Understanding partonic energy loss from measured light charged particles and jets in PbPb collisions at LHC energies

Abstract

We perform a comprehensive study of partonic energy loss reflected in the nuclear modification factors of charged particles and jets measured in PbPb collisions at √ sNN = 2.76 and 5.02 TeV in wide transverse momentum (pT) and centrality range. The pT distributions in pp collisions are fitted with a modified power law and the nuclear modification factor in PbPb collisions can be obtained using effective shift (∆pT) in the spectrum measured at different centralities. Driven by physics consideration, the functional form of energy loss given by ∆pT can be assumed as power law with different power indices in three different pT regions. The power indices and the boundaries of three pT regions are obtained by fitting the measured nuclear modification factor as a function of pT in all collision centralities simultaneously. The energy loss in different collisions centralities are described in terms of fractional power of number of participants. It is demanded that the power law functions in three pT regions and their derivatives are continuous at the pT boundaries. The ∆pT for light charged particles is found to increase linearly with pT in low pT region below ∼ 5−6 GeV/c and approaches a constant value in high pT region above ∼ 22− 29 GeV/c with an intermediate power law connecting the two regions. The method is also used for jets and it is found that for jets, the ∆pT increases approximately linearly even at very high pT. ar X iv :2 10 5. 06 36 4v 1 [ he pph ] 1 3 M ay 2 02 1 Understanding partonic energy loss ... 2