have explored the effect of non-zero values of \tau on the nuclear modification factor, R AA, and transverse momentum broadening, \sigma_p of the HQs within the QGP medium. We find that overall memory slows down the momentum evolution of heavy quarks; In fact, transverse momentum broadening and the formation of RAA are slowed down by memory and the thermalization time of the heavy quarks becomes larger. We will discuss the potential impact on other observables.
The recent studies have indicated an existence of a strong magnetic field in non central Heavy Ion Collisions(HICs). Though strong to begin with the field decays fast. It is still possible for the magnetic field to exist in the thermalised Quark Gluon Plasma(QGP) depending on the electrical conductivity of the medium. If a significant amount of magnetic field is present in the medium, it will affect various aspects. We have calculated different diffusion coefficients of Heavy Quark(HQ), a very good probe of QGP, in presence of a strong magnetic field inside a hot QGP in some of our recent works. It is well established that perturbative QCD description is not enough in order to explain certain experimental observations at the low to intermediate $p_T$ region of HQ and at temperatures close to the critical temperature. There are various studies approaching the non-perturbative calculation from various vantage points within the framework of perturbative QCD, like T-matrix and potential approach.
In this present work, we have considered the complex HQ potential in presence of a strong magnetic field in a hot QGP and posed it as effective gluon propagator. The part of the potential which is Yukawa type is responsible for the perturbative and the string part is responsible for the non-perturbative contribution. We calculate the scattering rate of HQ interacting elastically with the medium light quarks/anti-quarks and gluons.and consequently, estimate the various diffusion coefficients for two cases: 1) HQ velocity is along the direction of the magnetic field and 2) HQ velocity in the perpendicular direction to the magnetic field.
We have compared the perturbative diffusion coefficients with their non-perturbative counterparts in presence of a strong magnetic field for the first time. Though the perturbative contribution is always dominant over that due to non-perturbative, the difference between those two is lower at lower temperatures rendering the non-perturbative estimation more important at the lower temperatures. At higher temperatures, the asymptotic freedom enhances perturbative contribution while the lower value of string tension (taken from finite temperature lattice calculations) or confinement reduces non-pertubative effect. All these might have profound effect on various experimental observations.
We analyze the relative yields of different bottomonia and charmonia states produced in Pb+Pb collisions at LHC, within an ideal hadron resonance gas framework. The underlying assumption is the early thermalization and subsequent freezeout of these heavy hadrons resulting in their chemical freezeout at a temperature, significantly higher than that of light and strange hadrons. The systematic dependence of the freezeout temperature on the collision energy and centrality is investigated in detail.
As a result relativistic heavy ion collision in Large Hadron Collider(LHC) at CERN and Relativistic Heavy Ion Collider(RHIC), at Brookhaven National Laboratory(BNL),the constituent of those, namely Quarks and Gluons deconfined for a short amount of time, and its internal(color) degrees of freedom governs its dynamics. The deconfinement of the nuclear matter happens at bizzare temperature of ∼ 150 MeV which results in the emergence of a new state of matter, identified as Quark Gluon Plasma(QGP). A well-established result that deconfined matter is not a free gas of quarks and gluons but rather strongly interacting and correlated system signals to incorporate dissipative hydrodynamics as a tool to extract the properties of this extremely dense matter, QGP, in the form of various transport coefficients. Due to the rapid thermalization of the produced particles as a result of collision, characterizing the plasma state of matter based on the information provided in the final stage becomes a head scratching task.
Heavy quarks are produced in the pre-equilibrium phase i.e. before the formation of QGP. The long relaxation time of heavy quark make it an apt tool to diagnose QGP.
The study of quarks and gluons falls under perturbative QCD as well as non-
perturbative QCD. While the perturbative QCD has been well developed, the
analytical and numerical solution of non-perturbative QCD has still a long way to go. One of the non-perturbative approaches that seem quite promising in the non-perturbative scale is given by Gribov, which later was updated by Zwanziger by formulating renormalizable action at finite temperature, termed as Gribov-Zwanziger(GZ) action. Within the GZ action, the gluon propagator in covariant gauge is expressed as:
$$D^{\mu\nu}(P)=\left[\delta^{\mu\nu}-(1-\xi)\frac
{P^{\mu}P^{\nu}}{P^2}\right]\left(\frac{P^2}{P^4+\gamma_G^4}\right)~,$$
where $\xi$ is the gauge parameter and $\gamma_G$ is termed as the Gribov parameter, which is fixed either by matching the thermodynamic quantities with lattice equation of state or by solving one loop gap equation. I calculated the diffusion coefficient of heavy quark(in gluonic medium) under Gribov prescription and match it with lattice data available in the range $1 \le (T/T_c)\le 5$. We noticed that it has a good agreement with the lattice data.
