Statistical model predictions for particle ratios at √sNN = 5.5 TeV

Particle production in central Pb-Pb collisions at LHC is discussed in the context of the Statistical Model. Predictions of various particle ratios are presented with the corresponding choice of model parameters made according to the systematics extracted from heavy-ion collisions at lower energies. The sensitivity of several ratios on the temperature and the baryon chemical potential is studied in detail, and some of them, which are particularly appropriate to determine the chemical freeze-out point experimentally, are indicated. We show that the ¯/p ratio is most suitable to determine the baryon chemical potential while the /K and /� ratios are best to determine the temperature at chemical freeze-out. Particle production observed in heavy-ion collisions al- lows a systematic study of the thermal properties of the final state. In a wide energy range, from the SIS up to RHIC, the yields of produced particles have been shown to be consistent with the assumption that hadrons origi- nate from a thermal source with a given temperature and a given baryon density. These properties have been quan- tified by comparing the measured particle ratios with Statistical Model calculations. By using only two ther- mal parameters, a successful description of particle ratios measured in heavy-ion collisions over a wide range of cen- ter of mass energies could be made (1). The extracted chemical freeze-out parameters, the temperature T and the baryon chemical potential µB can be characterized by a constant average energy per hadron h Ei /h N i of ap- proximately 1 GeV (2). The extrapolation of this freeze- out curve towards vanishing µB is bounded by the criti- cal phase transition temperature as calculated in Lattice Gauge Theory (3). In view of the success of the Statistical Model, we dis- cuss in this paper the expectations for particle ratios in central heavy-ion collisions at the LHC energy. The cal- culations are performed at the chemical decoupling point extrapolated from the freeze-out systematics. The parti- cle ratios are discussed with respect to their sensitivity to variations in the thermal parameters. Based on this anal- ysis, we suggest observables which are best suited to ex- tract experimentally the freeze-out conditions in heavy- ion collisions at the LHC energy. At LHC energies, due to the large number of pro- duced particles, a novel type of data analysis will be possible. In particular, the thermal origin and chemi- cal decoupling conditions in heavy-ion collisions can be studied for various event classes and even within a sin- gle event. Consequently, the freeze-out conditions can be extracted event-wise, leading to distributions of the temperature and baryon chemical potential determined event-wise. Instead of a full analysis within the Statisti- cal Model, the proposed particle ratios can be utilized to extract these values. Furthermore, at these energies most particles might be produced via hard collisions which could lead to particle ratios substantially different from those of the Statistical Model. Deviations from these predictions might lead to new insight into the hadronisation mechanism.