Hadron production in heavy ion collisions: Fragmentation and recombination from a dense parton phase

TLDR

At high transverse momentum hadron production is well described in perturbative QCD by parton fragmentation. The study discusses hadron production in heavy ion collisions at RHIC and presents a theoretical description of parton recombination for transverse momenta above 2 GeV. The authors model parton recombination for PT>2 GeV, incorporating a parton‑phase flow to compute anisotropic flow v₂. The model predicts that hadrons with PT<5 GeV arise from parton recombination, smoothly transitioning to a statistical description below 2 GeV, and yields spectra, ratios, suppression factors, and v₂ values that agree with a parton phase at 175 MeV and 0.55c radial flow.

Abstract

We discuss hadron production in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC). We argue that hadrons at transverse momenta ${P}_{T}<5\phantom{\rule{0.3em}{0ex}}\text{GeV}$ are formed by recombination of partons from the dense parton phase created in central collisions at RHIC. We provide a theoretical description of the recombination process for ${P}_{T}>2\phantom{\rule{0.3em}{0ex}}\text{GeV}$. Below ${P}_{T}=2\phantom{\rule{0.3em}{0ex}}\text{GeV}$ our results smoothly match a purely statistical description. At high transverse momentum hadron production is well described in the language of perturbative QCD by the fragmentation of partons. We give numerical results for a variety of hadron spectra, ratios, and nuclear suppression factors. We also discuss the anisotropic flow ${v}_{2}$ and give results based on a flow in the parton phase. Our results are consistent with the existence of a parton phase at RHIC hadronizing at a temperature of $175\phantom{\rule{0.3em}{0ex}}\text{MeV}$ and a radial flow velocity of $0.55c$.