Gamma-delayed deuteron emission of the [formula omitted] halo state

Abstract

M1 transitions from the Li 6 ( 0 + ; T = 1 ) state at 3.563 MeV to the Li 6 ( 1 + ) ground state and to the α + d continuum are studied in a three-body model. The bound states are described as an α + n + p system in hyperspherical coordinates on a Lagrange mesh. The ground-state magnetic moment and the gamma width of the Li 6 ( 0 + ) resonance are well reproduced. The halo-like structure of the Li 6 ( 0 + ) resonance is confirmed and is probed by the M1 transition probability to the α + d continuum. The spectrum is sensitive to the description of the α + d phase shifts. The corresponding gamma width is around 1.0 meV, with optimal potentials. Charge symmetry is analyzed through a comparison with the β-delayed deuteron spectrum of 6He. In 6He, a nearly perfect cancellation effect between short-range and halo contributions was found. A similar analysis for the Li 6 ( 0 + ; T = 1 ) γ decay is performed; it shows that charge-symmetry breaking at large distances, due to the different binding energies and to different charges, reduces this effect. The present branching ratio Γ γ ( 0 + → α + d ) / Γ γ ( 0 + → 1 + ) ≈ 1.3 × 10 −4 should be observable with current experimental facilities.