MEASUREMENTS OF $Z\gamma$ AND $Z\gamma\gamma$ PRODUCTION IN PP COLLISIONS AT 8 TEV WITH THE ATLAS DETECTOR

The production of Z bosons with one or two isolated high energy photons is studied using pp collisions at 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 $Z\gamma$ and $Z\gamma\gamma$ production cross sections are measured with leptonic ($e^+e^-$, $\mu^+\mu^-$, $\nu\bar{\nu}$) decays of Z bosons. 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 decay to charged leptons. Events with high photon transverse energy are used to search for anomalous triple gauge-boson couplings $ZZ\gamma$ and $Z\gamma\gamma$. Events with high diphoton invariant mass are used to search for anomalous quartic gauge-boson couplings $ZZ\gamma\gamma$ and $Z\gamma\gamma\gamma$. No statistically significant deviations from Standard Model predictions are observed and limits are placed on parameters used to describe anomalous triple and quartic gauge-boson couplings.