Family of equations of state based on lattice QCD: Impact on flow in ultrarelativistic heavy-ion collisions

Abstract

We construct a family of equations of state within a quasiparticle model by relating pressure, energy density, baryon density, and susceptibilities adjusted to first-principles lattice QCD calculations. The relation between pressure and energy density from lattice QCD is surprisingly insensitive to details of the simulations. Effects from different lattice actions, quark masses, and lattice spacings used in the simulations show up mostly in the quark-hadron phase transition region, which we bridge over by a set of interpolations to a hadron resonance gas equation of state. Within our optimized quasiparticle model we then examine the equation of state along isentropic expansion trajectories at small net baryon densities, as relevant for experiments and hydrodynamic simulations at RHIC and LHC energies. We illustrate its impact on azimuthal flow anisotropies and on the transverse momentum spectra of various hadron species.

Shear and bulk viscosities of the gluon plasma in a quasiparticle description

“…In local thermal equilibrium, this picture reduces to the quasiparticle model, which was employed successfully to describe lattice QCD equilibrium thermodynamics in [90,[92][93][94]. Thermodynamic self-consistency in this model is a direct consequence of the consistency condition that must be imposed in order to fulfill energy and momentum conservation in the kinetic theory [95,101].…”

“…The entropy density s in the QPM (cf. [91,92]) was calculated by using the parametrization (5) for G 2 (T ), entering also the viscosities, such that results on equilibrium thermodynamics for the pure gluon plasma obtained in lattice QCD are reproduced (see Fig. 1).…”

“…Thus, T is the only thermal variable characterizing properties of the system. The QPM was successfully employed to quantitatively describe lattice QCD results of equilibrium thermodynamics such as the EoS and related quantities [90][91][92][93][94]. In the following, we apply this model to systems exhibiting small departures from thermal equilibrium by using the results of an effective kinetic-theory approach [71,72] for shear and bulk viscosities derived for a quasiparticle system in [95].…”

Viscosities in the Gluon-Plasma within a Quasiparticle Model

“…(2) evaluated for b 0 (x, p) in the local rest frame with T µν (0) = ǫu µ u ν −P(g µν −u µ u ν ), the quasiparticle model expressions for energy density ǫ and pressure P are recovered, cf. [14,16]. Moreover, Eq.…”

“…The underlying quasiparticle model (QPM) was successfully tested to describe lattice QCD results of the EoS [14,15]. In the QPM, gluon and quark quasiparticles obey dispersion relations, where the entering self-energies Π, in general, depend on temperature T and chemical potential µ both explicitly and also implicitly via a phenomenological effective coupling G 2 (T, µ) [16].…”