First Observation and Cross-Section Measurement ofνe+e−→νe+e−

We report the first observation and cross-section measurement of ${\nu }_e+e^{-}\to {\nu }_e+e^{-}$. Using neutrinos of energy less than 53 MeV, we observed 63±17 events consistent with $\nu +e^{-}\to \nu +e^{-}$, of which 51±17 events are assigned to ${\nu }_e+e^{-}\to {\nu }_e+e^{-}$. The resulting cross section, {[8.9±3.2(statistical) ±1.5(systematic)]×${10}^{-45\mathrm{}}$ ${\mathrm{cm}}^2$/MeV} $E_{\nu }$, agrees with standard electroweak theory, rules out constructive interference between weak charged-current and neutral-current interactions, and begins to indicate the existence of interference between these two interactions.