Measurement of the Z gamma production cross section and search for anomalous neutral triple gauge couplings in pp collisions at sqrt(s) = 13 TeV

A measurement of the fiducial cross section of the associated production of a Z boson and a high-pT photon, where the Z decays to two neutrinos, and a search for anomalous triple gauge couplings are reported. The results are based on data collected by the CMS experiment at the LHC in proton-proton collisions at √s = 13 TeV during 2016–2018, corresponding to an integrated luminosity of 138 fb−1. The fiducial Zγ cross section, where a photon with a pT greater than 225 GeV is produced in association with a Z, and the Z decays to a νν pair (Z(νν)γ ), is measured to be 23.3 +1.4 −1.3 fb, in agreement, within uncertainties, with the standard model prediction. The differential cross section as a function of the photon pT has been measured and compared with standard model predictions computed at next-to-leading and at next-to-next-to-leading order in perturbative quantum chromodynamics. Constraints have been placed on the presence of anomalous couplings that affect the ZZγ and Zγ γ vertex using the pT spectrum of the photons. The observed 95% confidence level intervals for CP-conserving h γ 3 and h γ 4 are determined to be (−3.4, 3.5)×10−4 and (−6.8, 6.8)×10−7, and for h Z 3 and h Z 4 they are (−2.2, 2.2)×10−4 and (−4.1, 4.2)×10−7, respectively. These are the strictest limits to date on h γ 3, h Z 3 and h Z 4.