Cooper-Frye spectra of hadrons with viscous corrections including feed down from resonance decays

TL;DR

This paper introduces a method to calculate hadron spectra with viscous corrections, incorporating resonance decays and feed-down effects, applicable in ultra-relativistic heavy ion collision simulations.

Contribution

It provides explicit formulas for resonance decay contributions to hadron spectra within relativistic fluid dynamics, enabling precomputation and improved modeling of freeze-out processes.

Findings

Resonance decay chains significantly affect pion spectra.

Including heavier resonances alters the predicted spectra.

The method allows for phase separation between chemical and kinetic freeze-out.

Abstract

A method to calculate hadron momentum spectra after feed down from resonance decays in the context of ultra-relativistic heavy ion collisions described by relativistic fluid dynamics is presented. The conceptual setup uses the Cooper-Frye freeze-out integration together with an integral operator describing resonance decays. We provide explicit expressions for the integration over the freeze-out surface for a smooth and symmetric background solution, as well as for linearized perturbations around it. A major advantage of our method is that many integrals can be precomputed independently of a concrete hydrodynamic simulation. Additionally, we examine the influence of adding heavier resonances to the decay chain on the spectrum of pions and show how to include a phase with partial chemical equilibrium in order to separate the chemical from the kinetic freeze-out.