Understanding the $p/\pi$ ratio at LHC due to QCD mass spectrum

TL;DR

This paper investigates the proton to pion ratio in heavy ion collisions at LHC energies, demonstrating that including an extended mass spectrum with Hagedorn states can resolve the discrepancy known as the $p/\pi$ puzzle.

Contribution

The study introduces the inclusion of Hagedorn states in thermal models, successfully reproducing experimental particle ratios at RHIC and LHC energies.

Findings

Extended mass spectrum reproduces particle ratios at RHIC and LHC.

Inclusion of Hagedorn states explains the lower $p/\pi$ ratio at LHC.

Dynamical chemical equilibration achieved with extended spectrum.

Abstract

Thermal fits have consistently reproduced the experimental particles yields of heavy ion collisions, however, the proton to pion ratio from ALICE Pb+Pb $\sqrt{s_{NN}}=2.76$ TeV is over-predicted by thermal models- known at the $p/\pi$ puzzle. Here we test the relevance of the extended mass spectrum, i.e., include Hagedorn states (resonances that follow an exponential mass spectrum and have very short life times) on the $p/\pi$ puzzle. We find that the extended mass spectrum is able to reproduce particle ratios at both RHIC and the LHC as well as being able to match the lower $p/\pi$ ratio at the LHC through dynamical chemical equilibration.