Multi-photon final states in e^+e^- collisions at sqrt{s} = 130-172 GeV

TL;DR

This study measures multi-photon production in electron-positron collisions at energies of 130-172 GeV, confirming QED predictions and setting new limits on possible new physics phenomena such as contact interactions and excited electrons.

Contribution

The paper provides the first combined analysis of multi-photon final states at these energies, improving limits on non-standard couplings and excited electron masses.

Findings

Measured cross-sections agree with QED

Set limits on cut-off parameters: Lambda_+ > 195 GeV, Lambda_- > 210 GeV

Established a 95% CL mass limit for excited electrons: M_{e^*} > 194 GeV

Abstract

The process e^+e^- -> gamma gamma (gamma) is studied using data recorded with the OPAL detector at LEP. The data sample corresponds to a total integrated luminosity of 25.38 pb^{-1} taken at centre-of-mass energies of 130-172 GeV. The measured cross-sections agree well with the expectation from QED. In a combined fit using data from all centre-of-mass energies, the angular distribution is used to obtain improved limits on the cut-off parameters: Lambda_+ > 195 GeV and Lambda_- > 210 GeV (95% CL). In addition, limits on non-standard e^+e^-gamma couplings and contact interactions, as well as a 95% CL mass limit for an excited electron, M_{e^*} > 194 GeV for an e^+e^-gamma coupling kappa = 1, are determined.