Surprisingly large uncertainties in temperature extraction from thermal fits to hadron yield data at LHC

Understand

The conventional hadron-resonance gas (HRG) model with the Particle Data Group (PDG) hadron input, full chemical equilibrium, and the hadron type dependent eigenvolume interactions is employed to fit the hadron mid-rapidity yield data of ALICE Collaboration for the most central Pb+Pb collisions.

• For the case of point-like hadrons the well-known fit result $T = 154 \pm 2$ MeV is reproduced.
• However, the situation changes if hadrons have different eigenvolumes.
• In the case when all mesons are point-like while all baryons have an effective hard-core radius of 0.3 fm the $\chi^2$ temperature dependence of the $\chi^2$ has a broad minimum in the temperature range of $155-210$ MeV, with fit quality comparable to the $T \sim 155$ MeV minimum in the point-particle case.