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Measurement of the beam-helicity asymmetry in the p(e_pol,e'p)pi_0 reaction at the energy of the Delta(1232) resonance

P. Bartsch·D. Baumann·J. Bermuth·R. Boehm·K. Bohinc·D. Bosnar·M. Ding·M. Distler·D. Drechsel·D. Elsner·I. Ewald·J. Friedrich·J. M. Friedrich·S. Groezinger·S. Hedicke·P. Jennewein·M. Kahrau·S. S. Kamalov·F. Klein·K. W. Krygier·A. Liesenfeld·H. Merkel·P. Merle·U. Mueller·R. Neuhausen·Th. Pospischil·M. Potokar·G. Rosner·H. Schmieden·M. Seimetz·A. Suele·L. Tiator·A. Wagner·Th. Walcher·M. Weis
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Abstract

In a p(e_pol,e'p)pi_0 out-of-plane coincidence experiment at the 3-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 lack of understanding of the non-resonant background, which in dynamical models is related to the pion cloud.

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P. Bartsch, D. Baumann, J. Bermuth, R. Boehm, K. Bohinc, D. Bosnar, M. Ding, M. Distler, D. Drechsel, D. Elsner, I. Ewald, J. Friedrich, J. M. Friedrich, S. Groezinger, S. Hedicke, P. Jennewein, M. Kahrau, S. S. Kamalov, F. Klein, K. W. Krygier, A. Liesenfeld, H. Merkel, P. Merle, U. Mueller, R. Neuhausen, Th. Pospischil, M. Potokar, G. Rosner, H. Schmieden, M. Seimetz, A. Suele, L. Tiator, A. Wagner, Th. Walcher, M. Weis. 2001-12-18. Measurement of the beam-helicity asymmetry in the p(e_pol,e'p)pi_0 reaction at the energy of the Delta(1232) resonance. https://doi.org/10.1103/physrevlett.88.142001

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