There have been different proposals for signatures of the formation of a deconfined thermal medium(quark-gluon plasma) in heavy-ion collisions. The suppression of $J/\Psi$ in the deconfined medium is one of the cleanest signals among many other signatures like elliptic flow, jet quenching etc. However, there are very few signals effective for the formation of QGP in small systems such as the systems produced in proton-proton, proton-deuteron and deuteron-deuteron collisions. Here the medium formed is shown to be very short-lived compared to that formed in heavy ion collision as the system undergoes 3-dimensional spherical expansion from the very beginning of the hydrodynamic phase. We model the small systems for different values of sizes of the system after the Gubser flow solution and we infer that the expansion phase is smaller by a factor of at least 2. We then calculate the dissociation probability of $J/\Psi$ through the non-adiabatic evolution of the state using the time-dependent perturbation theory for different values of thermalization time. We find no significant dissociation of J/Psi in small systems in contrast to the systems produced in Au-Au/Pb-Pb collisions, thereby establishing that quarkonia($J/\Psi$) suppression may not be a successful signature for the formation of the thermal medium for proton-proton/proton-deuteron or deuteron-deuteron collisions.
Proton–proton ( pp) collision has been considered a baseline to understand the formation of the primordial matter, the quark-gluon plasma in relativistic heavy-ion (AA) collisions. However, recent experimental findings show QGP-like phenomena in ultra-relativistic (TeV) pp collisions. Such findings require a cautious study of the system produced in pp collisions at relativistic energies. In this work, we investigate the charmonium production in pp collisions at $\sqrt{s} $= 5.02, 7 and 13 TeV energies. Further, we obtain net charmonia yield at various event multiplicities using our UMQS model, which includes color screening, gluonic dissociation, collisional damping, and regeneration mechanisms. Using the UMQS model, we try to explain the normalized $J/\psi$ yield against the normalized charged multiplicity and compare it with the data available for 7 and 13 TeV pp collisions. Here we obtain a net suppression of charmonia at high-multiplicity events, indicating the possible existence of quark-gluon plasma in pp collisions. Details of the model ingredients, method of analysis, and important results will be discussed.
Recent findings of strangeness enhancement and ridge-like structures in pp collisions at the Large Hadron Collider (LHC) have captured much of the scientific interest in the search for QGP-droplets in pp high-multiplicity events. Thus, it is crucial to gather substantial evidence in this new direction. Studying various thermodynamic and transport properties of the matter formed at LHC can give us hints regarding a possible change in dynamics in the systems. We have used the Color String Percolation Model (CSPM), a Quantum Chromodynamics (QCD) inspired theoretical model, to explore this further. The jet quenching parameter (q ̂) has been estimated within the CSPM approach for pp collisions at √s = 5.02 and 13 TeV, Xe-Xe collisions at √(s_NN ) = 5.44 TeV, Pb-Pb collisions at √(s_NN ) = 2.76 and 5.02 TeV. The findings hint at QGP-like medium formation in high-multiplicity pp collisions. In addition, we have also explored the diffusion of charm quark in the deconfined medium with CSPM and estimated the momentum and spatial diffusion coefficients. Finally, we have compared our results with those obtained from various models, such as lattice-QCD. We found that our results reasonably agree with lattice-QCD and other established models, while revealing a hint for QCD medium formation in pp collisions after a threshold in final state multiplicity density.
In presence of magnetic field the transport coefficients of heavy quarks are seen to have a multi-component structure due to which the spatial diffusion splits into
longitudinal and transverse components relative to the direction of magnetic field. Owing to the Einstein's relation, the spatial diffusion is expressed as a ratio of electrical conductivity and susceptibility. The anisotropic property of the spatial diffusion comes in due to the multi-component structure of the electrical conductivity tensor in presence of magnetic field. The results are studied as a function of temperature and magnetic field for D mesons and charm quarks for their relevant temperature ranges.
Several heavy-ion collision experiments at RHIC and LHC have been performed in identifying quark-gluon plasma (QGP) matter. In recent times, non-central heavy-ion collisions are of more interests where very strong magnetic field is produced in the direction perpendicular to the reaction plane. Many theoretical efforts have been made to study the modification of the strongly interacting matter in presence of an external magnetic field.
