$β^-{\rm p}$ and $β^-α$ decay of the $^{11}$Be neutron halo ground state

Abstract

Beta-delayed proton emission from the neutron halo ground state of 11 Be raised much attention due to the unusually high decay rate. It was argued that this may be due to the existence of a resonance just above the proton decay threshold. In this Letter, we use the lenses of real-energy continuum shell model to describe several observables including the Gamow-Teller rates for the β − -delayed α and proton decays, and argue that, within our model, the large β − p branching ratio cannot be reconciled with other data.

Beta decay of halo nuclei

“…The first results [19,30] gave branching ratios around 3 • 10 −8 , but higher values (up to around 10 −5 ) may be obtained if a resonance is present in the Q-window for the decay [95,96], a conclusion verified by now via several different model calculations [8,37,121]. A convincing theoretical prediction must reproduce both the β α and β p branches, as attempted with the shell model embedded in the continuum [77,78]. It is clearly of interest to clarify the beta-delayed proton decay experimentally due to the considerable theoretical and conceptual interest.…”

Neutron Stars with Baryon Number Violation, Probing Dark Sectors

“…It has been noted that a new resonance state could explain the large branching ratio, and this appears to be possible theoretically, both from direct study of the resonance properties [173] and from a study within halo-nucleus effective field theory [174]. Without a resonance, the decay rate would be very challenging to explain [175,176]. These studies constrain the size of a possible dark decay of the neutron in reference to the neutron lifetime anomaly, but have little impact on the broader possibilities we consider here.…”

Ab initio calculation of the $β$-decay from $^{11}$Be to a p${+}^{10}$Be resonance

“…The authors of Ref. [8], using a shell model embedded in the continuum (SMEC), conclude that the branching ratio of β-delayed α emission, the predicted resonance width, and the observed β-delayed proton emission in Ref. [6] can not be reconciled within their calculations.…”