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Register a new userHeavy-light flavour correlations of anisotropic flows at LHC energies within event-by-event transport approach
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The heavy quarks (HQs) are unique probe of the hot QCD matter properties and their dynamics is coupled to the locally thermalized expanding quark gluon plasma. We present here a novel study of the event by event correlations between light and heavy flavour flow harmonics at LHC energy within a transport approach. Interaction between heavy quarks and light quarks have been taken into account exploring the impact of different temperature dependence of the transport coefficients $D_s$ and $Gamma$. Our study indicates that $v^{heavy}_n-v^{light}_n$ correlation and the relative fluctuations of anisotropic flows, $sigma_{v_{n}}/langle v_n rangle$, are novel observables to understand the heavy quark-bulk interaction and are sensitive to the temperature dependence even to moderate differences of $D_s(T)$, or $Gamma(T)$. Hence a comparison of such new observables for HQ to upcoming experimental data at both RHIC and LHC can put further constraints on heavy quark transport coefficients and in particular on its temperature dependence toward a solid comparison between the phenomenological determination and the lattice QCD calculations.
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A Monte Carlo study of identified particle ratio fluctuations at LHC energies is carried out in the frame work of hij model using the fluctuation variable $ u_{dyn}$. The simulated events for Pb-Pb collisions at $sqrt{s}_{NN}$ = 2.76 and 5.02 TeV and Xe-Xe collisions at $sqrt{s}_{NN}$ = 5.44 TeV are analyzed. From this study, it is observed that the values of $[pi,K]$, $[p,K]$ and $[pi,p]$ follow the similar trends of energy dependence as observed in the most central collision data by NA49, STAR and ALICE experiments. It is also observed that $ u_{dyn}$ for all the three combinations of particles for semi-central and central collisions, the model predicted values of $ u_{dyn}[A,B]$ for Pb-Pb collisions at $sqrt{s}_{NN}$ = 2.76 TeV agree fairly well with those observed in ALICE experiment. For peripheral collisions, however, the model predicted values of $ u_{dyn}[pi,K]$ are somewhat smaller, whereas for $[p,K]$ and $[pi,p]$ it predicts larger values as compared to the corresponding experimental values. The possible reasons for the observed differences are discussed. The $ u_{dyn}$ values scaled with charged particle density when plotted against $langle$N$_{part}$$rangle$, exhibit a flat behaviour, as expected from the independent particle emission sources. For $[p,K]$ and $[pi,p]$ combinations, a departure from the flat trend is, however, observed in central collisions in the case of low p$_{T}$ window when effect of jet quenching or resonances are considered. Furthermore, the study of $ u_{dyn}[A,B]$ dependence on particle density for various collision systems (including proton-proton collisions) suggests that at LHC energies $ u_{dyn}$ values for a given particle pair is simply a function of charged particle density, irrespective of system size, beam energy and collision centrality.
A study of the charged-particle density (number density) in the transverse region of the di-hadron correlations exploiting the existing pp and p$bar{rm p}$ data from RHIC to LHC energies is reported. This region has contributions from the Underlying Event (UE) as well as from Initial- and Final-State Radiation (ISR-FSR). Based on the data, a two-component model is built. This has the functional form $propto s^{0.27}+0.14log(s)$, where the logarithmic (power-law) term describes the component more sensitive to the ISR-FSR (UE) contribution. The model describes the data from RHIC to LHC energies, the extrapolation to higher energies indicates that at around $sqrt{s} approx 100$ TeV the number density associated to UE will match that from ISR-FSR. Although this behaviour is not predicted by PYTHIA~8.244, the power-law behaviour of the UE contribution is consistent with the energy dependence of the parameter that regulates Multiparton Interactions. Using simulations, KNO-like scaling properties of the multiplicity distributions in the regions sensitive to either UE or ISR-FSR are also discussed. The results presented here can be helpful to constrain QCD-inspired Monte Carlo models at the Future Circular Collider energies, as well as to characterize the UE-based event classifiers which are currently used at the LHC.
