Study of jet quenching with Z+jet correlations in PbPb and $pp$ collisions at $\sqrt{s}_{NN}$ = 5.02 TeV

Abstract

The production of jets in association with Z bosons, reconstructed via the $\mu^{+}\mu^{-}$ and $e^{+}e^-$ decay channels, is studied in pp 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 pp and Pb-Pb collisions for Z bosons with transverse momentum $p_{T}^{Z} >$ 60 GeV/c and a recoiling jet with $p_{T}^{jet} >$ 30 GeV/c. The $p_T$ imbalance $x_{jZ} = p_{T}^{jet}/p_{T}^Z$, as well as the average number of jet partners per Z, $R_{jZ}$, was studied in intervals of pTZ. The RjZ is found to be smaller in Pb-Pb than in pp collisions, which suggests that in Pb-Pb collisions a larger fraction of partons associated with the Z bosons fall below the 30 GeV/c $p_{T}^{jet}$ threshold because they lose energy.Physical review letters 119(8), 082301(2017). doi:10.1103/PhysRevLett.119.082301Published by APS, College Park, Md.