Quasielastic knockout of alpha clusters by intermediate energy protons: Signatures of virtually excited states

Abstract

The long-standing problem of experimental signatures for clustering effects in light nuclei is discussed for the conditions corresponding to a recent experiment. The specific reaction ${}^{12}\mathrm{C}{(p,p}^{\ensuremath{'}}\ensuremath{\alpha}{)}^{8}\mathrm{Be}$ at incident proton energy 300 MeV and fixed proton and alpha-particle angles near the quasielastic peak is discussed. The Glauber approximation with a simple parametrization of the elementary nucleon-nucleon amplitude is used for calculating the cross section. The main emphasis is on the existence of virtually excited cluster configurations and their manifestation in experimental observables. The shell model wave function of the ${}^{12}\mathrm{C}$ ground state is used to extract the weights of excited cluster components and to calculate their contributions to the cross section. The presence of several excited components and their complicated interference influence the shape and the height of the quasielastic peak; the change can reach an order of magnitude. It is shown that the cross section for cluster emission with the excitation of ${}^{8}\mathrm{Be}$ into the first excited ${2}^{+}$ state is small as compared to the process leaving ${}^{8}\mathrm{Be}$ in its ground state.