The heavy quarkonium is one of the important probes to investigate the properties of nuclear matter in presence of finite temperature and magnetic field. Also the time scale of quarkonia formation and the magnetic field generation are of similar order. So the study of heavy quarkonia in presence of magnetic field is of great interest.
In this work we have explored the imaginary part of the Heavy Quark (HQ) potential and subsequently the dissociation of heavy quarkonia at finite temperature and magnetic field. With respect to earlier investigations on this topic, present work contain three new ingredients. First one is considering all Landau level summation, for which present work can be applicable in entire magnetic field domain - from weak to strong. Second one is the general structure of the gauge boson propagator in a hot magnetized medium, which is used here in heavy quark potential problem first time. Third one is a rich anisotropic structure of the complex heavy quark potential, which explicitly depends on the longitudinal and transverse distance. By comparing with earlier references, we have attempted to display our new contributions by plotting heavy quark potential tomography and dissociation probability at finite temperature and magnetic field.
In high energy nucleon-nucleon and heavy-ion (HI) collisions, the heavy quarks (charm and beauty) are produced at the very early stages of the collisions due to their large masses ($m_{c}\approx$ 1.29 GeV/$\it{c}^{2}$ and $m_{b}\approx$ 4.19 GeV/$\it{c}^{2}$). These heavy quark productions are mainly from hard parton-parton scattering with large momentum transfer ($Q^{2}$). The heavy quarks are produced much before the formation of the deconfined state of quarks and gluons called Quark-Gluon Plasma (QGP) at extremely high temperature and/or energy density in ultra-relativistic HI collision. After the production of heavy-quarks, they interact and pass through the QGP medium and hence experience a full evolution of the medium formed in HI collisions. Hence, the measurement of heavy quarks is very important probe to study the properties of QGP in HI collisions and provide a stringent test of perturbative QCD (pQCD) calculation over a wide range of transverse momentum ($p_{T}$). The measurement of heavy quarks in pp collisions serve as a baseline study for the same measurement in HI collisions.
After the discovery of the features of HI collisions such as ridge like effect and strangeness enhancement in high multiplicity pp events at LHC, the physics community started to look for any thermalised medium formation even in small colliding systems. Traditionally, any thermalised medium is not expected to be formed in small systems like proton-proton (pp) and proton-ion (pA) collisions. Here we would like to present the study of Heavy Flavour decay Muons (HFM) at forward rapidity ($2.5
We will present a study of multiplicity dependence of the differential jet shape observable $\rho(r)$ in proton-proton (pp) collisions at $\sqrt{s}$ = 13 TeV using PYTHIA 8 Monash 2013 Monte Carlo simulation. A significant modification of $\rho(r)$ is observed in high multiplicity pp collisions compared to the minimum bias ones. We will discuss the underlying physics mechanisms in PYTHIA 8, responsible for the observed modification.
The origin of rapidity odd directed flow($v_1$) has been understood as a response of the asymmetric distribution of energy and net-baryon density present in the medium at the initial stages of heavy ion collisions. So, the observed splitting of directed flow between baryon and anti-baryon in RHIC BES could be a useful observable to constrain the initial net-baryon profile by model to data comparison. This in turn can enhance our understanding about the mechanism of baryon stopping. In this context, we have proposed an initial condition model of net-baryon and matter deposition which is taken as an input for a multi stage hybrid framework of hydrodynamics evolution and late stage hadronic interaction. In the model calculations we are able to describe the measured splitting of directed flow between baryons($p,\Lambda$) and anti-baryons($\bar{p}, \bar{\Lambda}$) along with $v_1$ of mesons like $\pi^{\pm}, K^{\pm}$ and $\phi$. Even though we have not considered the evolution of other two conserved charges(corresponding to strangeness and electric charge) in our model, still the splitting of $v_1$ between strange and anti-strange particles have been observed at lower collision energies. This effect has been attributed to the employed equation of state which possesses the constraints of strangeness neutrality($n_S=0$) and net electric charge density $n_Q=0.4 n_B$. We will systematically present the model calculations of rapidity, centrality and $p_T$ dependency of measured identified or charged particle's $v_1$ at $\sqrt{s_{NN}} = $ 7.7 GeV to 200 GeV and compare those with experimental data. With the observations from our model calculations, we will explicitly demonstrate the importance to include the conserved charges evolution along with energy density in hydrodynamics simulations of heavy ion collisions.
