Study of Single Pion Production by Weak Charged Currents in Low-energy Neutrino $d$ Interactions

Abstract

This paper gives the results of a study of single-pion production by the weak charged current utilizing the wide-band muon-type-neutrino beam at the Argonne Zero Gradient Synchrotron. The data were obtained from hydrogen and deuterium fillings of the 12-ft bubble chamber. The methods of event selection and separation from background are given as are the details of the corrections and systematic effects in the data sample. The energy-dependent cross sections and differential distributions are presented for the three single-pion production reactions νp→μ−pπ+, νn→μ−pπ0, and νn→μ−nπ+. An isospin decomposition shows that the ratio of I=12 to I=32 amplitudes is 0.68±0.04 with a relative phase of (90.7±4.6)° for M(Nπ)<1.4 GeV. This agrees with theoretical models, particularly the detailed calculation of Adler. Using the data of the reaction νp→μ−pπ+, the characteristic mass of the nucleon axial-vector elastic form factor is measured to be 0.98−0.03+0.06 GeV when analyzed within the context of the Adler model. The data are also compared to other parametrizations of the nucleon axial-vector form factor.