Measurements ofZγandZγγproduction inppcollisions ats=8 TeVwith the ATLAS detector

The production of $Z$ bosons with one or two isolated high-energy photons is studied using $pp$ collisions at $\sqrt{s}=8\text{ }\text{ }\mathrm{TeV}$. The analyses use a data sample with an integrated luminosity of $20.3\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ collected by the ATLAS detector during the 2012 LHC data taking. The $Z\ensuremath{\gamma}$ and $Z\ensuremath{\gamma}\ensuremath{\gamma}$ production cross sections are measured with leptonic (${e}^{+}{e}^{\ensuremath{-}}$, ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$, $\ensuremath{\nu}\overline{\ensuremath{\nu}}$) 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 ${E}_{\mathrm{T}}g250\text{ }\text{ }\mathrm{GeV}$ from ${\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}\ensuremath{\gamma}$ events and with ${E}_{\mathrm{T}}g400\text{ }\text{ }\mathrm{GeV}$ from $\ensuremath{\nu}\overline{\ensuremath{\nu}}\ensuremath{\gamma}$ events are used to search for anomalous triple gauge-boson couplings $ZZ\ensuremath{\gamma}$ and $Z\ensuremath{\gamma}\ensuremath{\gamma}$. The yields of events with diphoton invariant mass ${m}_{\ensuremath{\gamma}\ensuremath{\gamma}}g200\text{ }\text{ }\mathrm{GeV}$ from ${\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}\ensuremath{\gamma}\ensuremath{\gamma}$ events and with ${m}_{\ensuremath{\gamma}\ensuremath{\gamma}}g300\text{ }\text{ }\mathrm{GeV}$ from $\ensuremath{\nu}\overline{\ensuremath{\nu}}\ensuremath{\gamma}\ensuremath{\gamma}$ events are used to search for anomalous quartic gauge-boson couplings $ZZ\ensuremath{\gamma}\ensuremath{\gamma}$ and $Z\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\gamma}$. No deviations from Standard Model predictions are observed and limits are placed on parameters used to describe anomalous triple and quartic gauge-boson couplings.