Non-thermal p/pi ratio at LHC as a consequence of hadronic final state interactions

TL;DR

This paper investigates the anomalous p/pi ratio observed at LHC in Pb+Pb collisions, attributing it to hadronic final state interactions, and proposes the ratio as a probe for transition energy density between hydrodynamics and Boltzmann models.

Contribution

It demonstrates that hadronic final state interactions can explain the p/pi ratio deviation and introduces the p/pi ratio as a sensitive observable for transition energy density.

Findings

Final state interactions explain the p/pi ratio deviation.

p/pi ratio can gauge transition energy density.

Transition energy density estimated at 840 ± 150 MeV/fm^3.

Abstract

Recent LHC data on Pb+Pb reactions at sqrt(s_{NN})=2.7 TeV suggests that the p/pi is incompatible with thermal models. We explore several hadron ratios (K/pi, p/pi, Lambda/pi, Xi/pi) within a hydrodynamic model with hadronic after burner, namely UrQMD 3.3, and show that the deviations can be understood as a final state effect. We propose the p/pi as an observable sensitive on whether final state interactions take place or not. The measured values of the hadron ratios do then allow to gauge the transition energy density from hydrodynamics to the Boltzmann description. We find that the data can be explained with transition energy densities of 840 +- 150 MeV/fm^3.