Study of Z production in PbPb and pp collisions at sqrt(s[NN]) = 2.76 TeV in the dimuon and dielectron decay channels

TL;DR

This study measures Z boson production in PbPb and pp collisions at 2.76 TeV using CMS data, confirming binary collision scaling and providing insights into the medium's effect on Z boson yields.

Contribution

First measurement of Z boson yields in PbPb and pp collisions at 2.76 TeV across multiple decay channels, confirming binary scaling in heavy ion collisions.

Findings

PbPb to pp yield ratio ~1.04, consistent with binary scaling

Z boson yields unaffected by the hot dense medium

Results support Z bosons as a standard candle in heavy ion physics

Abstract

The production of Z bosons is studied in the dimuon and dielectron decay channels in PbPb and pp collisions at sqrt(s[NN]) = 2.76 TeV, using data collected by the CMS experiment at the LHC. The PbPb data sample corresponds to an integrated luminosity of about 150 inverse microbarns, while the pp data sample collected in 2013 at the same nucleon-nucleon centre-of-mass energy has an integrated luminosity of 5.4 inverse picobarns. The Z boson yield is measured as a function of rapidity, transverse momentum, and collision centrality. The ratio of PbPb to pp yields, scaled by the number of inelastic nucleon-nucleon collisions, is found to be 1.06 +/- 0.05 (stat) +/- 0.08 (syst) in the dimuon channel and 1.02 +/- 0.08 (stat) +/- 0.15 (syst) in the dielectron channel, for centrality-integrated Z boson production. This binary collision scaling is seen to hold in the entire kinematic region studied, as expected for a colourless probe that is unaffected by the hot and dense QCD medium produced in heavy ion collisions.