The two-particle correlations as a function of relative momenta of identified hadrons involving $\mathrm{K^{0}_{S}}$ and $\Lambda/\bar{\Lambda}$ are measured in PbPb collision at $\sqrt{s_{_{\mathrm{NN}}}} =$ 5.02 TeV with the data samples collected by the CMS experiment at the LHC. Such correlations are sensitive to quantum statistics and possible final state interactions between the particles. The shape of the correlation function is observed to vary largely for different particle pairs, revealing the effect of the strong final state interaction in each case. The source radii are extracted from $\mathrm{K^{0}_{S}K^{0}_{S}}$ correlations in different centrality regions and found to decrease from central to peripheral collisions. The strong interaction scattering parameters are extracted from $\mathrm{K^{0}_{S}K^{0}_{S}}$, $\Lambda\mathrm{K^{0}_{S}}\oplus\bar{\Lambda}\mathrm{K^{0}_{S}}$, $\Lambda\Lambda\oplus\bar{\Lambda}\bar{\Lambda}$ and $\Lambda\bar{\Lambda}$ correlations using the Lednicky-Lyuboshits model, and compared with other experimental and theoretical results. The scattering parameters indicate that the $\Lambda\Lambda\oplus\bar{\Lambda}\bar{\Lambda}$ is attractive and that the $\Lambda\mathrm{K^{0}_{S}}\oplus\bar{\Lambda}\mathrm{K^{0}_{S}}$ interaction is repulsive.
A Multi-Phase Transport (AMPT) model has been used extensively to study the dynamics of relativistic heavy-ion collisions at various collision energies. The AMPT model is very sensitive to input parameters; therefore, the choice of these parameters are very important to explain the results from various experiments. The motivation of this study is to find the most suitable input parameters for AMPT model that explains the particle production and bulk properties of the medium formed at various BES energies at RHIC.
In this talk, we will present the $p_{T}$-spectra of identified hadrons ($\pi^{\pm}, K^{\pm},p(\bar{p}),K_{s}^{0}, \Lambda(\bar{\Lambda}$) and $\phi$) in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7-200 GeV obtained from AMPT model and compare it with the available experimental results. We will also present the centrality and energy dependence of particle yields (dN/dy), average transverse momentum ($\langle p_{T} \rangle$), particle ratios, and compare them with experimental data.
The finite baryon density region of QCD phase diagram, conditions which exists inside the core of neutron stars will be explored by upcoming experiments such as CBM and MPD at FAIR and NICA facilities. As one of the key observables, production of strange particles provides insights about the medium expected to be created in the heavy-ion collisions at beam energies spanning this regime. For the optimal utilization of these future facilities, the predictions from various phenomenological and simulation models are essential. In this presentation, we will report the results from study of strange particle production using hybrid UrQMD model employed with different freeze-out prescriptions available.
Nuclear matter at sufficiently high temperature and energy density undergoes a transition to a phase in which quarks and gluons do not remain confined: the quark-gluon plasma (QGP) phase [1]. Such an exotic state of strongly interacting quantum chromodynamics matter can be produced in the laboratory in high-energy heavy-ion collisions, where an enhanced production of strange hadrons is observed. Strangeness enhancement is originally proposed as a key signature to identify the formation of QGP in high-energy heavy-ion collisions [2]. The yield of strange hadrons is one of the various observables, which is sensitive to the system evolved after nuclear collisions. In particular, the resonance particles are also important for probing QGP phase because of their shorter lifetime (a few fm/c), comparable to the medium lifetime, and due to the rescattering and regeneration processes at the freeze-outs, the yields of the resonances may vary with respect to the non-resonance particles. Recent studies of small collision systems at the Large Hadron Collider (LHC) show unambiguous similarities in hadron production between high multiplicity pp, pPb collisions and PbPb collisions [3]. The studies on production of strange hadron and resonances play important roles in characterizing the LHC data in different collision systems.
In this contribution, we investigate the strange hadron and resonance yields using pQCD-inspired multiple-Parton scattering approach-based two different models, EPOS3 including the hydrodynamical evolution of produced particles and AMPT with a String Melting scenario. The results of yield ratios of identified hadrons will be presented for pp, pPb and PbPb collisions at various LHC energies and results will be confronted to the available experimental data to understand the properties of strongly interacting matter produced in heavy-ion collisions in terms of the model parameters.