We develop a macroscopic description of the space-time evolution of the energy-momentum tensor during the pre-equilibrium stage of a high-energy heavy-ion collision. Based on a weak coupling effective kinetic description of the microscopic equilibration process (`a la bottom-up), we calculate the non-equilibrium evolution of the local background energy-momentum tensor as well as the non-equilibrium linear response to transverse energy and momentum perturbations for realistic boost-invariant initial conditions for heavy ion collisions. We demonstrate how this framework can be used on an event-by-event basis to propagate the energy momentum tensor from far-from-equilibrium initial state models, e.g. IP-Glasma, to the time $tau_text{hydro}$ when the system is well described by relativistic viscous hydrodynamics. The subsequent hydrodynamic evolution becomes essentially independent of the hydrodynamic initialization time $tau_text{hydro}$ as long as $tau_text{hydro}$ is chosen in an appropriate range where both kinetic and hydrodynamic descriptions overlap. We find that for $sqrt{s_{NN}}=2.76,text{TeV}$ central Pb-Pb collisions, the typical time scale when viscous hydrodynamics with shear viscosity over entropy ratio $eta/s=0.16$ becomes applicable is $tau_text{hydro}sim 1,text{fm/c}$ after the collision.
The event-by-event fluctuations of suitably chosen observables in heavy ion collisions at SPS, RHIC and LHC can tell us about the thermodynamic properties of the hadronic system at freeze-out. By studying these fluctuations as a function of varying control parameters, it is possible to learn much about the phase diagram of QCD. As a timely example, we stress the methods by which present experiments at the CERN SPS can locate the second-order critical endpoint of the first-order transition between quark-gluon plasma and hadron matter. Those event-by-event signatures which are characteristic of freeze-out in the vicinity of the critical point will exhibit nonmonotonic dependence on control parameters. We focus on observables constructed from the multiplicity and transverse momenta of charged pions. We first consider how the event-by-event fluctuations of such observables are affected by Bose-Einstein correlations, by resonances which decay after freeze-out and by fluctuations in the transverse flow velocity. We compare our thermodynamic predictions for such noncritical event-by-event fluctuations with NA49 data, finding broad agreement. We then focus on effects due to thermal contact between the observed pions and a heat bath with a given (possibly singular) specific heat, and due to the direct coupling between the critical fluctuations of the sigma field and the observed pions. We also discuss the effect of the pions produced in the decay of sigma particles just above threshold after freeze-out on the inclusive pion spectrum and on multiplicity fluctuations. We estimate the size of these nonmonotonic effects which appear near the critical point, including restrictions imposed by finite size and finite time, and conclude that they should be easily observable.
Recent experiments have observed large anisotropic collective flows in high multiplicity proton-lead collisions at the Large Hadron Collider (LHC), which indicates the possible formation of mini quark-gluon plasma (QGP) in small collision systems. However, no jet quenching has been confirmed in such small systems so far. To understand this intriguing result, the system size scan experiments have been proposed to bridge the gap between large and small systems. In this work, we perform a systematic study on both heavy and light flavor jet quenching in different collision systems at the LHC energies. Using our state-of-the-art jet quenching model, which combines the next-to-leading-order perturbative QCD framework, a linear Boltzmann transport model and the (3+1)-dimensional viscous hydrodynamics simulation, we provide a good description of nuclear modification factor $R_{rm AA}$ for charged hadrons and $D$ mesons in central and mid-central Pb+Pb and Xe+Xe collisions measured by CMS collaboration. We further predict the transverse momentum and centrality dependences of $R_{AA}$ for charged hadrons, $D$ and $B$ mesons in Pb+Pb, Xe+Xe, Ar+Ar and O+O collisions at the LHC energies. Our numerical results show a clear system size dependence for both light and heavy flavor hadron $R_{AA}$ across different collision systems. Sizable jet quenching effect is obtained for both heavy and light flavor hadrons in central O+O collisions at the LHC energies. Our study provides a significant bridge for jet quenching from large to small systems, and should be helpful for finding the smallest QGP droplet and the disappearance of QGP in relativistic nuclear collisions.
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