Balance of attractive and repulsive hadronic interactions: The influence of hadronic spectrum and excluded-volume effects on lattice thermodynamics, and consequences for experiments

Abstract

Repulsive hadronic interactions play a relevant role in the QCD dynamics, attractive ones being represented by resonance formation. In this study we propose different schemes in order to parameterise repulsive interactions, then being able to extract effective sizes of hadrons from fits to lattice QCD simulations. We find that allowing a difference between the strange and light sectors, strange particles are systematically smaller than light ones with equal mass. The very simple implementation of repulsive interactions would in principle allow to extract precise information about all hadronic species once corresponding lattice observables, sensitive to the species of interest, are provided. With the parameterisation which best reproduces lattice data there is also a good description of experimental yields measured by ALICE and STAR experiments.

Flavor-dependent eigenvolume interactions in a hadron resonance gas

“…The small value of r p in the 1b scheme leads to negligible effects on the fit of the hadron yields, and indeed in this case the results are very close to the I -HRG ones. In the 2b scheme there is a notable improvement, which is related to the different EV interactions for strange and non-strange hadrons with the introduction of an additional free parameter r Λ for all strange particles; here we have the non trivial result of smaller strange states with respect to light ones with equal mass (r Λ < r p ), which is compatible with what is found from fits to lattice QCD [19]. With respect to the 2b scheme, the 4b one introduces a meson-baryon difference with 4 free parameters: r π , r K , r p , and r Λ ; this leads to an even more essential improvement of the quality of the fit.…”

“…(8) is assumed for all hadrons, with a common α parameter. Note that the same schemes have already been studied for pure gauge theories [38] and lattice QCD simulations [19].…”

“…In the present paper we discuss the fit of mean hadron multiplicities and the role of EV effects. In [19] has been performed a systematic study of the same EV schemes here presented together with a modified hadronic list with undetected higher-mass resonances, and it has been shown how their combined effect leads to a consistent description of lattice QCD thermodynamics and experimental measurements of hadronic yields.…”

“…We employ the EV-HRG model (3)-(5) to describe experimental data on particle yields at mid-rapidity for π ± , K ± , p(p) [23], K 0 S , Λ [24], Ξ ∓ , Ω +Ω [25,26] and φ [27] in Pb+Pb collisions at Data Group [28]; we employ here the list called PDG2014 in Ref. [19]. For more details on the implementation of the model see [11,29,30].…”

“…Table 1 lists the results of the fits with different EV schemes. In the 1b and 2b schemes the proton radius r p is not included in the fitting procedure, but rather fixed to the values obtained from the fit to lattice QCD thermodynamics with the same hadron list [19]. This is done to avoid the instability of thermal fits for experimental data in these schemes, related to the appearance of the "second minimum" structure in the χ 2 as a function of T which manifests at very high temperatures [22,34]; it should be noted that the second minimum generally corresponds to very large values of the packing factor, stressing the condition of a dilute system where the EV-HRG model is more reliable.…”