Eur. Phys. J. A (2007) 32: 69-75
https://doi.org/10.1140/epja/i2006-10277-3

Regular Article - Hadron Physics

Beam-helicity asymmetry in photon and pion electroproduction in the Δ(1232)-resonance region at Q² = 0.35(GeV/c)²

¹ Laboratoire de Physique Corpusculaire IN2P3-CNRS, Université Blaise Pascal, F-63170, Aubière Cedex, France
² Institut für Kernphysik, Johannes Gutenberg-Universität, D-55099, Mainz, Germany
³ C.E. Saclay, CEA Dapnia-SPhN, F-91191, Gif-sur-Yvette Cedex, France
⁴ Department of Subatomic and Radiation Physics, University of Gent, B-9000, Gent, Belgium
⁵ Department of Physics, University of Zagreb, HR-10002, Zagreb, Croatia
⁶ Institut Jožef Stefan, University of Ljubljana, SI-1001, Ljubljana, Slovenia
⁷ Dipartimento di Fisica Nucleare e Teorica, Università degli Studi di Pavia, and INFN, Sezione di Pavia, Pavia, Italy
⁸ Physik Department, Technische Universität München, D-85748, Garching, Germany
⁹ Department of Physics and Astronomy, University of Glasgow, G12 8QQ, Glasgow, UK

^* e-mail: helene@clermont.in2p3.fr

Received: 20 December 2006
Accepted: 22 February 2007
Published online: 28 March 2007

Abstract

The beam-helicity asymmetry has been measured simultaneously for the reactions p→epγ and p→epπ ⁰ in the Δ(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 γ ^(*) N→πN multipoles, mainly contributing to the non-resonant background. The beam-helicity asymmetry in both channels (γ and π ⁰) shows a good sensitivity to these multipoles and should allow future improvement in their parametrization.