Abstract: ABSTRACT: The first observation of the electroweak (EW) production of a Z boson, a photon, and two forward jets (Z?jj) in proton-proton collisions at a center-of-mass energy of 13 TeV is presented. A data set corresponding to an integrated luminosity of 137??fb?1, collected by the CMS experiment at the LHC in 2016?2018 is used. The measured fiducial cross section for EW Z?jj is ?EW=5.21±0.52(stat)±0.56(syst)??fb=5.21±0.76??fb. Single-differential cross sections in photon, leading lepton, and leading jet transverse momenta, and double-differential cross sections in mjj and |??jj| are also measured. Exclusion limits on anomalous quartic gauge couplings are derived at 95% confidence level in terms of the effective field theory operators M0 to M5, M7, T0 to T2, and T5 to T9.
