The C-12(gamma,NN) reaction studied over a wide kinematic range - art. no.014616

The C-12( gamma,np) and C-12( gamma,pp) reactions have been studied using t he Glasgow photon tagging spectrometer at the Mainz MAMI electron microtron for E gamma = 150-700 MeV over a kinematic range which extends well beyond the approximately back-to-back detector arrangements of previous work. For C-12(gamma,np) the general trends of the missing energy distributions are reproduced over a wide range of kinematics and photon energies by the theor y developed by the Valencia group. The corresponding C-12(gamma,PP) channel is overestimated by a factor of similar to 3. Detailed comparisons of the experimental data with a Monte Carlo simulation of the direct 2N knockout p rocess provide the first evidence above the Delta resonance for direct 2N k nockout and show that this process dominates the C-12(gamma,np) reaction at low missing energies up to E gamma similar to 700 MeV. The C-12(gamma,pp) reaction is somewhat less well described by the Monte Carlo simulation. A p ossible explanation of the observed discrepancies within a direct 2N framew ork is presented. At high recoil momenta both 2N reaction channels exhibit an excess yield compared to the Monte Carlo prediction of direct 2N knockou t. The excess yield in this region is compared with the predicted effects o f short-range correlations and with the predicted contributions due to othe r reaction mechanisms.