ATLAS_2016_I1448301 in pool ATLAS_8_MM_GAMMA

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The production of $Z$ bosons with one or two isolated high-energy photons is studied using pp collisions at $\sqrt{s}=8$ 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 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 $E_\text{T}>250$ GeV from $\ell^+\ell^-\gamma$ events and with $E_\text{T}>400$ GeV from $\nu\bar{\nu}\gamma$ events are used to search for anomalous triple gauge-boson couplings $ZZ\gamma$ and $Z\gamma\gamma$. The yields of events with diphoton invariant mass $m_{\gamma\gamma}>200$ GeV from $\ell^+\ell^-\gamma\gamma$ events and with $m_{\gamma\gamma}>300$ GeV from $\nu\bar{\nu}\gamma\gamma$ events are used to search for anomalous quartic gauge-boson couplings $ZZ\gamma\gamma$ and $Z\gamma\gamma\gamma$. No deviations from Standard Model predictions are observed and limits are placed on parameters used to describe anomalous triple and quartic gauge-boson couplings. The lepton channel can be specified by using the relevant LMODE (EL, MU, NU, LL). The default plugin will fill all of them with any events passing the cuts. NU will do only the MET channels, EL & MU will do only the electron or muon and will populate the combined plots assuming charged lepton universality. LL with do on the electron and muon but will populate the combined plots with the average of the two.


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