OMPs for the ⁶ He+ ²⁰⁹ Bi halo system from a ²⁰⁸ Pb( ⁷Li, ⁶ He) ²⁰⁹Bi reaction analysis

Angular distributions of transfer reaction ²⁰⁸Pb(⁷Li,⁶He)²⁰⁹Bi were measured at Elab(⁷Li)= 21.2, 24.3, 25.67 and 28.55 MeV. By fitting the experimental data with the theoretical frameworks of Distorted Wave Born Approximation (DWBA), the optical model parameters of the halo nuclear system ⁶He+²⁰⁹Bi were extracted. The breakup threshold anomaly (BTA) was observed clearly in the imaginary potential, and a further decreasing trend in the deep sub-barrier region was observed for the first time in a halo system. Furthermore, the dispersion relation is found of no use to describe the connection between the real and imaginary parts