Lepton mass effects in single pion production by neutrinos

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Abstract
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) approx 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) approx 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 PCAC.Comment: 14 pages, 5 figures. Typos in eq. 9 and 27 corrected. Numbers in table I for coherent cross sections (RSA and RSC) corrected (normalization error). Figs 3 and 4 changed accordingly. These corrections also apply to the published version PRD 76, 113004 (2007