Measurement of W^± and Z-boson production cross sections in pp collisions at √s = 13 TeV with the ATLAS detector

Measurements of the W^±→ℓ^±ν and Z→ℓ⁺ℓ⁻ production cross sections (where ℓ^±=e^±,μ^±) in proton-proton collisions at √s=13 TeV are presented using data recorded by the ATLAS experiment at the Large Hadron Collider, corresponding to a total integrated luminosity of 81 pb⁻¹ The total inclusive W^±-boson production cross sections times the single-lepton-flavour branching ratios are σ^tot_W+=11.83±0.02(stat)±0.32(sys)±0.25(lumi) nb and σ^tot_W−=8.79±0.02(stat)±0.24(sys)±0.18(lumi) nb for W⁺ and W⁻, respectively. The total inclusive Z-boson production cross section times leptonic branching ratio, within the invariant mass window 66<m_ℓℓ<116 GeV, is σ^tot_Z=1.981±0.007(stat)±0.038(sys)±0.042(lumi) nb. The W⁺, W⁻, and Z-boson production cross sections and cross-section ratios within a fiducial region defined by the detector acceptance are also measured. The cross-section ratios benefit from significant cancellation of experimental uncertainties, resulting in σ^fid_W+/σ^fid_W−=1.295±0.003(stat)±0.010(sys) and σ^fid_W±/σ^fid_Z=10.31±0.04(stat)±0.20(sys). Theoretical predictions, based on calculations accurate to next-to-next-to-leading order for quantum chromodynamics and to next-to-leading order for electroweak processes and which employ different parton distribution function sets, are compared to these measurements.