Fast Equilibration of Hadrons in an Expanding Fireball

TL;DR

This paper proposes a dynamical model incorporating Hagedorn states to explain rapid chemical equilibration of hadrons in an expanding fireball, aligning well with RHIC experimental data.

Contribution

It introduces a new scheme using master equations and Hagedorn states to achieve fast chemical equilibration in hadron gases, improving upon previous models.

Findings

Hagedorn states significantly accelerate chemical equilibration times.

The model matches observed particle ratios at RHIC.

Rapid equilibration occurs for both overpopulated and underpopulated Hagedorn resonances.

Abstract

Due to long chemical equilibration times within standard hadronic reactions during the hadron gas phase in relativistic heavy ion collisions it has been suggested that the hadrons are "born" into equilibrium after the quark gluon plasma phase. Here we develop a dynamical scheme in which possible Hagedorn states contribute to fast chemical equilibration times of baryon anti-baryon pairs (as well as kaon anti-kaon pairs) inside a hadron gas and just below the critical temperature. Within this scheme, we use master equations and derive various analytical estimates for the chemical equilibration times. Applying a Bjorken picture to the expanding fireball, the kaons and baryons as well as the bath of pions and Hagedorn resonances can indeed quickly chemically equilibrate for both an initial overpopulation or underpopulation of Hagedorn resonances. Moreover, a comparison of our results to $(B+\bar{B})/\pi^{+}$ and $K/\pi^{+}$ ratios at RHIC, indeed, shows a close match.