We have measured the differential cross sections for coherent Compton photon scattering in the reaction 4 He(/,y) 4 He at laboratory angles of 24°, 30°, 45°, and 60° with an average laboratory photon energy of 320 MeV, at 22° with 358 MeV, and at 30° with 260 MeV. These measurements are the first unambiguous test of the A-hole formalism for this reaction near the peak of the cross section for the A resonance. The results are compared to theoretical calculations in the isobar-hole model. Agreement is good for data at the energy corresponding to the A peak.PACS numbers: 25.20.Dc, 25.10,+s An important topic in intermediate-energy physics is the creation and propagation of the A(1232) resonance inside the nucleus. Compton scattering creates the A deep inside the nucleus, in contrast to pion scattering and photopion production which are dominated by interactions at the nuclear surface. Additionally, there are no initial-or final-state interactions to complicate the interpretation of the Compton-scattering data.tion. Koch, Moniz, and Ohtsuka 2 use a "spreading potential," whose parameters are adjusted to give a good fit to pion elastic-scattering data, to account for the more complicated decay channels. The model then gives predictions for /r° photoproduction and elastic photon scattering with no further adjustable parameters. Good elastic photon-scattering data over the whole angular range will help our understanding of the A resonance in li blocking of A decay or coupling to more complicated channels through absorption in the NN channels. The propagator can then be used to describe a variety of reactions. This has been applied with considerable success to pion-nucleus scattering and coherent /r° photoproduc-and Pb targets, but the data may have included a large contribution from incoherent channels due to insufficient photon energy resolution. The amount of incoherent scattering is consistent with the estimates calculated by Arenhovel. 6 We have previously published results for TOP VIEW 1922 FIG. 1. Schematic diagram of the experimental setup.

No abstract