Study of the reaction νn→νpπ−

Abstract We have measured the excitation function for the neutral current process νn→νpπ− as a function of neutrino energy. Our data give a cross section ratio R=σ(νpπ−)/σ(μ−pπ+)=0.11±0.022 over the energy interval (0.3⩽E ν⩽1.5)GeV. This measurement of single-pion production in a kinematically defined reaction is the first to use a deuterium target. The R value, as well as other characteristics of the data, agrees with the Adler model for single-pion production via the neutral current and gives a value of sin2θw=0.26±0.09.