Finite resonance widths influence the thermal-model description of hadron yields

摘要

Different scenarios for modeling resonances in a thermal model description of hadron yields measured in heavy-ion collisions are explored: the zero-width approximation, the energy-independent Breit-Wigner scheme, and the energy-dependent Breit-Wigner (eBW) scheme. Application of the eBW scheme leads to a notable suppression in the proton yields, stemming mainly from a reduced feed-down from Delta resonances because of the threshold effects. A significantly improved agreement of a thermal model with hadron yields measured in Pb-Pb collisions at root s(NN) = 2.76 TeV by the ALICE Collaboration is obtained in the eBW scheme at T similar or equal to 155 MeV, indicating a possible resolution of the so-called "proton anomaly." The results obtained show that there are significant systematic uncertainties in the thermal model due to the modeling of broad resonances.