The charged-particle's final state spectrum is derived from an analytic perturbative solution for the relativistic viscous hydrodynamics. By taking into account the longitudinal acceleration effect in relativistic viscous hydrodynamics, the pseudorapidity spectrum describes well the nucleusnucleus colliding systems at RHIC and LHC. Based on both the extracted longitudinal acceleration parameters λ * and a phenomenological description of the λ * , the charged-particle's pseudorapidity distributions for √ s N N = 5.44 TeV Xe+Xe collisions are computed from the final state expression in a limited space-time rapidity η s region.

The large values and constituent-quark-number scaling of the elliptic flow of low- D mesons imply that charm quarks, initially produced through hard processes, might be partially thermalized through strong interactions with quark-gluon plasma (QGP) in high-energy heavy-ion collisions. To quantify the degree of thermalization of low- charm quarks, we compare the meson spectra and elliptic flow from a hydrodynamic model to experimental data as well as transport model simulations. We use an effective charm chemical potential at the freeze-out temperature to account for the initial charm quark production from hard processes and assume that they are thermalized in the local comoving frame of the medium before freeze-out. mesons are sampled statistically from the freeze-out hyper-surface of the expanding QGP as described by the event-by-event (3+1)D viscous hydrodynamic model CLVisc. Both the hydrodynamic and transport models can describe the elliptic flow of mesons at GeV/c as measured in Au+Au collisions at GeV. Though the experimental data on spectra are consistent with the hydrodynamic result at small GeV/c, they deviate from the hydrodynamic model at high transverse momentum, GeV/c. The diffusion and parton energy loss mechanisms in the transport model can describe the measured spectra reasonably well within the theoretical uncertainty. Our comparative study indicates that charm quarks only approach local thermal equilibrium at small , even though they acquire sizable elliptic flow comparable to light-quark hadrons at both small and intermediate .

In relativistic heavy ion collisions, the fluctuations of initial entropy density convert to correlations of final state hadrons in momentum space, through collective expansion of the strongly interacting QCD matter. We ask by using a (3+1)D viscous hydrodynamic program CLVisc whether the nuclear structure, which provides initial state fluctuations as well as correlations, can affect the final state of heavy ion collisions, whether one can find signals of α cluster structure in Oxygen using the final state observables in 16O + 16O collisions at the CERN Large Hadron Collider (LHC). For the initial nucleon distributions in Oxygen nuclei, we have compared 3 different configurations, the tetrahedral structure with four-α clusters, the deformed Woods-Saxon distribution as well as a spherical symmetric Woods-Saxon distribution. Our results show that the charged multiplicity as a function of centrality and the elliptic flow at most central collisions using 4-α structure differs from Woods-Saxon and deformed Woods-Saxon distributions, which may help to identify the α clustering structures in Oxygen nuclei.