Measurements and interpretations of W+-Z production cross-sections in pp collisions at SQUARE ROOTs = 13 TeV with the ATLAS detector

Abstract

Measurements of integrated and differential cross-sections for W+-Z production in proton-proton collisions are presented. The data collected by the ATLAS detector at theLarge Hadron Collider from 2015 to 2018 at a centre-of-mass energy of SQUARE ROOTs = 13TeV areused, corresponding to an integrated luminosity of 140 fb-1. The W+-Z candidate events arereconstructed using leptonic decay modes of the gauge bosons into electrons or muons. Theintegrated cross-section per lepton flavour for the production of W+-Z is measured in thedetector fiducial region with a relative precision of 4%. The measured value is compared withthe Standard Model prediction at a precision of up to next-to-next-to-leading-order in QCDand next-to-leading-order in electroweak. Cross-sections for W+Z and W-Z production andtheir ratio are presented. The W+-Z production is also measured differentially as functions ofvarious kinematic variables, including new observables sensitive to CP-violation effects. Allmeasurements are compared with state-of-the-art Standard Model predictions from fixedordercalculations or Monte Carlo generators based on next-to-leading-order matrix elementsinterfaced with parton showers. An effective field theory interpretation of the measurements isperformed, considering both CP-conserving and CP-violating dimension-6 operators modifyingthe W+-Z production. In the absence of observed deviations from the Standard Model, limitson CP-conserving Wilson coefficients are extracted using the transverse mass of the W+-Zsystem. For CP-violating coefficients a machine learning approach is used to construct an observable with enhanced sensitivity to CP-violation effects.