Two-nucleon knock-out investigated with the semi-exclusive 12C(e, e′p) reaction

The 12C(e, e′p) reaction has been studied in the dip region, at an energy transfer ω = 212 MeV and a three-momentum transfer |q| = 270 MeV/c. The data cover a missing energy range 0–180 MeV and include missing momenta up to 750 MeV/c. The cross sections, measured at various angles between the detected proton and q, show a clear signature for two-nucleon knock-out. At large angles, the measured strength can mainly be attributed to the coupling of the virtual photon to pion exchange currents and intermediate Δ-excitation. The data at small angles cannot be explained by these mechanisms alone. It is suggested that additional strength originates from the emission of a correlated nucleon pair.