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

The quasielastic reaction ν_μn→μ^-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 Q²=0.06-3.00 (GeV/c)² were selected by kinematic fitting and particle identification and were used to extract the axial-vector form factor FA(Q²) from the Q² 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 MA 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.