Alpha-cluster knockout in the O-16(e,e 'alpha)C-12 reaction

Abstract The knockout of α -clusters induced by electrons has been used to study four-nucleon correlations in 16 O. For the transition to the ground state of 12 C the (e,e′ α ) cross section has been measured for three values of the momentum transfer and four values of the missing momentum. The momentum-transfer dependence gives evidence for a quasi-elastic α -knockout mechanism. The shape of the measured missing-momentum distribution is reasonably well described by shell-model and cluster-model calculations, but the theoretical curves overshoot the data by a factor three to four.