Constraining the initial stages of ultrarelativistic nuclear collisions

Abstract

One of the many physical questions that have emerged from studies of heavy-ion collisions at RHIC and the LHC concerns the validity of hydrodynamic modelling at the very early stages, when the Quark-Gluon Plasma system produced is still far from isotropy.In this article we review the idea of far-from-equilibrium hydrodynamic attractors as a way to understand how the complexity of initial states of nuclear matter is reduced so that a hydrodynamic description can be effective.

Hydrodynamic attractors in heavy ion collisions: a review

“…where φ ≡ −Π ζ ζ . Thus, the conservation equation, (25), and the MIS equation, (26), represent the set of equations describing the relativistic evolution of a viscous fluid in a Bjorken expanding background. We proceed by expressing the transport coeffecient and the relaxation time in terms of the energy density:…”

“…The previous argument was turned on its head in [25], where the assumption of free streaming at early times was explored by positing the energy density scales with some to-be-determined parameter, β, namely ε ∼ τ −β (the free streaming case has β = 4/3). Using different initial state models and comparing the final state to experimental data, they find that the preferred expansion parameter β is slightly, but distinctly different from the free streaming case.…”

“…Recently, the potential of hydrodynamic attractors as a tool for phenomenological studies has begun to be appreciated. For instance, they have been used to relate initial state energies to the produced particle multiplicity [24,25]. Moreover, recent studies examined the hydrodynamic attractor at finite chemical potential [26,27], tracing the hydrodynamic evolution as trajectories through the QCD phase diagram.…”

Exponential Approach to the Hydrodynamic Attractor in Yang-Mills Kinetic Theory

“…and different theoretical [15][16][17][18][19][20][21][22][23] and phenomenological aspects of the emergence of hydrodynamic attractors [24][25][26][27] have been explored. See [28] for a recent review.…”

Equilibration of the Quark-Gluon Plasma at finite net-baryon density in QCD kinetic theory

“…Phenomenological consequences -We conclude our analysis by studying the phenomenological consequences of our results, for the dynamical description of heavyion collision experiments at RHIC and LHC energies. Neglecting the entropy production during the late stage hydrodynamic expansion, we follow previous works [28,57] matching the asymptotic entropy density (τ s) eq = 4 3…”