Abstract
This paper presents measurements of W^{pm }Z production cross sections in pp collisions at a centre-of-mass energy of 13 text {TeV}. The data were collected in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider, and correspond to an integrated luminosity of 36.1~hbox {fb}^{-1}. The W^{pm }Z candidate events are reconstructed using leptonic decay modes of the gauge bosons into electrons and muons. The measured inclusive cross section in the detector fiducial region for a single leptonic decay mode is sigma _{W^pm Z rightarrow ell ^{'} nu ell ell }^{text {fid.}} = 63.7 , pm ~1.0~text {(stat.)} , pm ~2.3~text {(syst.)} , pm ~1.4~text {(lumi.)} fb, reproduced by the next-to-next-to-leading-order Standard Model prediction of 61.5^{+1.4}_{-1.3} fb. Cross sections for W^+Z and W^-Z production and their ratio are presented as well as differential cross sections for several kinematic observables. An analysis of angular distributions of leptons from decays of W and Z bosons is performed for the first time in pair-produced events in hadronic collisions, and integrated helicity fractions in the detector fiducial region are measured for the W and Z bosons separately. Of particular interest, the longitudinal helicity fraction of pair-produced vector bosons is also measured.
Highlights
Background estimationThe background sources are classified into two groups: events where at least one of the candidate leptons is not a prompt lepton and events where all candidates are prompt leptons or are produced in the decay of a τ -lepton
The measurements of f0 and fL − fR are summarised in Table 5, where they are compared with the predictions from
The Powheg+Pythia Monte Carlo (MC) sample was generated at LO in the electroweak formalism using the Gμ scheme with sin2 θW = 0.2229
Summary
Measurements of W ± Z a centre-of-m√ass production at s energy of = 13 TeV were reported by the ATLAS [10] and CMS [11] collaborations using integrated luminosities of 3.2 fb−1 and 35.9 fb−1, respectively. Other W ± Z measurements in pp collisions, at centre-of-mass energies of 7 TeV and 8 TeV, were reported previously by ATLAS and CMS [12,13]. Polarisation and several other related angular coefficient measurements of a singly produced Z boson were published by the CDF [21], CMS [22] and ATLAS [23] collaborations. An analysis of angular distributions of leptons from decays of W and Z bosons is performed and integrated helicity fractions in the detector fiducial region are measured for the W and Z bosons separately
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