${\mathbf{Z}}(\nu \bar {\nu })\gamma$Measurement and Neutral aTGC Limits at 13 TeV with the ATLAS Detector

Abstract

The production of a Z boson in association with a high-energy photon (γ) in proton-proton collisions has been studied at the Large Hadron Collider (LHC). These studies have been used to test the electroweak sector of the Standard Model and to search for new physics effects, such as potential couplings of Z bosons to photons. The Zγ production with the Z boson decaying into neutrinos has been measured with data collected by the ATLAS detector during the 2015–2016 period at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 36.1 fb^–1. Candidate Zγ events with invisible decays of the Z boson are selected by requiring significant transverse momentum $({{p}_{T}})$ of the neutrinos system in conjunction with a single isolated photon with large transverse energy (E_T). Evidence of anomalous triple gauge-boson couplings is sought in Zγ production with photon E_T greater than 600 GeV. No excess is observed relative to the Standard Model expectation, and upper limits are set on the strength of ZZγ and Zγγ couplings.