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

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 $36.1{\mathrm{f}\mathrm{b}}^{-1}$. 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{E}\mathrm{W}$} = 7.8 ; \pm 2.0 ; $\mathrm{f}\mathrm{b}$$, in good agreement with the Standard Model prediction.