Transparency of12Cfor protons

Existing cross-section data for $1p$-shell knockout in the reaction ${}^{12}\mathrm{C}{(e,e}^{\prime }{p)}^{11}\mathrm{B}$ —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 ${}^{12}\mathrm{C}{(e,e}^{\prime }{p)}^{11}\mathrm{B}$ data has yielded precise values of the spectroscopic factor for $1p$-shell and $1s$-shell knockout from ${}^{12}\mathrm{C}.$ These values have been used to evaluate the transparency of the ${}^{12}\mathrm{C}$ nucleus for $1p$-shell and $1s$-shell protons separately on the basis of recent high-energy ${}^{12}\mathrm{C}{(e,e}^{\prime }{p)}^{11}\mathrm{B}$ data taken at a four-momentum transfer squared $Q^2$ of 1.1 $(\mathrm{GeV}{/c)}^2.$ As the resulting average value of the nuclear transparency, $0.81\pm 0.04,$ is considerably higher than the value obtained from previous analyses and theoretical estimates, the high $Q^2$ data were used instead for an independent determination of the spectroscopic strength for $1p+1s$ knockout. Combining these results with the low $Q^2$ 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 $Q^2$ are discussed as well.