Measurement of the beam-helicity asymmetry in the p((-->)e,e'p)pi(0) reaction at the energy of the Delta(1232) resonance.

@article{Bartsch2002MeasurementOT,
title={Measurement of the beam-helicity asymmetry in the p((-->)e,e'p)pi(0) reaction at the energy of the Delta(1232) resonance.},
author={P. Bartsch and D. Baumann and J. Bermuth and R. B{\"o}hm and K. Bohinc and D. Bosnar and M. Ding and M. Distler and D. Drechsel and D. Elsner and I. Ewald and J. Friedrich and S. Gr{\"o}zinger and S. Hedicke and P. Jennewein and M. Kahrau and S. Kamalov and F. Klein and K. W. Krygier and A. Liesenfeld and H. Merkel and P. Merle and U. Mueller and R. Neuhausen and T. Pospischil and M. Potokar and G. Rosner and H. Schmieden and M. Seimetz and A. Suele and L. Tiator and A. Wagner and T. Walcher and M. Weis},
journal={Physical review letters},
year={2002},
volume={88 14},
pages={
142001
}
}

In a p((-->)e,e'p)pi(0) out-of-plane coincidence experiment at the three-spectrometer setup of the Mainz Microtron MAMI, the beam-helicity asymmetry has been precisely measured around the energy of the Delta(1232) resonance and Q(2) = 0.2(GeV/c)(2). The results are in disagreement with three up-to-date model calculations. This is interpreted as a lack of understanding of the nonresonant background, which in dynamical models is related to the pion cloud.