Jet fragmentation functions in PbPb and pp collisions at 2.76 TeV with CMS

The jet fragmentation function of inclusive jets with $p_T > 100$ GeV/c in PbPb collisions is measured for reconstructed charged particles with $p_T> 1$ GeV/c within the jet cone. A data sample of PbPb collisions collected in 2011 at a nucleon-nucleon center-of-mass energy of 2.76 TeV corresponding to an integrated luminosity of 129 inverse microbarn is used. The results for PbPb collisions as a function of collision centrality are compared to reference distributions based on pp data collected at the same collision energy. A centrality-ordered modification of the fragmentation function is revealed. For the most central collisions a significant rise of the PbPb/pp fragmentation function ratio for the softest fragmentation products with $p_T< 3$ GeV/c is observed.