Abstract
We report results on jet production in Pb–Pb collisions at √sNN = 2.76 TeV from the ALICE collaboration. The nuclear modification factor of jets reconstructed with a resolution parameter R=0.2 shows a strong, centrality dependent suppression with respect to pp collisions. The azimuthal anisotropy of charged jet production relative to the event plane is studied. In semi-peripheral events, a significant υ 2 ch jet is observed, indicating path-length dependent in-medium parton energy loss. The measurement of jet shapes allows characterizing the intra-jet momentum flow of quenched jets. The measured radial moment and dispersion of the constituent transverse momentum distribution indicate a collimation and hardening of the jet core in Pb–Pb relative to pp collisions.
Highlights
Jets are collimated sprays of particles associated with hard-scattered partons
The nuclear modification factor of jets reconstructed with a resolution parameter R=0.2 shows a strong, centrality dependent suppression with respect to pp collisions
The observed value of the jet nuclear modification factor is similar to the RAA of charged hadrons [15], which indicates that a significant fraction of the lost parton energy is not recovered inside the jet cone
Summary
Jets are collimated sprays of particles associated with hard-scattered partons. The study of jet production and fragmentation allows us to test our understanding of perturbative and non-perturbative aspects of QCD. Interactions with the medium result in collisional energy loss and give rise to additional induced radiation, which emitted at small angles inside the jet cone can lead to a broadening of the jet profile. Measurements of the jet shape characterize the intra-jet momentum flow, and help to distinguish between a possible jet collimation or broadening as a consequence of jet quenching. The path-length dependence of parton energy loss is sensitive to the underlying energy-loss mechanism. The amount of lost energy depends linearly on the path-length, while for radiative energy loss [1], the dependence is quadratic due to interference effects. The dependence can be studied by measuring jet production relative to the orientation of the event plane, defined via the symmetry axis of the initial nucleon distribution of the collision overlap region
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