Study of the ZZ\gamma and Z\gamma\gamma Couplings in Z(\nu\nu)\gamma Production

TL;DR

This study measures the ZZγ and Zγγ couplings in proton-antiproton collisions, setting the most stringent limits to date on anomalous couplings using the neutrino decay channel of the Z boson.

Contribution

First measurement of hadronic Zγ production in the neutrino decay channel, providing new limits on anomalous couplings with data from the Fermilab Tevatron.

Findings

Set new 95% CL limits on anomalous couplings |h^Z_(30)| and |h^Z_(40)|.

Combined results improve constraints on anomalous couplings at different form-factor scales.

Provided the most stringent limits on these couplings to date.

Abstract

We have measured the ZZ-gamma and Z-gamma-gamma couplings by studying p-bar p -> (missing ET) gamma + X events at sqrt(s)=1.8 TeV with the D0 detector at the Fermilab Tevatron Collider. This first study of hadronic Z-gamma production in the neutrino decay channel gives the most stringent limits on anomalous couplings available. A fit to the transverse energy spectrum of the photon in the candidate event sample, based on a data set corresponding to an integrated luminosity of 13.1 pb^(-1), yields 95% CL limits on the anomalous CP-conserving ZZ-gamma couplings of |h^Z_(30)|<0.9, |h^Z_(40)|<0.21, for a form-factor scale Lambda = 500 GeV. Combining these results with our previous measurement using Z -> ee and mu-mu yields the limits:|h^Z_(30)|<0.8, |h^Z_(40)|<0.19 (Lambda = 500 GeV) and |h^Z_(30)|<0.4, |h^Z_(40)|<0.06 (Lambda = 750 GeV).