Measurement of the Zγ 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- p T 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 $\sqrt{s}=13$ TeV during 2016–2018, corresponding to an integrated luminosity of 138 fb − 1 . The fiducial Zγ cross section, where a photon with a p T greater than 225 GeV is produced in association with a Z, and the Z decays to a $\upnu \overline{\upnu}$ pair $\left(\mathrm{Z}\left(\upnu \overline{\upnu}\right)\upgamma \right)$ , is measured to be ${23.3}_{-1.3}^{+1.4}$ fb, in agreement, within uncertainties, with the standard model prediction. The differential cross section as a function of the photon p T 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 Zγγ vertex using the p T spectrum of the photons. The observed 95% confidence level intervals for CP -conserving ${h}_3^{\upgamma}$ and ${h}_4^{\upgamma}$ are determined to be ( − 3.4, 3.5) × 10 − 4 and ( − 6.8, 6.8) × 10 − 7 , and for ${h}_3^{\mathrm{Z}}$ and ${h}_4^{\mathrm{Z}}$ they are ( − 2.2, 2.2) × 10 − 4 and ( − 4.1, 4.2) × 10 − 7 , respectively. These are the strictest limits to date on ${h}_3^{\upgamma}$ , ${h}_3^{\mathrm{Z}}$ and ${h}_4^{\mathrm{Z}}$ .