Wrong-Helicity Electrons in Radiative Muon Decay

We have studied in detail the spectrum of the decay μ− → e−ν̄eνμγ as a function of the electron helicity, and verify the prediction [1] that a significant fraction of the electrons in this decay is righthanded. These “wrong-helicity” electrons persist in the limit λ = me/mμ → 0, and are connected with helicity-flip bremsstrahlung in QED. The longitudinal polarization of the electron is calculated as a function of the photon and electron energy, and deviates systematically from the naive V-A prediction PL = −1. The right-handed component is concentrated in the collinear region θ . me/Ee. In the limit λ → 0, we reproduce the results obtained in [1] using the helicity-flip splitting function introduced by Falk and Sehgal.