Evidence for electroweak production of two jets in association with a $Z\gamma$ pair in $pp$ collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector

Abstract

Evidence for electroweak production of two jets in association with a $Z\gamma$ pair in $\sqrt{s} = 13$ TeV proton$-$proton collisions at the Large Hadron Collider is presented. The analysis uses data collected by the ATLAS detector in $2015$ and $2016$ that corresponds to an integrated luminosity of $36.1~\mathrm{fb}^{-1}$. Events that contain a $Z$ boson candidate decaying leptonically into either $e^{+}e^{-}$ or $\mu^{+}\mu^{-}$, a photon, and two jets are selected. The electroweak component is measured with observed and expected significances of $4.1$ standard deviations. The fiducial cross-section for electroweak production is measured to be $\sigma_{Z\gamma jj\mathrm{-EW}} = 7.8 \; \pm 2.0 \; \mathrm{fb}$, in good agreement with the Standard Model prediction.