Two-Body Photodisintegration of $^{3}$He, $^{4}$He, and $^{2}$He up to 1.5 GeV

We have obtained data on all of the photoreaction channels of $^{3}$He and $^{4}$He, from 0.35 to 1.5 GeV, using liquid targets, the Photon Tagger, and the CLAS in Hall B at Jefferson Lab. Our data for the three-body photodisintegration of $^{3}$He and its evidence for three-body mechanisms have been published.$^{1}$ Here we report preliminary results for three other reaction channels as well as a more detailed analysis of the data of Ref. 1. Cross sections for the $^{3}$He($\gamma $,dp) and $^{4}$He($\gamma $,tp) reactions are compared with the model predictions of Laget$^{2}$ to throw further light on three-body mechanisms and reaffirm their importance. The angular distribution for $^{4}$He($\gamma $,dd) shows no evidence for dipole reactions and the breaking of isospin symmetry, in contrast with earlier results at lower energies. And selecting only those $^{3}$He($\gamma $,pp)n events where the neutron is a spectator enables us to study the two-body photodisintegration of $^{2}$He, with surprising results, in preparation for an upcoming experiment$^{3}$ on hard-pp quark-exchange processes.\newline \newline $^{1}$ S. Niccolai \textit{et al}., Phys. Rev. C \textbf{70}, 064003 (2004)\newline $^{2}$ J-M. Laget, Pr. Comm. (2004)\newline $^{3}$ R. Gilman \textit{et al}., JLab Expt. E03-101 (2003)