Cross Sections for the ReactionHe4(γ,γ)He4in theΔ(1232)-Resonance Region

We have measured the differential cross sections for coherent Compton photon scattering in the reaction ${}_{}{}^4{}_{}{}^{}\mathrm{He}(\gamma ,\gamma ){}_{}{}^4{}_{}{}^{}\mathrm{He}$ 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 $\Delta$-hole formalism for this reaction near the peak of the cross section for the $\Delta$ resonance. The results are compared to theoretical calculations in the isobar-hole model. Agreement is good for data at the energy corresponding to the $\Delta$ peak.