Multichannel experimental and theoretical constraints for the Cd 116 (Ne 20, F 20) in 116 charge exchange reaction at 306 MeV

Background: Charge-exchange (CE) reactions offer a major opportunity to excite nuclear isovector modes, providing important clues about the nuclear interaction in the medium. Moreover, double charge-exchange reactions are proving to be a tempting tool to access nuclear transition matrix elements (NMEs) related to double beta-decay processes. The latter are also of crucial importance to extract neutrino properties from the half-life of the hypothetical neutrinoless double beta decay and to search for physics beyond the standard model. Purpose: Through a multichannel experimental analysis and a consistent theoretical approach of the Cd116(Ne20,F20)In116 single charge-exchange (SCE) reaction at 306 MeV, we aim at disentangling from the experimental cross section the contribution of the competing mechanisms associated with second- or higher-order sequential transfer and/or inelastic processes. Methods: We measured excitation energy spectra and absolute cross sections for elastic + inelastic, one-proton transfer and SCE channels by using the MAGNEX large acceptance magnetic spectrometer to detect the ejectiles. For the first two channels, we also extracted the experimental cross-section angular distributions. The experimental data are compared with theoretical predictions obtained by performing two-step distorted-wave Born approximation and coupled reaction channel calculations. We employ spectroscopic amplitudes for single-particle transitions derived within a large-scale shell-model approach and different optical potentials for modeling the initial- and the final-state interactions. Results: The present study significantly mitigates the possible model dependence existing in the description of these complex reaction mechanisms thanks to the satisfactory reproduction of several channels at once. In particular, our work demonstrates that the two-step transfer mechanisms produce a non-negligible contribution to the total cross section of the Cd116(Ne20,F20)In116 reaction channel, although a relevant fraction is still missing, being ascribable to the direct SCE mechanism, which is not addressed here. Conclusions: Our analysis provides a careful estimation of the sequential transfer processes which are competing with the direct SCE mechanism for the heavy ion reaction under investigation. The study suggests that the direct SCE should play an important role among the mechanisms populating the final channel. Nevertheless, the analysis of the higher-order processes considered here is mandatory to isolate the direct SCE process contribution and approach structure information on the corresponding NME from the reaction cross section. The description of the latter process and the competition between the two mechanisms deserves further investigation.