Probing Pair Correlations in ⁷⁶Ge via Two-Proton Exchange Cross-Section Measurements

Cross-section measurements for the (³He, n) reaction on ^74,76Ge have been performed at laboratory beam energies of 15 and 21 MeV for reaction angles from 0° to 18°. These data test the validity of the Bardeen-Cooper-Schrieffer (BCS) approximation for the wavefunctions of the ground states of the initial and final 0⁺ nuclei used in QRPA calculations of nuclear matrix elements for neutrinoless double beta (0νββ) decay of ⁷⁶Ge [1].  The measured strength for transfer to the first 0⁺ excited state was less than 13% of the transfer to the ground state for both nuclei, suggesting that using the BCS approximation to describe the ⁷⁶Se ground state in QRPA 0νββ calculations is valid. This result is consistent with recent (³He, n) cross-section measurements on these nuclei [1]. Fits to the cross-section angular distributions for transfer to the ground state using the DWBA code FRESCO provide information about the reaction mechanism and are sensitive to the optical model potential used in the calculations. The experimental method and results will be presented.

[1] A. Roberts et al., Phys. Rev C 87, 051305(R) (2013).