2026/07/22 by ATLAS Collaboration
#hep-ex
Measurements of polarisation states of W and Z gauge bosons in electroweak W±Z production in association with two jets (WZjj-EW) in proton-proton collisions are presented. The data set used corresponds to integrated luminosities of 140 fb-1 and 164 fb-1 of proton-proton collisions at centre-of-mass energies of 13 TeV and 13.6 TeV, respectively, recorded by the ATLAS detector at the CERN Large Hadron Collider. The W±Z candidate events are reconstructed using leptonic decay modes of the gauge bosons into electrons and muons. The observed significance for the presence in data of WZjj-EW events containing a longitudinally polarised Z boson is of 4.0 standard deviations. The measured fraction of such events, integrated over the fiducial region, is fX0 = 0.32 ± 0.09, in agreement with the Standard Model prediction at next-to-leading-order in electroweak corrections. Upper limits at 95% confidence level of 0.19 and 0.12 are set on the fraction of events with a W boson longitudinally polarised and on the fraction of events with the two bosons longitudinally polarised, respectively. The integrated fiducial cross-section per lepton flavour of WZjj-EW production at √(s) = 13.6 TeV is also measured to be σWZjj-EW → ℓ' νℓ ℓ jj = 0.374 ± 0.077 (stat.) ± 0.053 (syst.) ± 0.009 (lumi.) fb, where ℓ and ℓ' are either an electron or a muon. This measurement is in agreement with the Standard Model expectation.