Measurements ofZγandZγγproduction inppcollisions at<

Abstract

The production of Z bosons with one or two isolated high-energy photons is studied using pp collisions at ffiffi ffi s p ¼ 8 TeV. The analyses use a data sample with an integrated luminosity of 20.3 fb −1 collected by the ATLAS detector during the 2012 LHC data taking. The Zγ and Zγγ production cross sections are measured with leptonic (e þ e − , μ þ μ − , νν) decays of the Z boson, in extended fiducial regions defined in terms of the lepton and photon acceptance. They are then compared to cross-section predictions from the Standard Model, where the sources of the photons are radiation off initial-state quarks and radiative Z-boson decay to charged leptons, and from fragmentation of final-state quarks and gluons into photons. The yields of events with photon transverse energy E T > 250 GeV from l þ l − γ events and with E T > 400 GeV from ννγ events are used to search for anomalous triple gauge-boson couplings ZZγ and Zγγ. The yields of events with diphoton invariant mass m γγ > 200 GeV from l þ l − γγ events and with m γγ > 300 GeV from ννγγ events are used to search for anomalous quartic gauge-boson couplings ZZγγ and Zγγγ. No deviations from Standard Model predictions are observed and limits are placed on parameters used to describe anomalous triple and quartic gauge-boson couplings.

Zγ production in vector-boson scattering at next-to-leading order QCD

“…Current experimental constraints on these operators can be found in refs. [37,38]. Including anomalous gauge couplings, the amplitude rises as M(s) ∝ s 2 for large invariant masses s = m 2…”

Higgs phenomenology as a probe of sterile neutrinos

“…As they contain an electron and missing transverse energy, these events can easily populate the fiducial phase space of measurements aimed at W -bosons decaying to electrons and neutrinos [53], with the photon from the N decay also meaning that they can impact upon W + γ measurements [54]. They, and the neutral current Drell-Yan processes, can also contribute to inclusive photon and photon-plus-jet measurements [55,56], where no veto is made on the rest of the event, and photon-plus-missing-energy measurements [57]. The resultant exclusion is shown in Fig.…”

BSM constraints from model-independent measurements: A Contur Update

“…The measurements of interest are those involving isolated photons, or pairs of photons, in the final state. These have been measured inclusively [19,20,21], and in association with jets [22,23,24], W or Z bosons [25,26] (i.e. leptons and/or missing energy).…”