Physical Review Letters
The parity-violating (PV) asymmetry of inclusive pi(-) 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 Delta(0) resonance. In the context of heavy-baryon chiral perturbation theory, this asymmetry is related to a low-energy constant d(Delta)(-) that characterizes the parity-violating gamma N Delta coupling. Zhu et al. calculated d(Delta)(-) in a model benchmarked by the large asymmetries seen in hyperon weak radiative decays, and predicted potentially large asymmetries for this process, ranging from A(gamma)(-) = -5.2 to + 5.2 ppm. The measurement performed in this work leads to A(gamma)(-) = -0.36 +/- 1.06 +/- 0.37 +/- 0.03 ppm (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 - Delta axial transition form factors using PV electron scattering.
Androić, D., Armstrong, D. S., Arvieux, J., Bailey, S. L., Beck, D. H., Beise, E. J., ... & Bosted, P. (2012). Measurement of the Parity-Violating Asymmetry in Inclusive Electroproduction of π− near the Δ 0 Resonance. Physical review letters, 108(12), 122002.