Regular Article - Experimental Physics
The neutron lifetime anomaly: analysis of charge exchange and molecular reactions in a proton trap
Department of Physics and Astronomy, University of Sussex, Falmer, BN1 9QH, Brighton, UK
2 NIST Center for Neutron Research, 20899, Gaithersburg, MD, USA
Accepted: 3 July 2022
Published online: 16 August 2022
Current values of the neutron lifetime, determined by two entirely distinct measurement techniques of comparable precision, differ to a statistically significant degree, a result which has become known as the neutron lifetime anomaly. In a previous publication we have shown that the discrepancy can be resolved by taking account of electron transfer charge exchange reactions between residual gases and final state protons stored in a quasi-Penning trap. In this article we analyze unique experimental data obtained during the course of the first published neutron lifetime measurement that used a proton trap. These data employed trapping times greater by a factor of a thousand than became conventional in later experiments. The data show that significant event losses occur, probably due to residual gas other than molecular hydrogen or helium. Additionally, the molecular ion H2+ produced by charge exchange in H2 undergoes secondary molecular reactions, producing the molecular ion H3+ and the ion HeH+ which is also produced by secondary reactions in helium. These ions could result in event losses depending on the energy and time-of-flight acceptance windows. Energy losses are evaluated and ionic compositions are quantitively assessed as functions of trapping time and residual gas density to account for an energy spectrum obtained using a silicon surface barrier detector. The spectrum is strongly influenced by charge exchange, secondary molecular reactions and backscattering in the detector dead layer.
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