One- and two-nucleon transfer in the ${}^{28}\mathrm{Si}{+}^{68}$Zn system at energies below the Coulomb barrier

Excitation functions for one- and two-nucleon transfer in ${}^{28}$Si + ${}^{68}$Zn system have been measured at energies below the Coulomb barrier. The experiment was carried out by detecting the forward recoiling targetlike nuclei using the recoil mass separator, HIRA. With a pulsed beam, the time-of-flight of the recoils was measured and used to resolve the $M/q$ ambiguity. This enabled the determination of the two-nucleon transfer yields. The role of one- and two-nucleon transfer in the sub-barrier fusion cross-section enhancement has been investigated. It turns out that the coupling of the positive $Q$-value two-neutron transfer channel results in a significant contribution to the enhancement. Coupling to both the transfer and the inelastic channels is able to explain the observed enhancement.