The e+e- -> Z gamma gamma -> q q gamma gamma Reaction at LEP and Constraints on Anomalous Quartic Gauge Boson Couplings

TL;DR

This study measures the e+e- -> Z gamma gamma process at LEP energies, finds results consistent with the Standard Model, and sets new limits on anomalous quartic gauge boson couplings.

Contribution

It provides the first experimental constraints on anomalous quartic gauge boson couplings using LEP data at 205-207 GeV.

Findings

No deviation from Standard Model observed.

Constraints on anomalous couplings: -0.02 to 0.03 GeV^-2 for a_0/Λ^2.

Constraints on a_c/Λ^2: -0.07 to 0.05 GeV^-2.

Abstract

The cross section of the process e^+ e^- -> Z \gamma\gamma -> qq \gamma \gamma is measured with 215 pb^-1 of data collected with the L3 detector during the final LEP run at centre-of-mass energies around 205 GeV and 207 GeV. No deviation from the Standard Model expectation is observed. The full data sample of 713 pb^-1, collected above the Z resonance, is used to constrain the coefficients of anomalous quartic gauge boson couplings to: -0.02 GeV^-2 < a_0/\Lambda^2 < 0.03 GeV^-2 and -0.07 GeV^-2 < a_c/\Lambda^2 < 0.05 GeV^-2, at 95% confidence level.