Measurements of the γ∗p→Δ reaction at low Q2: Probing the mesonic contribution

Stave, S. and Sparveris, N. and Distler, M. O. and Nakagawa, I. and Achenbach, P. and Gayoso, C. Ayerbe and Baumann, D. and Bernauer, J. and Bernstein, A. M. and Bohm, R. and Bosnar, Damir and Botto, T. and Christopoulou, A. and Dale, D. and Ding, M. and Doria, L. and Friedrich, J. and Karabarbounis, A. and Makek, Mihael and Merkel, H. and Muller, U. and Neuhausen, R. and Nungesser, L. and Papanicolas, C. N. and Piegsa, A. and Pochodzalla, J. and Potokar, M. and Seimetz, M. and Širca, S. and Stiliaris, S. and Walcher, Th. and Weis, M. (A1 Collaboration) (2008) Measurements of the γ∗p→Δ reaction at low Q2: Probing the mesonic contribution. Physical Review C, 78 (2). pp. 25209-18. ISSN 0556-2813

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The determination of nonspherical angular momentum amplitudes in nucleons at long ranges (low Q2) was accomplished through the p(, e'p)0 reaction in the region at Q2=0.060, 0.127, and 0.200 (GeV/c)2 at the Mainz Microtron with an accuracy for the cross sections of 4%. The results for the dominant transition magnetic dipole amplitude and the quadrupole to dipole ratios have been obtained with an estimated model uncertainty that is approximately the same as the experimental uncertainty. Lattice and effective field theory predictions agree with our data within the relatively large estimated theoretical uncertainties. Phenomenological models are in good agreement with experiment when the resonant amplitudes are adjusted to the data. To check reaction model calculations additional data were taken for center-of-mass energies below resonance and for the LT' structure function. These results confirm the dominance, and general Q2 variation, of the pionic contribution at large distances.

Item Type: Article
Keywords: meson production, baryon resonances with S=0
Date: August 2008
Subjects: NATURAL SCIENCES > Physics
Additional Information: Copyright (2008) by the American Physical Society.
Divisions: Faculty of Science > Department of Physics
Project code: 119-1191005-1021
Publisher: American Physical Society
Depositing User: Gordana Stubičan Ladešić
Date Deposited: 03 Jun 2014 11:35
Last Modified: 27 Feb 2016 07:26

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