Impact of resonance regeneration and decay on the net proton fluctuations in a hadron resonance gas

Abstract

We investigate net-proton fluctuations as important observables measured in heavy-ion collisions within the hadron resonance gas (HRG) model. Special emphasis is given to effects which are a priori not inherent in a thermally and chemically equilibrated HRG approach. In particular, we point out the importance of taking into account the successive regeneration and decay of resonances after the chemical freeze-out, which lead to a randomization of the isospin of nucleons and thus to additional fluctuations in the net-proton number. We find good agreement between our model results and the recent STAR measurements of the higher-order moments of the net-proton distribution.

Impact of resonance decays on critical point signals in net-proton fluctuations

“…Resonance decays contribute significantly to the final state particle multiplicities and, consequently, to event-byevent multiplicity distributions. Their impact on net-proton number fluctuations, ignoring the possible presence of a critical point, was previously studied in [30,31]. It was found that the decay processes do not significantly modify the primordial (without resonance decays) ratios of net-proton number cumulants if the probabilistic decay contributions are properly taken into account [31].…”

“…Their impact on net-proton number fluctuations, ignoring the possible presence of a critical point, was previously studied in [30,31]. It was found that the decay processes do not significantly modify the primordial (without resonance decays) ratios of net-proton number cumulants if the probabilistic decay contributions are properly taken into account [31]. This is because a thermal distribution of particles is being folded with a binomial decay distribution yielding again a nearly thermal distribution.…”

Lattice QCD results on chemical freeze-out

“…However, taking into account the effects of resonance feed-down and isospin randomization [36,37], one can show that the net-proton and net-baryon number fluctuations are numerically very similar, at least in the case of low-order fluctuations [38].…”

Higher moments of multiplicity fluctuations in a hadron-resonance gas with exact conservation laws

“…To calculate the resonance decay contributions to kurtosis in the CE include four nested loops over all particles and resonances, which is again fairly computing time consuming. In recent studies [21,22], the resonance decay contributions have been divided into an average and a probabilistic part. For example, in Eq.…”

“…Most calculations [17][18][19][20][21][22][23] on higher moments of multiplicity fluctuations in the HRG model employed only the GCE treatment. To approximately achieve conditions of the GCE, one is required to study fluctuations in a restricted phase space [24,25].…”