Jet quenching in heavy-ion collisions with CMS

The energy loss of fast partons traversing the strongly interacting matter produced in relativistic heavy-ion collisions is one of the most interesting observables to probe the nature of the produced medium. The collisional and radiative energy loss of the partons will modify the fragmentation functions depending on the path length in the medium. In this report, we present a detailed study of complete simulated $\gamma$-jet events by the CMS detector at LHC in view of the expected modification of jet fragmentation functions in central collisions at $\sqrt{s_{NN}} = 5.5$ TeV compared to the p+p case. Since the produced prompt photon does not interact strongly with the medium, the initial transverse energy of the fragmentation parton can be related to the photon transverse energy in $\gamma$-jet events. This enables us to make precision measurements of the modification of the fragmentation function.