Quasielastic neutrino scattering: A measurement of the weak nucleon axial-vector form factor

The quasielastic reaction ${\nu }_{\mu }n\to {\mu }^{-}p$ was studied in an experiment using the BNL 7-foot deuterium bubble chamber exposed to the wide-band neutrino beam with an average energy of 1.6 GeV. A total of 1138 quasielastic events in the momentum-transfer range $Q^2=0.06-3.00\mathrm{}$ (${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ were selected by kinematic fitting and particle identification and were used to extract the axial-vector form factor $F_A\left(Q^2\right)$ from the $Q^2$ distribution. In the framework of the conventional $V-A$ theory, we find that the dipole parametrization is favored over the monopole. The value of the axial-vector mass $M_A$ in the dipole parametrization is 1.07±0.06 GeV, which is in good agreement with both recent neutrino and electroproduction experiments. In addition, the standard assumptions of conserved vector current and no second-class currents are checked.