Study of the isospin structure of single-pion production in charged-current neutrino interactions

Abstract

The isospin structure of weak single-pion production in the reactions $\ensuremath{\nu}p\ensuremath{\rightarrow}{\ensuremath{\mu}}^{\ensuremath{-}}p{\ensuremath{\pi}}^{+}$, $\ensuremath{\nu}n\ensuremath{\rightarrow}{\ensuremath{\mu}}^{\ensuremath{-}}p{\ensuremath{\pi}}^{0}$, and $\ensuremath{\nu}n\ensuremath{\rightarrow}{\ensuremath{\mu}}^{\ensuremath{-}}n{\ensuremath{\pi}}^{+}$ has been studied using the 7-foot deuterium bubble chamber exposed to a wide-band neutrino beam at BNL. We find that the $I=\frac{1}{2}N\ensuremath{\pi}$ amplitude is substantial even in the $\ensuremath{\Delta}(1232)$ mass region and the relative phase angle $\ensuremath{\psi}$ is approximately 90\ifmmode^\circ\else\textdegree\fi{} as predicted by the Adler model.