Abstract
This Letter presents the first study of the energy-dependence of diboson polarization fractions in WZ→ℓνℓ′ℓ′ (ℓ,ℓ′=e,μ) production. The data set used corresponds to an integrated luminosity of 140 fb−1 of proton-proton collisions at a center-of-mass energy of 13 TeV recorded by the ATLAS detector. Two fiducial regions with an enhanced presence of events featuring two longitudinally-polarized bosons are defined. A non-zero fraction of events with two longitudinally-polarized bosons is measured with an observed significance of 5.3 standard deviations in the region with 100<pZT≤200 GeV and 1.6 standard deviations in the region with pZT>200 GeV, where pZT is the transverse momentum of the Z boson. This Letter also reports the first study of the Radiation Amplitude Zero effect. Events with two transversely-polarized bosons are analyzed for the ΔY(ℓWZ) and ΔY(WZ) distributions defined respectively as the rapidity difference between the lepton from the W boson decay and the Z boson and the rapidity difference between the W boson and the Z boson. Significant suppression of events near zero is observed in both distributions. Unfolded ΔY(ℓWZ) and ΔY(WZ) distributions are also measured and compared to theoretical predictions.
