Erratum: Direct Observation of Proton Emission in Be11 [Phys. Rev. Lett. 123 , 082501 (2019)]

Abstract

In the Letter, we presented the first direct observation of the elusive β −-delayed proton emission (β − p þ) in 11 Be using a time projection chamber. There is an error in the extracted logðftÞ, which should read 2.8(4). The corrected logðftÞ value does not affect the conclusions presented in the Letter, since it was only used to assert the allowed character of the transition, a conclusion that is not changed. We would like to point out that, assuming a pure Gamow-Teller (GT) transition, it yields BðGTÞ ¼ 5.5 þ8.3 −3.3 , thus, including the BðGTÞ < 3 limit for a single neutron decay within one sigma. It should be noted that, due to the small energy window, the uncertainty in the resonance energy amounts to nearly 75% of the error budget for the logðftÞ value. Thus, a more precise measurement of the resonance energy could bring the B(GT) to within theoretical limits without significantly affecting the measured branching ratio.

Beta decay of halo nuclei

“…The next wellestablished resonance is at 10.6 MeV with spin-parity 5/2 − and is also clearly observed in the above channels [63,66]. The triton branch has a branching ratio in the range (1 − 2) • 10 −4 , the lower limit comes from direct detection in experiments where not all events may have been observed [64,67] and the upper limit from an indirect detection of the daughter nucleus 8 Li [74]. The total B(GT ) strength identified so far in this energy range is around 2.…”

“…8 He: The structure of this nucleus is not completely settled, it is sometimes considered a halo nucleus, sometimes as having a sizable neutron skin. The latest experiment on its decay [26] identify four transitions to excited 1 + states in 8 Li with the highest one at around 9.3 MeV giving beta-delayed tritons and having a B(GT ) that according to R-matrix fits [16] is large, in the range 4-5. The neutron branch is also significant, but more work is needed to settle the interpretation of it.…”

“…The neutron branch is also significant, but more work is needed to settle the interpretation of it. Few-body theoretical calculations [44,107] of the decay have also been made and indicated sensitivity to the detailed structure of 8 He, but there is so far no clear indications for halo signatures in the decay. More experimental data would be welcome.…”

“…Both states are broad, so the most recent experiment [90] employed an R-matrix analysis to derive a total B(GT ) strength of 1.0(2). The Q-value for beta-delayed proton decay is very small, but observation of this branch would provide a parallel to the beta-delayed deuteron decays of two-neutron halos and several experiments have therefore been carried out [8,30,96,98]. An-Fig.…”

“…other motivation came from the suggestion that the neutron could decay to a dark particle [39] in which case one may observe 11 Be decay into 10 Be and a dark (and invisible) particle [86]. This is relevant if the experiment observes 10 Be rather than the proton, as is the case in all experiments so far except [8]. A first indication [96] for the presence of 10 Be could not be confirmed [98] and led instead to an upper limit of 2.2 • 10 −6 of the β p branch.…”