Modification of jet shapes in PbPb collisions at sqrt(sNN)=2.76 TeV

The first measurement of jet shapes, defined as the fractional transverse momentum radial distribution, for inclusive jets produced in heavy-ion collisions is presented. Data samples of PbPb and pp collisions, corresponding to integrated luminosities of 150 ?b-1 and 5.3 pb-1 respectively, were collected at a nucleon-nucleon centre-of-mass energy of sNN=2.76TeV with the CMS detector at the LHC. The jets are reconstructed with the anti-kT algorithm with a distance parameter R = 0.3, and the jet shapes are measured for charged particles with transverse momentum pT > 1GeV/c. The jet shapes measured in PbPb collisions in different collision centralities are compared to reference distributions based on the pp data. A centrality-dependent modification of the jet shapes is observed in the more central PbPb collisions, indicating a redistribution of the energy inside the jet cone. This measurement provides information about the parton shower mechanism in the hot and dense medium produced in heavy-ion collisions.