Analysis of pairing correlations in neutron transfer reactions and comparison to the constrained molecular dynamics model

The transfer yields mass spectra were measured in ${}^{11}\mathrm{B},{}^{12,13}\mathrm{C},{}^{28}\mathrm{Si}\left({}^{18}\mathrm{O},{}^{17}\mathrm{O}\right)$ and ${}^{11}\mathrm{B},{}^{12,13}\mathrm{C},{}^{28}\mathrm{Si}\left({}^{18}\mathrm{O},{}^{16}\mathrm{O}\right)$ reactions at 84 MeV. The two-neutron transfer (2NT) and the one-neutron transfer (1NT) cross sections were extracted for all the systems. The 2NT cross section is found comparable to the 1NT one and remarkably larger than that predicted assuming no correlations among the two transferred nucleons and only natural parity states are populated via the $\left({}^{18}\mathrm{O},{}^{16}\mathrm{O}\right)$ two-neutron transfer reaction. Calculations based on the constrained molecular dynamics model show that such behavior is uniquely a consequence of neutron pairing correlations in the ${}^{18}\mathrm{O}$ ground state.

Figure 1

Examples of the excitation energy spectra for the ${}^{13}\mathrm{C}\left({}^{18}\mathrm{O},{}^{16}\mathrm{O}\right){}^{15}\mathrm{C}$ and ${}^{13}\mathrm{C}\left({}^{18}\mathrm{O},{}^{17}\mathrm{O}\right){}^{14}\mathrm{C}$ reactions at 84 MeV incident energy and $7^{\circ }<{\theta }_{\mathrm{lab}}<{18}^{\circ }$. The grey area corresponds to the model for the background subtraction (see text). The blue dashed line and the red dashed-dotted lines correspond to the three-body and four-body continuum channels, which open above $S_{\mathrm{n}}$ and $S_{2\mathrm{n}}$, respectively.

Figure 2

$R={\sigma }_{1\mathrm{NT}}/{\sigma }_{2\mathrm{NT}}$ for the considered targets. The squares refer to the experimental data, while the circles and the triangles refer to the CoMD and CoMD+NN calculations respectively