Electroweak pion production on nuclei within the extended factorization scheme

We have applied the extended factorization scheme to investigate the electroweak pion production on nuclei. The ANL-Osaka model, which was obtained by analyzing the data of pi N, gamma N, N(e, e'pi), and N(nu, mu pi) reactions up to invariant mass W = 2 GeV, is used to generate the matrix elements of current operators relevant to pion production off the nucleon. Medium effects on the Delta (1232) component of the meson-exchange current are included by using a Delta-nucleus potential determined from the previous Delta-hole model studies of pion-nucleus reactions. Nuclear correlations in the initial target state and in the spectator system(s) are modeled using realistic hole spectral functions. As a first step, we show that the data of C-12(e, e') up to the Delta (1232) region can be described reasonably well. The interplay between the pion production and two-body meson-exchange mechanisms is shown to be essential in improving the agreement with the data in the "dip" region, between the quasielastic and the Delta (1232) peaks. Predictions for 12C(nu, mu pi) have also been made. They can be used to estimate pion-emission rates in neutrino-nucleus cross section, which constitutes an important systematic uncertainty to the reconstructed neutrino energy. With further improvements of the Metropolis Monte Carlo techniques to account for final states comprised of more than two particles, our approach can be employed up to W = 2 GeV, where two-pion production and higher mass nucleon resonances must be included for analyzing the data from accelerator-based neutrino-oscillation experiments.