Observation of Z production in proton-lead collisions at LHCb

Abstract

The first observation of Z boson production in proton-lead collisions at a centre-of-mass energy per proton-nucleon pair of sNN−−−−√

= 5 TeV is presented. The data sample corresponds to an integrated luminosity of 1.6 nb−1 collected with the LHCb detector. The Z candidates are reconstructed from pairs of oppositely charged muons with pseudorapidities between 2.0 and 4.5 and transverse momenta above 20 GeV/c. The invariant dimuon mass is restricted to the range 60 − 120 GeV/c. The Z production cross-section is measured to be σZ→μ+μ−(fwd)=13.5+5.4−4.0(stat.)±1.2(syst.)nb

in the direction of the proton beam and σZ→μ+μ−(bwd)=10.7+8.4−5.1(stat.)±1.0(syst.)nb

in the direction of the lead beam, where the first uncertainty is statistical and the second systematic.