Direct correlation between the near-proton-emission threshold resonance in $^{11}$B and the branching ratio of beta-delayed proton emission from $^{11}$Be

Abstract

Background: Beta-delayed proton emission from neutron halo nuclei $^{11}$Be represents a rare decay process. The existence of the narrow resonance near the proton-emission threshold in $^{11}$B explains its unexpectedly high probability. However, the accurate value of the branching ratio remains challenging to determine. Purpose: We aim to provide a microscopic potential model to determine the branching ratio for beta-delayed proton emission from $^{11}$Be. We focus on quantifying the influence of the narrow resonance near the proton emission threshold on the result of the branching ratio. Method: We employ the Skyrme Hartree-Fock calculation within the potential model to obtain the branching ratio. We derive the single-particle potentials for the halo neutron and the emitting proton from the Skyrme Hartree-Fock calculation with minimal adjustment. As the resonance position is tightly linked to the potential depth, we can demonstrate quantitatively how variations in its location impact the outcome. Result: Slight variations in the resonance position significantly impact the branching ratio, with the upper limit reaching the order of $10^{-5}$. Conclusion: Experimental determination of the resonance energy, particularly whether it lies below $200$ keV, is crucial for determining the value of the branching ratio.