Interpreting single jet measurements in Pb+Pb collisions at the LHC

Abstract

Results are presented from a phenomenological analysis of recent measurements of jet suppression and modifications of jet fragmentation functions in Pb+Pb collisions at the LHC. Particular emphasis is placed on the impact of the differences between quark and gluon jet quenching on the transverse momentum (pjetT) dependence of the jet RAA and on the fragmentation functions, D(z). Primordial quark and gluon parton distributions were obtained from PYTHIA8 and were parameterized using simple power-law functions and extensions to the power-law function which were found to better describe the PYTHIA8 parton spectra. A simple model for the quark energy loss based on the shift formalism is used to model RAA and D(z) using both analytic results and using direct Monte-Carlo sampling of the PYTHIA parton spectra. The model is capable of describing the full pjetT, rapidity, and centrality dependence of the measured jet RAA using three effective parameters. A key result from the analysis is that the D(z) modifications observed in the data, excluding the enhancement at low-z, may result primarily from the different quenching of the quarks and gluons. The model is also capable of reproducing the charged hadron RAA at high transverse momentum. Predictions are made for the jet RAA at large rapidities where it has not yet been measured and for the rapidity dependence of D(z).