Lepton mass effects in single pion production by neutrinos

We reconsider the Feynman-Kislinger-Ravndal model applied to neutrino-excitation of baryon resonances. The effects of lepton mass are included, using the formalism of Kuzmin, Lyubushkin, and Naumov. In addition we take account of the pion-pole contribution to the hadronic axial vector current. Application of this new formalism to the reaction nu(mu)+p ->mu(-)+Delta(++) at E-nu similar to 1 GeV gives a suppressed cross section at small angles, in agreement with the screening correction in Adler's forward-scattering theorem. Application to the process nu(tau)+p ->tau(-)+Delta(++) at E-nu similar to 7 GeV leads to the prediction of right-handed tau(-) polarization for forward-going leptons, in line with a calculation based on an isobar model. Our formalism represents an improved version of the Rein-Sehgal model, incorporating lepton mass effects in a manner consistent with partially conserved axial-vector current.