Evidence for Longitudinally Polarized W Bosons in the Electroweak Production of Same-Sign W Boson Pairs in Association with Two Jets in pp Collisions at SQUARE ROOTs = 13 TeV with the ATLAS Detector

Abstract

This Letter reports the first evidence of electroweak production of same-signW boson pairs where at leastone of theW bosons is longitudinally polarized and the most stringent constraint to date for the production oftwo longitudinally polarized same-sign W bosons. The dataset used corresponds to an integrated luminosityof 140 fb-1 of proton-proton collisions at a center-of-mass energy of 13 TeV, collected with the ATLASdetector during run 2 of the Large Hadron Collider. The study is performed in final states including twosame-sign leptons (electrons or muons), missing transverse momentum, and at least two jets with a largeinvariant mass and a large rapidity difference. Two independent fits are performed targeting the productionof same-signW bosons with at least one, or two longitudinally polarizedW bosons. The observed (expected)significance of the production with at least one longitudinally polarized W boson is 3.3 (4.0) standarddeviations. An observed (expected) 95% confidence level upper limit of 0.45 (0.70) fb is reported on thefiducial production cross section of two longitudinally polarized same-sign W bosons.