Measurement of the parity-violating asymmetry in inclusive electroproduction of π ^- Near the Δ0 resonance

The parity-violating (PV) asymmetry of inclusive π ^- production in electron scattering from a liquid deuterium target was measured at backward angles. The measurement was conducted as a part of the G0 experiment, at a beam energy of 360 MeV. The physics process dominating pion production for these kinematics is quasifree photoproduction off the neutron via the Δ0 resonance. In the context of heavy-baryon chiral perturbation theory, this asymmetry is related to a low-energy constant dΔ- that characterizes the parity-violating γNΔ coupling. Zhu et al. calculated dΔ- in a model benchmarked by the large asymmetries seen in hyperon weak radiative decays, and predicted potentially large asymmetries for this process, ranging from Aγ-=-5.2 to +5.2ppm. The measurement performed in this work leads to Aγ-=-0.36±1.06±0.37±0.03ppm (where sources of statistical, systematic and theoretical uncertainties are included), which would disfavor enchancements considered by Zhu et al. proportional to V _ud/V _us. The measurement is part of a program of inelastic scattering measurements that were conducted by the G0 experiment, seeking to determine the N-Δ axial transition form factors using PV electron scattering.