Investigation of Delta-medium effects using the He-4(gamma,pi(+)n)H-3 and He-4(gamma,pi(+)p)nnn reactions

Branford, D. et al. (2002) Investigation of Delta-medium effects using the He-4(gamma,pi(+)n)H-3 and He-4(gamma,pi(+)p)nnn reactions. Physical Review C, 66(1), 015208. (doi:10.1103/PhysRevC.66.015208)

Branford, D. et al. (2002) Investigation of Delta-medium effects using the He-4(gamma,pi(+)n)H-3 and He-4(gamma,pi(+)p)nnn reactions. Physical Review C, 66(1), 015208. (doi:10.1103/PhysRevC.66.015208)

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Abstract

Measurements of the 4He(γ,π+n)3H and 4He(γ,π+p)nnn reactions in quasifree π production kinematic regimes have been performed using unpolarized and linearly polarized tagged photons in conjunction with large solid angle π and n detectors at the MAMI-B accelerator, Mainz. Differential cross sections are presented for photon energies spanning the Δ(1232) excitation region. These data combined with previously presented results for the 12C(γ,π+n)11B reaction provide an extensive data set for future investigations of Δ-medium effects in nuclei. The 4He(γ,π+n)3H cross sections are significantly smaller than theoretical predictions based on the free proton amplitude for Δ excitation with a crude correction for final state interactions, and exhibit different trends, which could possibly be a consequence of Δ-medium effects. From a comparison with published 12C(γ,π+p)11Be data, it is concluded that the 4He(γ,π+p)nnn reaction mechanisms are probably two-step processes, although the possibility that part or all of the cross section arises from interactions with preexisting Δ++ particles cannot be ruled out.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Watts, Dr Daniel and McGeorge, Dr John and Owens, Professor Robert and MacGregor, Professor I and Annand, Dr John and Kellie, Dr James
Authors: Branford, D., Arneil, J.F., MacKenzie, J.A., Fohl, K., Ahrens, J., Annand, J.R.M., Beck, R., Franczuk, S., Grabmayr, P., Hall, S.J., Harty, P.D., Hehl, T., Kellie, J.D., Liang, M., MacGregor, I.J.D., McGeorge, J.C., Natter, A., Oberkirsch, S., Owens, R.O., Powrie, C.J.Y., Watts, D.P., and Wunderlich, S.
Subjects:Q Science > QC Physics
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Physical Review C
ISSN:0556-2813
ISSN (Online):1089-490X
Published Online:26 July 2002

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