Beam-helicity asymmetry in photon and pion electroproduction in the Delta(1232) resonance region at Q^2= 0.35 (GeV/c)^2

Abstract

The beam-helicity asymmetry has been measured simultaneously for the reactions (e p \to e p \gamma) and (e p \to e p \pi^0) in the $\Delta (1232)$ resonance region at $Q^2=$ 0.35 (GeV/c)$^2$. The experiment was performed at MAMI with a longitudinally polarized beam and an out-of-plane detection of the proton. The results are compared with calculations based on Dispersion Relations for virtual Compton scattering and with the MAID model for pion electroproduction. There is an overall good agreement between experiment and theoretical calculations. The remaining discrepancies may be ascribed to an imperfect parametrization of some $\gamma^{(*)} N \to \pi N$ multipoles, mainly contributing to the non-resonant background. The beam-helicity asymmetry in both channels ($\gamma$ and $\pi^0$) shows a good sensitivity to these multipoles and should allow future improvement in their parametrization.Comment: 7 pages, 8 figures, version to appear in EPJ