Study of Jet Quenching with Z + jet Correlations in Pb-Pb and p p Collisions at √ s N N = 5.02 TeV

Abstract

The production of jets in association with Z bosons, reconstructed via the μ + μ − and e + e − decay channels, is studied in p p and, for the first time, in Pb-Pb collisions. Both data samples were collected by the CMS experiment at the LHC, at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The Pb-Pb collisions were analyzed in the 0%–30% centrality range. The back-to-back azimuthal alignment was studied in both p p and Pb-Pb collisions for Z bosons with transverse momentum p Z T > 60 GeV / c and a recoiling jet with p jet T > 30 GeV / c . The p T imbalance x j Z = p jet T / p Z T , as well as the average number of jet partners per Z , R j Z , was studied in intervals of p Z T . The R j Z is found to be smaller in Pb-Pb than in p p collisions, which suggests that in Pb-Pb collisions a larger fraction of partons associated with the Z bosons fall below the 30 GeV / c p jet T threshold because they lose energy.