Study of $WWγ$ and $WZγ$ production in $pp$ collisions at $\sqrt{s} = 8$ TeV and search for anomalous quartic gauge couplings with the ATLAS experiment

Abstract

This paper presents a study of $WWγ$ and $WZγ$ triboson production using events from proton--proton collisions at a centre-of-mass energy of $\sqrt{s} = 8$ TeV recorded with the ATLAS detector at the LHC and corresponding to an integrated luminosity of 20.2 fb$^{-1}$. The $WWγ$ production cross-section is determined using a final state containing an electron, a muon, a photon, and neutrinos ($eνμνγ$). Upper limits on the production cross-section of the $eνμνγ$ final state and the $WWγ$ and $WZγ$ final states containing an electron or a muon, two jets, a photon, and a neutrino ($eνjjγ$ or $μνjjγ$) are also derived. The results are compared to the cross-sections predicted by the Standard Model at next-to-leading order in the strong-coupling constant. In addition, upper limits on the production cross-sections are derived in a fiducial region optimised for a search for new physics beyond the Standard Model. The results are interpreted in the context of anomalous quartic gauge couplings using an effective field theory. Confidence intervals at 95% confidence level are derived for the 14 coupling coefficients to which $WWγ$ and $WZγ$ production are sensitive.