Transparency of {sup 12}C for protons

Existing cross-section data for 1p-shell knockout in the reaction {sup 12}C(e,e{sup '}p){sup 11}B --as obtained under different kinematic conditions--are shown to be mutually 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 {sup 12}C(e,e{sup '}p){sup 11}B data has yielded precise values of the spectroscopic factor for 1p-shell and 1s-shell knockout from {sup 12}C. These values have been used to evaluate the transparency of the {sup 12}C nucleus for 1p-shell and 1s-shell protons separately on the basis of recent high-energy {sup 12}C(e,e{sup '}p){sup 11}B data taken at a four-momentum transfer squared Q{sup 2} of 1.1 (GeV/c){sup 2}. As the resulting average value of the nuclear transparency, 0.81{+-}0.04, is considerably higher than the value obtained from previous analyses and theoretical estimates, the high Q{sup 2} data were used instead for an independent determination of the spectroscopic strength for 1p+1s knockout. Combining these results with the low Q{sup 2} data the spectroscopic factors appear to be momentum-transfer dependent. Possible explanations of these surprising results in terms of reaction-mechanism effects or a possible breakdown of the quasiparticle concept at high Q{supmore » 2} are discussed as well. (c) 2000 The American Physical Society.« less