A precise measurement of the cross section of the inverse muon decay $\nu_{\mu}$ + e$^{-}$ --> $\mu^{-}$ + $\nu_{e}$

We report our final results from the analysis of the full high statistics sample of events of the reaction \imd\,\, collected with the \CHARMII{} detector in the CERN wide-band neutrino beam during the years 1988 to~1991. From a signal of 15,758 \pm 324 inverse muon decay events we derived, in the Born approximation, a value of (16.51 \pm 0.93) \times 10^{-42} \unit{cm}^2 \unit{GeV}^{-1} for the asymptotic cross section slope \sigma/E_\nu, in good agreement with the Standard Model prediction of 17.23 \times 10^{-42} \unit{cm}^2 \unit{GeV}^{-1}. The result constrains the scalar coupling of the electron and the muon to |\gLL{S}|^2 < 0.475\ \rm{at}\ 90\%\ \rm{CL}.