Mapping the redistribution of jet energy in PbPb collisions at the LHC with CMS

Abstract

Quenched jets produced in heavy ion collisions at the LHC and reconstructed with the CMS detector are studied to understand the nature of interactions between hardscattered partons and the simultaneously produced hot and dense medium, the Quark- Gluon Plasma (QGP). Jets are objects with color charge evolving through many energy scales, so are an excellent tool for scattering experiment in QGP, with potential to resolve quasiparticle structure and induce medium response. Redistribution of jet energy is quantified in two methods: measurement of transverse PT of final state particles projected onto dijet azimuthal axis, and measurement of jet production cross sections in PbPb and pp as function of jet radius. Missing momentum shows recovery of lost energy when moving beyond the jet cone for a fixed collection of jets, approaching full recovery at ... A jet radius scan of jet production cross sections shows consistent observed suppression in PbPb when compared to appropriately scaled pp at all radii. However, less suppression is observed with increasing jet resolution parameter R. In combination the results imply that while jet energy lost to medium interactions can be found when looking beyond the jet cone, the substantial changes to the jet population in pp at each studied R lead to sustained spectral suppression with even the largest cone size.