Constraints on Anomalous Quaric Gauge Boson Couplings from vv gamma gamma and qq gamma gamma events at LEP 2

TL;DR

This paper analyzes LEP2 OPAL data to measure processes involving photon pairs and constrains possible anomalous quartic gauge couplings, setting limits on new physics parameters at 95% confidence level.

Contribution

It provides the first combined constraints on anomalous quartic gauge couplings using vv gamma gamma and qq gamma gamma events at LEP2 energies.

Findings

Measured the cross-section ratio R(data/SM) = 0.92 +- 0.07 +- 0.04.

Set 95% CL limits on anomalous coupling parameters aoz, acz, aow, acw.

Combined results with previous OPAL analyses for improved constraints.

Abstract

Anomalous quartic couplings between the electroweak gauge bosons may contribute to the vv gamma gamma and qq gamma gamma final states produced in e+e- collisions. This analysis uses the LEP2 OPAL data sample at centre-of-mass energies up to 209 GeV. Event selections identify vv gamma gamma and qq gamma gamma events in which the two photons are reconstructed within the detector acceptance. The cross-section for the process e+e- -> qq gamma gamma is measured. Averaging over all energies, the ratio of the observed e+e- -> qq gamma gamma cross-section to the Standard Model expectation is R(data/SM) = 0.92 +- 0.07 +- 0.04 where the errors represent the statistical and systematic uncertainties respectively. The vv gamma gamma and qq gamma gamma data are used to constrain possible anomalous W+W- gamma gamma and ZZ gamma gamma couplings. Combining with previous OPAL results from the W+W- gamma final state, the 95% confidence level limits on the anomalous coupling parameters aoz, acz, aow and acw are found to be: -0.007 GeV^-2 < aoz/Lambda^2 < 0.023 GeV^-2 -0.029 GeV^-2 < acz/Lambda^2 < 0.029 GeV^-2 -0.020 GeV^-2 < aow/Lambda^2 < 0.020 GeV^-2 -0.052 GeV^-2 < acw/Lambda^2 < 0.037 GeV^-2 where Lamdba is the energy scale of the new physics. Limits found when allowing two or more parameters to vary are also presented.