A Precise measurement of the cross-section of the inverse muon decay muon-neutrino + e- --> mu- + electron-neutrino

We report our final results from the analysis of the full high statistics sample of events of the reaction up + e- --+ /*- + v, collected with the CHARM II detector in the CERN wide-band neutrino beam during the years 1988 to 1991. From a signal of 15 758 f 324 inverse muon decay events we derived, in the Born approximation, a value of ( 16.51 f 0.93) x lO-42 cm*GeV-’ for the asymptotic cross section slope a/E,, in good agreement with the Standard Model prediction of 17.23 x IO-” cm* GeV- ‘. The result constrains the scalar coupling of the electron and the muon to [&l’ < 0.475 at 90% CL.