  Presented are the results of a detailed study for a complete simulation of
the CMS detectors at the LHC in view of the expected modification of jet
fragmentation functions in central Pb+Pb collisions at (s_NN)**0.5=5.5 TeV
compared to the vacuum (p+p) case. The study is based on photon-jet events,
using the correlation between isolated high-transverse energy (E_T>70 GeV)
photons and fully reconstructed jets, based on the information provided by the
CMS calorimeters and silicon tracker.
