Study of jet quenching using di-jet and photon-jet events in PbPb collisions at 2.76 TeV with CMS

Abstract

The first measurement of the transverse momentum imbalance of isolated-photon-jet pairs and the modification of fragmentation function of the inclusive jets in relativistic heavy ion collisions are reported. The analysis uses data from PbPb collisions at a center-of-mass energy of 2.76 TeV per nucleon pair and corresponding to an integrated luminosity of 150 μb−1 recorded by the CMS experiment at the LHC in 2011. For events containing an isolated photon with transverse momentum pT > 60 GeV/c and an associated jet with pT > 30 GeV/c, the photon-jet pT imbalance is studied as a function of collision centrality and compared to pp data and PYTHIA calculations at the same center-of-mass energy. Using the pT of the isolated photon as an estimate of the energy of the associated parton at production, this measurement allows an unbiased characterization of the in-medium parton energy loss. In addition, further study on the modification of jet fragmentation function was studied using inclusive jets with pT > 100 GeV/c. Both show the gradual centrality dependence of jet energy loss and fragmentation function modification.