Coupled-channels analyses for ^9,11Li + ²⁰⁸Pb fusion reactions with multi-neutron transfer couplings

We discuss the role of two-neutron transfer processes in the fusion reaction of the ^9,11Li + ²⁰⁸Pb systems. We first analyze the ⁹Li + ²⁰⁸Pb reaction by taking into account the coupling to the ⁷Li + ²¹⁰Pb channel. To this end, we assume that two neutrons are directly transferred to a single effective channel in ²¹⁰Pb and solve the coupled-channels equations with the two channels. By adjusting the coupling strength and the effective Q-value, we successfully reproduce the experimental fusion cross sections for this system. We then analyze the ¹¹Li + ²⁰⁸Pb reaction in a similar manner, that is, by taking into account three effective channels with ¹¹Li + ²⁰⁸Pb, ⁹Li + ²¹⁰Pb, and ⁷Li + ²¹²Pb partitions. In order to take into account the halo structure of the ¹¹Li nucleus, we construct the potential between ¹¹Li and ²⁰⁸Pb with a double folding procedure, while we employ a Woods–Saxon type potential with the global Akyüz–Winther parameters for the other channels. Our calculation indicates that the multiple two-neutron transfer process plays a crucial role in the ¹¹Li + ²⁰⁸Pb fusion reaction at energies around the Coulomb barrier.