Testing WWγ vertex in radiative muon decay

Abstract

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 → eγνµνe can also be used to test the W W γ 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 W W γ vertex beyond the SM. With a simplistic analysis, we find that the C and P conserving dimension four W W γ vertex can be probed at O(10 −2 ) with satisfactory significance level.