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We apply current-algebra techniques to study neutrino--proton elastic scattering and neutral-current--induced soft-pion production in the case of second-class vector and axial-vector currents. (Such currents are CP-violating if the final and incident neutrinos are identical, but can be CP-conserving if the final and incident neutrinos are different particles.) The second-class currents are constructed phenomenologically from meson fields and the usual first- class V, A quark currents. The matrix elements of the second-class currents between one-nucleon states are estimated by inserting a complete set of intermediate states and saturating the sum with one-nucleon states. In this way the second-class matrix elements are expressed in terms of the experimentally measured renormalization constant of the first-class V, A currents and the pion-- nucleon coupling constants. Using standard soft-pion techniques, we analyze recently reported Brookhaven National Laboratory results for neutral-current-- induced soft-pion production under the simplifying assumption of a purely isoscalar second-class V, A neutral current. We find in this case that a second- class V--A current is consistent with the reported results. Some qualitative features of second-class neutral currents are equal cross sections for $nu$p and nu-barp elastic scattering, with only the axial-vector current contributing, and very small $nu$p and nu-barp elastic cross sectionsmore » at energies of order 50 MeV, which are relevant for possible neutrino experiments of the Los Alamos Meson Physics Facility. (AIP)« less |
