Multi-mechanisms in proton-induced nucleon removal from 14O at 94 MeV/nucleon

"The one-nucleon removal reaction from nuclei is a strong tool to investigate the single-particle structure. From the measurement of the residual nucleus, the orbital angular momentum of the removed nucleon can be determined. In the last decades, systematic studies on the quenching of the single-particle strength and the parallel momentum distribution of the removed nucleons have been performed. Asymmetric momentum distributions and discrepancies between measured cross sections and predictions, in particular for the deeply-bound nucleons, demonstrated, that the reaction mechanism needs to be further understood. From theoretical studies with a proton target at 100 MeV/nucleon the asymmetric distribution is attributed to stem from the interaction of the outgoing particles with the residual core nucleus. A confirmation of these theoretical results would emphasize the significance of the final state interactions. However, most of the experimental data was taken with light-ion targets and there is no data with proton targets in this incident-energy region.

This is why the one-nucleon removal reaction from 14O at 94 MeV/nucleon from a hydrogen target was performed. The nucleus 14O has a large asymmetry in proton and neutron separation energies Sn - Sp = 18.55(1) MeV. The 14O secondary beam was impinged on a 2.4 mm thick solid hydrogen target. The resulting fragments were measured with the SAMURAI spectrometer. In particular, the one-nucleon removal residues 13O and 13N are of interest. Their measured inclusive cross sections and parallel momentum distributions (PMDs) are compared to theoretical calculations. Inelastic scattering, the distorted-wave impulse approximation and quantum transfer to the continuum are considered for theoretical calculations. Shell-model spectroscopic factors are applied for the comparison with the experimental data. A symmetric shape is observed for the proton removal channel, for which the (p,2p) knockout and the (p,p') inelastic channel are found contributing almost equally. The neutron removal channel exhibits a strongly asymmetric PMD, which is reproduced well by combining the results from (p,pn) knockout and (p,d) transfer. The quenching of the single-particle strength is quantified by the reduction factor Rs, which is defined by ratio of the experimental to the theoretical cross section. The reduction factors Rs are obtained and are compared to heavy-ion induced knockout and transfer reaction results. The results of this work show that the proton-induced nucleon removal from rare isotopes at energies of ~100 MeV/nucleon originates in several reaction mechanisms, including quasi-free scattering, inelastic scattering and transfer."