First measurement of the reaction helium-3(photon,proton -proton)neutron

Differential cross sections for the {dollar}\sp3{dollar}He({dollar}\gamma{dollar},pp)n reaction were measured with a bremsstrahlung beam for kinematics selected in the quasi-free two-nucleon region with neutron recoil q{dollar}\sb{lcub}\rm n{rcub}\approx{dollar} 0. Five photon energy points were taken between 200 and 440 MeV. The two proton detectors were positioned in such a way that the angle of one proton, in the CM of the pp pair, relative to the photon direction is 75{dollar}\sp\circ{dollar}. The data confirm the predicted quenching of the cross section. In the photon energy region from 310 to 440 MeV the data are in agreement with a theoretical prediction based on a diagrammatic description of the process. at lower energies (200 to 310 MeV) the data are about 40% to 70% higher than the predictions. However the shape of the proton momentum spectrum is reproduced when three body mechanisms are included