Measurement of the e+e- -> Z gamma gamma Cross Section and Determination of Quartic Gauge Boson Couplings at LEP

TL;DR

This paper reports the first measurement of the e+e- -> Z gamma gamma cross section at LEP energies, confirming Standard Model predictions and setting limits on quartic gauge boson couplings.

Contribution

It provides the first experimental measurement of the Z gamma gamma production cross section and constrains quartic gauge boson couplings at LEP energies.

Findings

Measured cross sections at 182.7 GeV and 188.7 GeV are consistent with Standard Model.

Set limits on quartic gauge boson couplings a_0/Lambda^2 and a_c/Lambda^2.

Results support the Standard Model and constrain new physics.

Abstract

A first measurement of the cross section of the process e+e- -> Z gamma gamma is reported using a total integrated luminosity of 231 pb^-1 collected with the L3 detector at centre-of-mass energies of 182.7 GeV and 188.7 GeV. By selecting hadronic events with two isolated photons the e+e- -> Z gamma gamma cross section is measured to be 0.49 +0.20 -0.17 +/- 0.04 pb at 182.7 GeV and 0.47 +/- 0.10 +/- 0.04 pb at 188.7 GeV. The measurements are consistent with Standard Model expectations. Limits on Quartic Gauge Boson Couplings a_0/Lambda^2 and a_c/Lambda^2 of -0.009 GeV^-2 < a_0/Lambda^2 < 0.008 GeV^-2 and -0.007 GeV^-2 < a_c/Lambda^2 < 0.013 GeV^-2 are derived at 95% confidence level.