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Collective flow in event-by-event partonic transport plus hydrodynamics hybrid approach

2015; American Institute of Physics; Volume: 92; Issue: 1 Linguagem: Inglês

10.1103/physrevc.92.014903

1538-4497

Rajeev S. Bhalerao, Amaresh Jaiswal, Subrata Pal,

Quantum Chromodynamics and Particle Interactions

Complete evolution of the strongly interacting matter formed in ultrarelativistic heavy-ion collisions is studied within a coupled Boltzmann and relativistic viscous hydrodynamics approach. For the initial nonequilibrium evolution phase, we employ a multiphase transport (AMPT) model that explicitly includes event-by-event fluctuations in the number and positions of the participating nucleons as well as of the produced partons with subsequent parton transport. The ensuing near-equilibrium evolution of quark-gluon and hadronic matter is modeled within the $(2+1)$-dimensional relativistic viscous hydrodynamics. We probe the role of parton dynamics in generating and maintaining the spatial anisotropy in the preequilibrium phase. Substantial spatial eccentricities ${\ensuremath{\varepsilon}}_{n}$ are found to be generated in the event-by-event fluctuations in parton production from initial nucleon-nucleon collisions. For ultracentral heavy-ion collisions, the model is able to explain qualitatively the unexpected hierarchy of the harmonic flow coefficients ${v}_{n}({p}_{T})(n=2--6)$ observed at energies currently available at the CERN Large Hadron Collider (LHC). We find that the results for ${v}_{n}({p}_{T})$ are rather insensitive to the variation (within a range) of the time of switchover from AMPT parton transport to hydrodynamic evolution. The usual Grad and the recently proposed Chapman-Enskog-like (nonequilibrium) single-particle distribution functions are found to give very similar results for ${v}_{n}(n=2--4)$. The model describes well both the BNL Relativistic Heavy Ion Collider and LHC data for ${v}_{n}({p}_{T})$ at various centralities, with a constant shear viscosity to entropy density ratio of 0.08 and 0.12, respectively. The event-by-event distributions of ${v}_{2,3}$ are in good agreement with the LHC data for midcentral collisions. The linear response relation ${v}_{n}={k}_{n}{\ensuremath{\varepsilon}}_{n}$ is found to be true for $n=2,3$, except at large values of ${\ensuremath{\varepsilon}}_{n}$, where a larger value of ${k}_{n}$ is required, suggesting a small admixture of positive nonlinear response even for $n=2,3$.