Bulletin of the American Physical Society
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado
Session H14: Mini-Symposium:The Neutron Lifetime Anomaly - possible explanations
10:45 AM–12:21 PM,
Sunday, April 14, 2019
Sheraton Room: Plaza Court 3
Sponsoring Unit: DNP
Chair: Chris Wrede, Michigan State University
Abstract: H14.00003 : Exotic decay modes in Be-11
11:33 AM–11:45 AM
Wolfgang J Mittig
ATTPC and S1845 collaborations
In a recent letter  a novel explanation was proposed for the so-called neutron lifetime anomaly. To explain the difference in the rate of disappearing neutrons and appearing protons, they suggested that neutrons could decay into dark sector particles ~1% of the time. In , they also calculated that a few selected nuclei, as Be-11, haven an open energy window for this hypothetical dark decay.
Be-11 is the only isotope for which indirect and ambiguous evidence of beta-delayed proton emission decay exists . They implanted Be-11 in a foil and then, using mass spectroscopy, measured the amount of Be-10 created, thus measuring a combination of all possible decay modes leading to Be-10.
We performed an experiment at TRIUMF using the prototype Active Target Time Projection Chamber (pATTPC) and the high purity of the ISAC Be beams to directly observe the beta-p decay channel for the first time. The use of the pATTPC allowed for the unambiguous observation of the proton emission. We will present preliminary results on the measured branching ratio, where any difference with that measured in  would hint to the presence of a dark decay branch in Be-11.
 B. Fornal and B. Grinstein. Phys. Rev. Lett., 120:191801 (2018)
 K. Riisager, et al. Physics Letters B, 732:305 (2014)
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