Hard Photo-disintegration of proton pairs in $^3$He

Hard deuteron photo-disintegration has been investigated for 20 years, as its cross sections follow the constituent counting rules and it provides insight into the interplay between hadronic and quark-gluon degrees of freedom in high-momentum transfer exclusive reactions. We have now measured for the first time hard $pp$-pair disintegration in the reaction $\gamma \, ^3 {\rm He} \to $pp$ + n$, using kinematics corresponding to a spectator neutron. Clues to the underlying physics can be found in the comparison of our measurements with deuteron photo-disintegration, the energy dependence of the cross sections at 90$^{\circ}$ c.m., the $\alpha_n$ distribution, and the angular distribution.