Comment on “Investigation of Hadron Multiplicity and Hadron Yield Ratios in Heavy-Ion Collisions”

Abstract

Oliinychenko, Bugaev and Sorin [arXiv:1204.0103 [hep-ph]] considered the role of conservation laws in discussing possible weaknesses of thermal models which are utilized in describing the hadron multiplicities measured in central nucleus-nucleus collisions. They argued to analyse the criteria for chemical freeze-out and to conclude that none of them were robust. Based on this, they suggested a new chemical freeze-out criterion. They assigned to the entropy per hadron the ad hoc value 7.18 and supposed to remain unchanged over the whole range of the baryo-chemical potentials. Due to unawareness of recent literature, the constant entropy per hadron has been discussed in Ref. [Fizika B18 (2009) 141-150, Europhys.Lett. 75 (2006 420]. Furthermore, it has been shown that the constant entropy per hadron is equivalent to constant entropy normalized to cubic temperature, an earlier criterion for the chemical freeze-out introduced in Ref. [Europhys.Lett. 75 (2006) 420, Nucl.Phys.A764 (2006 387-392]. In this comment, we list out the ignored literature, compare between the entropy-number density ratio and two criteria of averaged energy per averaged particle number and constant entropy per cubic temperature. All these criteria are confronted to the experimental results. The physics of constant entropy per number density is elaborated. It is concluded that this ratio can't remain constant, especially at large chemical potential related to AGS and SIS energies.

Possible interrelations among chemical freeze-out conditions

“…The agreement between the predicted values of s/n and extracted parameters is limited at small µ b . This suggests a limiting value of s/n around 7 at high temperature but when the temperature decreases the extracted parameters likely suggest smaller values, as s/n diverges at large µ b [26]. (a) Fig.…”

“…It was assumed that the entropy per particle can be utilized in describing the chemical freeze-out parameters [24][25][26]. The value of s/n was assumed as ∼ 7.…”

“…evidence for the adiabatic chemical hadron production in heavy-ion collisions [25,26]. The entropy per particle is also assumed to measure the average of the available microstates, i.e.…”

“…1but here for constant s/n. The solid line represents s/n = 7.18[25,26]. Left-hand panel (b) shows the dependence of s/n on temperature at different resonance spectrum masses.…”

An estimate of the thermodynamic pressure in high-energy collisions

“…In relating our estimate of the thermodynamic pressure to that deduced from lattice QCD simulations, the difficulty of performing lattice calculations at finite baryon chemical potential µ b should be taken into account. Assuming chemical freeze-out [45][46][47][48], the latter is to be related to the center-of-mass energy √ s.…”