Study of W boson production in PbPb and pp collisions at sqrt(s[NN]) = 2.76 TeV

TL;DR

This paper reports the measurement of W boson production in lead-lead and proton-proton collisions at 2.76 TeV, confirming that yields scale with the number of nucleon-nucleon collisions and agree with theoretical predictions.

Contribution

First measurement of W boson production in PbPb collisions at the LHC, showing consistency with scaled pp results and perturbative QCD calculations.

Findings

W boson yields scale with the number of NN collisions in PbPb

W yields in PbPb and pp are consistent after accounting for nuclear content

Results agree with next-to-leading order perturbative QCD predictions

Abstract

A measurement is presented of W-boson production in PbPb collisions carried out at a nucleon-nucleon (NN) centre-of-mass energy sqrt(s[NN]) of 2.76 TeV at the LHC using the CMS detector. In data corresponding to an integrated luminosity of 7.3 inverse microbarns, the number of W to mu mu-neutrino decays is extracted in the region of muon pseudorapidity abs(eta[mu])<2.1 and transverse momentum pt[mu]>25 GeV. Yields of muons found per unit of pseudorapidity correspond to (159 +/- 10 (stat.) +/- 12 (syst.)) 10E-8 W(plus) and (154 +/- 10 (stat.) +/- 12 (syst.)) 10E-8 W(minus) bosons per minimum-bias PbPb collision. The dependence of W production on the centrality of PbPb collisions is consistent with a scaling of the yield by the number of incoherent NN collisions. The yield of W bosons is also studied in a sample of pp interactions at sqrt(s)= 2.76 TeV corresponding to an integrated luminosity of 231 inverse nanobarns. The individual W(plus) and W(minus) yields in PbPb and pp collisions are found to agree, once the neutron and proton content in Pb nuclei is taken into account. Likewise, the difference observed in the dependence of the positive and negative muon production on pseudorapidity is consistent with next-to-leading order perturbative QCD calculations.