A precise measurement of the cross section of the inverse muon decay νμ + e − → μ− + νe

Abstract

We report our final results from the analysis of the full high statistics sample of events of the reaction ν μ + e − → μ − + ν c collected with the CHARM II detector in the CERN wide-band neutrino beam during the years 1988 to 1991. From a signal of 15758 ± 324 inverse muon decay events we derived, inthe Born approximation, a value of (16.51 ± 0.93) × 10 −42 cm 2 GeV −1 for the asymptotic cross section slope σ E ν , in goodagreement with the Standard Model prediction of 17.23 × 10 −42 cm 2 GeV −1. The result constrains the scalar coupling of the electron and the muon to | g LL S | 2 < 0.475 at 90% CL.