Centrality dependence of PT distributions and nuclear modification factor of charged particles in Pb–Pb interactions at SNN=2.76 TeV

Abstract

The simulation of transverse momentum (PT) spectra of inclusive charged hadrons computed with absolute pseudorapidity below 0.8 (|η|<0.8)in different centrality bins in Pb−Pbinteractions at SNN=2.76TeVare reported. The results obtained from Monte Carlo models including QGSJETII-03, QGSJET-04, EPOS1.99, and EPOS-LHC are compared with the ALICE experimental data in the PTrange 0.15<PT<50GeV/c, for total of nine centrality classes from (0-5%) to (70-80%). The EPOS-LHC model reproduced the PTspectra in all the centrality classes except at 20-30 and 30-40% where the model underestimated the data at high PTonly. The QGSJET models overestimated the data over the entire PTrange and in all the centrality classes up to about 10%. Fit with the Tsallis–Pareto-like function of the pTspectra shows that the effective temperature depends on the centrality which increases from central to peripheral collisions as in the case of central collisions the fireball is longer lived as compared to the peripheral one. The Pb−Pbspectra are further oriented on the scale of the nuclear modification factor RAAusing a P−Pcollision spectrum calculated for the same center of mass energy. Although the models could not reproduce the data but showed similar behavior only, that shows that particle suppression has a significant effect on the centrality at high PT. The suppression is maximum in the most central collisions above which there is a remarkable escalation in the nuclear modification factor. In the case of most peripheral interactions, the suppression is smaller as compared to the most central one and is nearly independent of PT. The EPOS model’s calculation exhibit suppression for all class intervals, having the robust effect for the most central interval (0-5%) due to the relative parton energy loss and reveals a least repression effect in most peripheral cases (70-80%). Results of the QGSJETII models are not included for the RAAas the models failed to predict the data. The reason is that QGSJETII is not a Glauber–based model but a model based on soft pomeron dynamics. The model does not provide the number of binary sub-collisions we need to scale down the RAA.

Keywords

• Heavy-ion interactions
• Nuclear modification factor
• Monte Carlo models