Radial and elliptic flow in Pb+Pb collisions at energies available at the CERN Large Hadron Collider from viscous hydrodynamics

Abstract

A comprehensive viscous hydrodynamic fit of spectra and elliptic flow for charged hadrons and identified pions and protons from Au+Au collisions of all centralities measured at the Relativistic Heavy Ion Collider is performed and used as the basis for predicting the analogous observables for Pb+Pb collisions at the Large Hadron Collider at √ s = 2.76 and 5.5 A TeV. Comparison with recent measurements of the elliptic flow of charged hadrons by the ALICE experiment shows that the model slightly over-predicts the data if the same (constant) specific shear viscosity η/s is assumed at both collision energies. In spite of differences in our assumptions for the equation of state, the freeze-out temperature, the chemical composition at freeze-out, and the starting time for the hydrodynamic evolution, our results agree remarkably well with those of Luzum [M. Luzum, Phys. Rev. C 83, 044911 (2011)], indicating robustness of the hydrodynamic model extrapolations. Future measurements of the centrality and transverse momentum dependence of spectra and elliptic flow for identified hadrons predicted here will further test the model and shed light on possible variations of the quark-gluon transport coefficients between RHIC and LHC energies.

Higher harmonic anisotropic flow of identified particles in Pb–Pb collisions with the ALICE detector

“…This figure illustrates how v 2 (p T ), v 3 (p T ) and v 4 (p T ) develop for different particle species in the same centrality range. A clear mass ordering is seen in the low p T region (for p T < 3 GeV/c) for v 2 (p T ), v 3 (p T ) and v 4 (p T ), which rises from the interplay between the anisotropic flow harmonics and radial flow [7,8,9,10]. Radial flow creates a depletion in the particle spectrum at low p T values, which increases with increasing particle mass and transverse velocity.…”

“…Radial flow creates a depletion in the particle spectrum at low p T values, which increases with increasing particle mass and transverse velocity. When this effect is embedded in an environment where azimuthal anisotropy develops, it leads to heavier particles having smaller v n value compared to lighter ones at a given value of p T [7,8,9,10]. Furthermore, the v n (p T ) values show a crossing between pions, kaons and protons, that, depending on the centrality and the order of the flow harmonic, takes place at different p T values.…”

Constraints on the Jet-Medium Coupling from Measurements at RHIC and LHC

“…Below, we study the influence of the details of the jet-medium coupling and the medium background on the simultaneous description of the nuclear modification factor (R AA ) and the high-p T elliptic flow (v 2 ) measured at RHIC and LHC [1,2,3,4] for a radiative pQCD energy-loss ansatz [5]. We contrast media determined via the viscous hydrodynamic approach VISH2+1 [6] with the parton-cascade BAMPS [7] as well as a jet-medium coupling depending on the collision energy with a jet-medium coupling influenced by the energy of the jet, the temperature of the medium and non-equilibrium effects around the phase transition.…”

“…On the other hand, the jet-energy loss of the Hybrid AdS energy-loss ansatz [8] is based on falling strings [1,2,3,4] is compared to a pQCD-based energy loss dE/dτ = κ( √ s NN )E 0 τ 1 e 3/4 ζ 0 v f , including jet-energy loss fluctuations (ζ 0 ) and transverse flow fields (v f ), for a jet-medium coupling that depends on the collision energy (κ = κ( √ s NN )) applying the hydrodynamic backgrounds of VISH2+1 [6] (solid lines) and the parton cascade BAMPS [7] (dashed-dotted lines).…”

“…The jets are spread according to a transverse initial profile specified by the bulk flow fields given by the VISH2+1 and BAMPS backgrounds considered [6,7].…”