Suppression of the LHC $p/\pi$ ratio due to the QCD mass spectrum

TL;DR

This paper explores how including Hagedorn states, massive resonances with exponential mass spectra, can explain the lower proton-to-pion ratio observed at the LHC by modeling multi-particle reactions and chemical equilibrium in the hadron gas.

Contribution

It introduces a Hagedorn state scenario to account for the suppressed p/π ratio at LHC, highlighting the impact of extended mass spectra on particle ratios.

Findings

Hagedorn states help reproduce the observed low p/π ratio

Protons are underpopulated at the transition temperature

The model maintains consistency with K/π and Λ/π+ ratios

Abstract

Recent measurements of the proton to pion ratio at $\sqrt{s}_{NN}=2.7$ TeV by the ALICE collaboration at the LHC have found it to be lower than predictions from thermal fits. In this paper we investigate the role that the extended mass spectrum via Hagedorn states- massive resonances that follow an exponential mass spectrum and possess large decay widths- play in the determination of particle ratios at LHC through a scenario of multi-particle reactions and dynamical chemical equilibrium within the hadron gas phase. We show that it is possible to describe the lower $p/\pi$ ratio at LHC while still obtaining the experimental ratio of $K/\pi$ and $\Lambda/\pi^+$ in the Hagedorn state scenario if the protons are underpopulated at the switching temperature from hydrodynamics to the hadron gas phase.