Energy and system size dependence of chemical freeze-out in relativistic nuclear collisions

We present a detailed study of chemical freeze-out in p-p, C-C, Si-Si, and Pb-Pb collisions at beam momenta of 158A GeV as well as Pb-Pb collisions at beam momenta of 20A, 30A, 40A, and 80A GeV. By analyzing hadronic multiplicities within the statistical hadronization model, we studied the parameters of the source as a function of the number of participating nucleons and the beam energy. We observe a nice smooth behavior of temperature, baryon chemical potential, and strangeness under-saturation parameter as a function of energy and nucleus size. Interpolating formulas are provided which allow us to predict the chemical freeze-out parameters in central collisions at center-of-mass energies $\sqrt{s}{}_{\mathit{NN}}\ensuremath{\gtrsim}4.5$ GeV and for any colliding ions. Specific discrepancies between data and the model emerge in particle ratios in Pb-Pb collisions at beam energies between 20A and 40A GeV which cannot be accounted for in the considered model schemes.

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