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Measurement of the parity-violating asymmetry in inclusive electroproduction of $\pi^-$ near the $\Delta^0$ resonance

Abstract : 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.
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Submitted on : Friday, December 9, 2011 - 11:22:16 AM
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D. Androić, D.S. Armstrong, J. Arvieux, S. L. Bailey, D. H. Beck, et al.. Measurement of the parity-violating asymmetry in inclusive electroproduction of $\pi^-$ near the $\Delta^0$ resonance. Physical Review Letters, American Physical Society, 2012, 108, pp.122002. ⟨10.1103/PhysRevLett.108.122002⟩. ⟨in2p3-00649981⟩



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