Measurement of jet radial profiles in Pb–Pb collisions at sNN=2.76 TeV

Abstract The jet radial structure and particle transverse momentum ( p T ) composition within jets are presented in centrality-selected Pb–Pb collisions at s NN = 2.76 TeV. Track-based jets, which are also called charged jets, were reconstructed with a resolution parameter of R = 0.3 at midrapidity | η ch jet | 0.6 for transverse momenta p T , ch jet = 30 –120 GeV/ c . Jet–hadron correlations in relative azimuth and pseudorapidity space (Δ φ , Δ η ) are measured to study the distribution of the associated particles around the jet axis for different p T , assoc -ranges between 1 and 20 GeV/ c . The data in Pb–Pb collisions are compared to reference distributions for pp collisions, obtained using embedded PYTHIA simulations. The number of high- p T associate particles ( 4 p T , assoc 20 GeV/ c ) in Pb–Pb collisions is found to be suppressed compared to the reference by 30 to 10%, depending on centrality. associate particles ( 1 p T , assoc 3 GeV/ c ) tend to be enhanced in Pb–Pb collisions. The radial particle distribution relative to the jet axis shows a moderate modification in Pb–Pb collisions with respect to PYTHIA. High- p T associate particles are slightly more collimated in Pb–Pb collisions compared to the reference, while low- p T associate particle tend to be broadened. The results, which are presented for the first time down to p T , ch jet = 30 GeV/ c in Pb–Pb collisions, are compatible with both previous jet–hadron-related measurements from the CMS Collaboration and jet shape measurements from the ALICE Collaboration at higher p T , and add further support for the established picture of in-medium parton energy loss.