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

The quasielastic reaction ${\ensuremath{\nu}}_{\ensuremath{\mu}}n\ensuremath{\rightarrow}{\ensuremath{\mu}}^{\ensuremath{-}}p$ 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 ${Q}^{2}=0.06\ensuremath{-}3.00$ (${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$ were selected by kinematic fitting and particle identification and were used to extract the axial-vector form factor ${F}_{A}({Q}^{2})$ from the ${Q}^{2}$ distribution. In the framework of the conventional $V\ensuremath{-}A$ 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\ifmmode\pm\else\textpm\fi{}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.