QUASI-ELASTIC KNOCKOUT OF ALPHA-CLUSTER BY INTERMEDIATE-ENERGY PROTONS - SIGNATURES OF VIRTUALLY EXCITED-STATES

The long-standing problem of experimental signatures for clustering ef fects in light nuclei is discussed for the conditions corresponding to a recent experiment. The specific reaction C-12(p,p'alpha)Be-8 at inc ident proton energy 300 MeV and fixed proton and alpha-particle angles near the quasielastic peak is discussed. The Glauber approximation wi th a simple parametrization of the elementary nucleon-nucleon amplitud e is used for calculating the cross section. The main emphasis is on t he existence of virtually excited cluster configurations and their man ifestation in experimental observables. The shell model wave function of the C-12 ground state is used to extract the weights of excited clu ster components and to calculate their contributions to the cross sect ion. The presence of several excited components and their complicated interference influence the shape and the height of the quasielastic pe ak; the change can reach an order of magnitude. It is shown that the c ross section for cluster emission with the excitation of Be-8 into the first excited 2(+) state is small as compared to the process leaving Be-8 in its ground state.