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_WWγ=290±80±16 fb, consistent with the Standard Model expectation. Including the process e⁺e⁻→νν̅γγ, limits are derived on anomalous contributions to the standard model quartic vertices W⁺W⁻γ and W⁺W⁻Zγ at 95% CL: −0.043 GeV⁻² < a_o / Λ² < −0.043 GeV⁻², −0.08 GeV-2 < a_c / Λ² < 0.13 GeV⁻², -0.41 GeV⁻² < a_n / Λ² < 0.37 GeV⁻².