A total of ∼ 249 000 neutrino interactions were observed at Fermilab in a high-angular-resolution electromagnetic shower detector, with ∼ 0.947× ${10}^{19}$ protons of 350-GeV energy incident upon the production target. Based on a data sample of 0.71×${10}^{19}$ protons, 46 electrons were observed with ${\theta }_e<~10$ mrad. Of these 46 events, 34 are attributed to the process ${\nu }_{\mu }+e^{-}\to {\nu }_{\mu }+e^{-}$, and 12 are attributed to background processes. This leads to the following results: $\sigma =(1.40\mathrm{}\pm 0.30)\times {10}^{-42\mathrm{}}{E}_{\nu }$ ${\mathrm{cm}}^2$ and ${{sin}^2\theta }_{\mathrm{W}}={0.25}_{-0.05\mathrm{}}^{+0.07\mathrm{}}$.

• Received 20 September 1979

DOI:https://doi.org/10.1103/PhysRevLett.44.635