Surprisingly large uncertainties in temperature extraction from thermal fits to hadron yield data at LHC
Year: 2017
Type: article
Abstract: The conventional hadron-resonance gas (HRG) model with the Particle Data Group hadron input, full chemical equilibrium, and the hadron-type dependent eigenvolume interactions, is employed to fit the hadron midrapidity yield data of the ALICE collaboration for the most central Pb+Pb collisions. For the case of point-like hadrons, the well-known fit result T = 154 ± 2 MeV is reproduced. However, the situation changes if the hadrons have different eigenvolumes. In the case when all the mesons are point-like while all the baryons have an effective hardcore radius of 0.3 fm, the temperature dependence of χ 2 has a broad minimum in the temperature range of 155−210 MeV, with a fit quality comparable to the T ∼ 155 MeV minimum in the point-particle case. A very similar result is obtained when only baryon–baryon eigenvolume interactions are considered, with the eigenvolume parameter taken from the previous fit to the ground state of nuclear matter. Finally, when we apply the eigenvolume corrections with a mass-proportional eigenvolume v i ∼ m i , fixed to a particular hardcore proton radius r p , we observe a second minimum in the temperature dependence of χ 2 , located at significantly higher temperatures. For instance, at r p = 0.5 fm, the fit quality is better than in the point-particle HRG case in a very wide temperature range of 170−320 MeV, which creates uncertainty in the temperature determination from the fit to the data of 150 MeV. These results show that thermal fits to the heavy-ion hadron yield data are very sensitive to the modeling of the short-range repulsion eigenvolume between hadrons, and that the chemical freeze-out temperature can only be extracted from the LHC hadron yield data with sizable uncertainty.
Authors: Volodymyr Vovchenko, Horst Stoecker
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W2586544959