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

Abstract

A measurement of the fiducial cross section of the associated production of a Z boson and a high-$p_\mathrm{T}$ 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}$. The fiducial Z$\gamma$ cross section, where a photon with a $p_\mathrm{T}$ greater than 225 GeV is produced in association with a Z, and the Z decays to a $\nu\bar{\nu}$ pair (Z($\nu\bar{\nu}$)$\gamma$), 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 $p_\mathrm{T}$ 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 ZZ$\gamma$ and Z$\gamma\gamma$ vertex using the $p_\mathrm{T}$ spectrum of the photons. The observed 95% confidence level intervals for $CP$-conserving $h_3^{\gamma}$ and $h_4^{\gamma}$ are determined to be ($-$3.4, 3.5) $\times$ 10$^{-4}$ and ($-$6.8, 6.8) $\times$ 10$^{-7}$, and for $h_3^\mathrm{Z}$ and $h_4^\mathrm{Z}$ they are ($-$2.2, 2.2) $\times$ 10$^{-4}$ and ($-$4.1, 4.2) $\times$ 10$^{-7}$, respectively. These are the strictest limits to date on $h_3^{\gamma}$, $h_3^\mathrm{Z}$ and $h_4^\mathrm{Z}$.