Multi-photon production in e+e- collisions at sqrt(s) = 183 GeV

TL;DR

This study measures the e+e- to gamma gamma process at 183 GeV, confirming QED predictions and setting new limits on possible new physics such as excited electrons and resonance production.

Contribution

The paper provides precise cross-section measurements at 183 GeV and establishes improved limits on QED cut-off parameters and excited electron mass, with no evidence of resonance signals.

Findings

Measured cross-section agrees with QED

Set new limits on Lambda+ and Lambda-

Established lower mass limit for excited electron

Abstract

The process e+e- to gamma gamma (gamma) is studied using data recorded with the OPAL detector at LEP. The data sample corresponds to a total integrated luminosity of 56.2 pb-1 taken at a centre-of-mass energy of 183 GeV. The measured cross-section agrees well with the expectation from QED. A fit to the angular distribution is used to obtain improved limits at 95% CL on the QED cut-off parameters: Lambda+ > 233 GeV and Lambda- > 265 GeV as well as a mass limit for an excited electron, M(e*) > 227 GeV assuming equal e*egamma and eegamma couplings. No evidence for resonance production is found in the invariant mass spectrum of photon pairs. Limits are obtained for the cross-section times branching ratio for a resonance decaying into two photons.