Measurement of jet fragmentation in PbPb and pp collisions at root s(NN)=2.76 TeV

The jet fragmentation functionof inclusive jets with transverse momentum p_T above 100GeV/c in PbPb collisionshas been measured using reconstructed charged particleswith p_T above 1GeV/c in a cone of radius 0.3 around the jet axis. A data sample of PbPb collisionscollected in 2011 at a nucleon-nucleon center-of- massenergy of √sNN = 2.76 TeV corresponding to an integrated luminosity of 150μb^(−1) is used. The results for PbPb collisionsas a function of collisioncentrality and jet transverse momentum are compared to reference distributions based on pp data collected at the same center-of- massenergy in 2013, with an integrated luminosity of 5.3pb^(−1). A centrality-dependent modification of the fragmentation functionis found. For the most central collisions, a significant enhancement is observed in the PbPb/pp fragmentation functionratio for charged particleswith p_T less than 3GeV/c. This enhancement is observed for all jet p_T bins studied.