1112.1720 (G0 Collaboration et al.)

Measurement of the parity-violating asymmetry in inclusive
electroproduction of $π^-$ near the $Δ^0$ resonance    [PDF]

G0 Collaboration, D. Androić, D. S. Armstrong, J. Arvieux, S. L. Bailey, D. H. Beck, E. J. Beise, J. Benesch, F. Benmokhtar, L. Bimbot, J. Birchall, P. Bosted, H. Breuer, C. L. Capuano, Y. -C. Chao, A. Coppens, C. A. Davis, C. Ellis, G. Flores, G. Franklin, C. Furget, D. Gaskell, M. T. W. Gericke, J. Grames, G. Guillard, J. Hansknecht, T. Horn, M. K. Jones, P. M. King, W. Korsch, S. Kox, L. Lee, J. Liu, A. Lung, J. Mammei, J. W. Martin, R. D. McKeown, A. Micherdzinska, M. Mihovilovic, H. Mkrtchyan, M. Muether, S. A. Page, V. Papavassiliou, S. F. Pate, S. K. Phillips, P. Pillot, M. L. Pitt, M. Poelker, B. Quinn, W. D. Ramsay, J. -S. Real, J. Roche, P. Roos, J. Schaub, T. Seva, N. Simicevic, G. R. Smith, D. T. Spayde, M. Stutzman, R. Suleiman, V. Tadevosyan, W. T. H. van Oers, M. Versteegen, E. Voutier, W. Vulcan, S. P. Wells, S. E. Williamson, S. A. Wood

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 quasi-free photoproduction off the neutron via the $\Delta^0$
resonance. In the context of heavy-baryon chiral perturbation theory
(HB$\chi$PT), 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 $A_\gamma^-=-0.36\pm 1.06\pm 0.37\pm 0.03$ 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.

View original: http://arxiv.org/abs/1112.1720