WWγ vertex in radiative muon decay

Large numbers of muons will be produced at facilities developed to probe lepton flavor violating process μ → eγ. We show that by constructing a suitable asymmetry, radiative muon decay μ → eγνμν̄e can also be used to test the WWγ vertex at such facilities. The process has two missing neutrinos in the final state and on integrating their momenta, the partial differential decay rate shows no radiation-amplitude-zero. We establish, however, that an easily separable part of the normalized differential decay rate, odd under the exchange of photon and electron energies, does have a zero in the case of standard model (SM). This new type of zero has hitherto not been studied in literature. A suitably constructed asymmetry using this fact, enables a sensitive probe for the WWγ vertex beyond the SM. With a simplistic analysis, we find that the C and P conserving dimension four WWγ vertex can be probed at O(10−2) with satisfactory significance level.