Two-Body Photodisintegration of 3He, 4He, and 2He up to 1.5 GeV

B.L. Berman, George Washington University

We have obtained data on all of the photoreaction channels of 3He and 4He, from 0.35 to 1.5 GeV, using liquid targets, the Photon Tagger, and the CEBAF Large-Acceptance Spectrometer in Hall B at Jefferson Lab. Our data for the three-body photodisintegration of 3He already have shown strong evidence for the importance of three-body mechanisms. Here we report preliminary results for three other reaction channels. Cross sections for the 3He(g,dp) and 4He(g,tp) reactions are compared with the model predictions of Laget to throw further light on three-body mechanisms and thus to reaffirm their importance. The angular distribution for the 4He(g,dd) channel shows no evidence for dipole reactions, and the consequent breaking of isospin symmetry, in contrast with earlier results at lower energies. And selecting only those 3He(g,pp)n events where the neutron is a spectator enables us to study the two-body photodisintegration of 2He, with surprising results, in preparation for an upcoming experiment in Hall A at Jefferson Lab on hard-pp quark-exchange processes.

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