A study of W⁺ W⁻ γ events at LEP

A study of W+W- events accompanied by hard photon radiation, Egamma > 2.5 GeV, produced in e(+)e(-) collisions at LEP is presented. Events consistent with being two on-shell W-bosons and an isolated photon are selected from 681 pb(-1) of data recorded at 180 GeV <roots <209 GeV. From the sample of 187 selected W(+)W(-)gamma candidates with photon energies greater than 2.5 GeV, the W(+)W(-)gamma cross-section is determined at five values of roots. The results are consistent with the Standard Model expectation. Averaging over all energies, the ratio of the observed cross-section to the Standard Model expectation is R(data/SM) = 0.99 +/- 0.09 +/- 0.04, where the errors represent the statistical and systematic uncertainties respectively. These data provide constraints on the related O(alpha) systematic uncertainties on the measurement of the W-boson mass at LEP. Finally, the data are used to derive 95% confidence level upper limits on possible anomalous contributions to the W(+)W(-)gammagamma and W(+)W(-)Z(0)y vertices: -0.020 GeV-2 <a(0)/Lambda(2) <0.020 GeV-2, -0.053 GeV-2 <a(c)/Lambda(2) <0.037 GeV-2, -0.16 GeV-2 <a(n)/Lambda(2) <0.15 GeV-2, where Lambda represents the energy scale for new physics and a(0), a(c) and a(n) are dimensionless coupling constants. (C) 2003 Elsevier B.V. All rights reserved.