Measurement of the charged-hadron spectra and nuclear modification factor in lead–lead collisions with the ATLAS detector

Abstract

The ATLAS experiment at the Large Hadron Collider (LHC) measures charged hadron spectra obtained in 2010 and 2011 lead-lead LHC data taking periods with total integrated statistics of 0.15 nb −1 . The results are compared to the pp spectra of charged hadrons at the same centre-of-mass energy based on the data sample with integrated luminosity of 4.2 pb −1 obtained by the ATLAS experiment in 2011 and 2013. This allows a detailed comparison of the two collision systems in a wide transverse momentum (0.5 < pT < 150 GeV) and pseudorapidity (|η| < 2) ranges in different centrality intervals of Pb+Pb collision. The nuclear modification factor RAA is presented in detail as a function of centrality, pT and η. It shows a distinct pT-dependence with a pronounced minimum at about 7 GeV. Above 60 GeV, it is consistent with a flat, centrality-dependent, value within the uncertainties. The value is 0.55 ± 0.01(stat.) ± 0.04(syst.) in the most central collisions. The RAA is observed to be consistent with flat |η| dependence over the whole transverse momentum range in all centrality classes.