Production of single W bosons at √s = 189 GeV and measurement of WWγ gauge couplings

Abstract Single W boson production in electron-positron collisions is studied with the L3 detector at LEP. The data sample collected at a centre-of-mass energy of s =188.7 GeV corresponds to an integrated luminosity of 176.4 pb −1 . Events with a single energetic lepton or two acoplanar hadronic jets are selected. Within phase-space cuts, the total cross-section is measured to be 0.53±0.12±0.03 pb , consistent with the Standard Model expectation. Including our single W boson results obtained at lower s , the WW γ gauge couplings κ γ and λ γ are determined to be κ γ =0.93±0.16±0.09 and λ γ =−0.31 +0.68 −0.19 ±0.13.