Scaling of elliptic flow, recombination, and sequential freeze-out of hadrons in heavy-ion collisions
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The scaling properties of elliptic flow of hadrons produced in ultrarelativistic heavy-ion collisions are investigated at low transverse momenta, p(T) less than or similar to 2 GeV. Utilizing empirical parametrizations of a thermalized fireball with collective-flow fields, the 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 multistrange hadrons which are beligeved to decouple close to the critical temperature. The resulting elliptic flow from empirical fits at the BNL Relativistic Heavy Ion Collider exhibits transverse kinetic-energy and valence-quark scaling. Utilizing the well-established concept of sequential freeze-out, the scaling at low momenta extends to bulk hadrons (pi, K, p) at thermal freeze-out, albeit with different source parameters compared to chemical freeze-out. Elliptic-flow scaling is thus compatible with both equilibrium hydrodynamics and quark recombination.