Abstract

The production of jets in association with Z bosons, reconstructed via the μ^{+}μ^{-} 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 5.02TeV. 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 p_{T}^{Z}. The R_{jZ} 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.

Highlights

  • The correlated production of vector bosons and jets in hard parton scatterings occurring in ultrarelativistic heavy ion collisions provides an ideal probe of the quark-gluon plasma (QGP), a deconfined state of quarks and gluons [1,2]

  • This Letter describes the identification of Z þ jet pairs in pp and Pb-Pb collisions, and the first characterization of parton energy loss through angular and pT correlations between the jet and the Z, reconstructed in dimuon or dielectron decays

  • Within the solenoid volume are a silicon pixel and strip tracker, a lead tungstate crystal electromagnetic calorimeter (ECAL), and a brass and scintillator hadron calorimeter (HCAL), each composed of a barrel and two end cap sections

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Summary

Introduction

The correlated production of vector bosons and jets in hard parton scatterings occurring in ultrarelativistic heavy ion collisions provides an ideal probe of the quark-gluon plasma (QGP), a deconfined state of quarks and gluons [1,2]. Given the coarse centrality range used in the analysis, the difference between the measured and simulated Pb-Pb events has a negligible effect on jet reconstruction. Simulation studies show that the jet selection efficiency and the energy resolution are well understood for this kinematic range.

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