Measurement of the W +W −γ cross section and direct limits on anomalous quartic gauge boson couplings at LEP

Abstract

The process e +e −→W +W − γ is analysed using the data collected with the L3 detector at LEP at a centre-of-mass energy of 188.6 GeV , corresponding to an integrated luminosity of 176.8 pb −1. Based on a sample of 42 selected W +W − candidates containing an isolated hard photon, the W +W − γ cross section, defined within phase-space cuts, is measured to be: σ WW γ =290±80±16 fb, consistent with the Standard Model expectation. Including the process e +e − →ν ν ̄ γγ , limits are derived on anomalous contributions to the Standard Model quartic vertices W +W − γγ and W +W −Z γ at 95% CL: −0.043 GeV −2<a 0/Λ 2<0.043 GeV −2 , −0.08 GeV −2<a c/Λ 2<0.13 GeV −2 , −0.41 GeV −2<a n/Λ 2<0.37 GeV −2 .