Thermodynamics of heavy-light hadrons

TL;DR

This paper uses lattice QCD simulations to study fluctuations of conserved charges, providing evidence for unobserved hadrons and their impact on the thermodynamics and freeze-out conditions in heavy ion collisions.

Contribution

It offers new lattice QCD results on charm and strange fluctuations, indicating the existence of additional hadrons and refining the understanding of freeze-out parameters.

Findings

Open strange and charm hadrons dissociate near the chiral crossover.

Evidence suggests existence of unobserved hadrons from QCD thermodynamics.

Including extra states lowers freeze-out temperature by 5-8 MeV.

Abstract

Ratios of cumulants of conserved net charge fluctuations are sensitive to the degrees of freedom that are carriers of the corresponding quantum numbers in different phases of strong interaction matter. We calculate second and fourth order cumulants of net charm and strange fluctuations and their correlations with other conserved charges such as net baryon number and electric charge. Simulation are performed on $N_\tau$=6 and 8 lattices using the Highly Improved Staggered Quark (HISQ) action with a light to strange quark mass ratio of 1/20 and having charm quarks treated in the quenched approximation. Analysing appropriate ratios of these cumulants we observe that both open strange and charm hadrons start to get dissociated in the chiral crossover region. We provide indirect evidence for the existence of additional, experimentally yet unobserved open charm and strange hadrons from QCD thermodynamics. This is done by comparing lattice QCD results to Hadron Resonance Gas (HRG) model calculations performed with a hadron spectrum as listed in the Particle Data Tables as well as with a spectrum predicted in the relativistic quark model and observed in lattice QCD calculations. We also discuss the influence of these experimentally yet unobserved states on the determination of freeze-out temperature and chemical potentials from heavy ion collision experiments. We found that including these additional states in the HRG model leads to a systematic 5-8 MeV decrease in the freeze-out temperature of strange hadrons.