Search for the Lepton Number Violating Process µe → µ e

The NuTeV experiment at Fermilab has used a sign-selected neutrino beam to perform a search for the lepton number violating process �µe → µ �e, and to measure the cross-section of the Standard Model inverse muon decay process �µe → µ �e. NuTeV measures the inverse muon decay asymptotic cross-section �/E to be (13.8 ±1.2 ±1.4) ×10 42 cm 2 /GeV. The experiment also observes no evidence for lepton number violation and places one of the most restrictive limits on the cross-section ratio �(�µe → µ �e)/�(�µe → µ �e) ≤ 1.7% at 90% C.L. for V−A couplings and ≤ 0.6% for scalar couplings.