Scaling of elliptic flow, recombination, and sequential freeze-out of hadrons in heavy-ion collisions

Abstract

The scaling properties of elliptic flow of hadrons produced in ultrarelativistic heavy-ion collisions are investigated at low transverse momenta, $p_T\lsim 2$\,GeV. Utilizing empirical parameterizations of a thermalized fireball with collective-flow fields, Resonance Recombination Model (RRM) is employed to describe hadronization via quark coalescence at the hadronization transition. We reconfirm that RRM converts equilibrium quark distribution functions into equilibrated hadron spectra including the effects of space-momentum correlations on elliptic flow. This provides the basis for a controlled extraction of quark distributions of the bulk matter at hadronization from spectra of multi-strange hadrons which are believed to decouple close to the critical temperature. The resulting elliptic flow from empirical fits at RHIC exhibits transverse kinetic-energy and valence-quark scaling. Utilizing the well-established concept of sequential freeze-out we find that the scaling at low momenta can be extended to bulk hadrons ($\pi$, $K$, $p$) at thermal freeze-out, and thus result in an overall description compatible with both equilibrium hydrodynamics and quark recombination.