Transparency of C-12 for protons - art. no. 064325

Existing cross-section data for 1p-shell knockout in the reaction C-12(e,e' p)B-11 -as obtained under different kinematic conditions-are shown to be m utually consistent, apart from a recent measurement performed in Mainz. New data have been collected at the Amsterdam Pulse Stretcher that confirm the normalization of the older measurements. An analysis of the world's C-12(e ,e' p)B-11 data has yielded precise values of the spectroscopic factor for 1p-shell and 1s-shell knockout from C-12. These values have been used to ev aluate the transparency of the C-12 nucleus for 1p-shell and 1s-shell proto ns separately on the basis of recent high-energy C-12(e,e' p)B-11 data take n at a four-momentum transfer squared Q(2) of 1.1 (GeV/c)(2). As the result ing average Value of the nuclear transparency, 0.81+/-0.04, is considerably higher than the value obtained from previous analyses and theoretical esti mates, the high Q(2) data were used instead for an independent determinatio n of the spectroscopic strength for 1p + 1s knockout. Combining these resul ts with the low Q(2) data the spectroscopic factors appear to be momentum-t ransfer dependent. Possible explanations of these surprising results in ter ms of reaction-mechanism effects or a possible breakdown of the quasipartic le concept at high Q(2) are discussed as well.