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The neutron lifetime anomaly: analysis of charge exchange and molecular reactions in a proton trap

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Abstract

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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Data Availability Statement

This manuscript has no associated data or the data will not be deposited. [Authors' comment: Data used are referenced or the source is acknowledged. Data generated are in the manuscript.]

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Acknowledgements

We thank John Morse for many informative discussions and permission to reproduce Fig. 1a and b from his 1980 D. Phil thesis (University of Sussex), along with the Linear Regression data listed in Table 2. Extensive assistance of staff at the NIST Research Library, especially Alan Olson, is very gratefully acknowledged. We also thank Xavier Urbain for communications on the 2013 H2 charge exchange data and Dario De Fazio for communications on the 2012 helium + H2+ molecular reaction analysis at low energies. We thank Michael Weinrich for helpful comments on the manuscript.

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Authors and Affiliations

  1. Department of Physics and Astronomy, University of Sussex, Falmer, Brighton, BN1 9QH, UK

    J. Byrne

  2. NIST Center for Neutron Research, Gaithersburg, MD, 20899, USA

    D. L. Worcester

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  1. J. Byrne
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Correspondence to D. L. Worcester.

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Communicated by Klaus Blaum.

Dedicated to the memory of the late Norman F. Ramsey.

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Byrne, J., Worcester, D.L. The neutron lifetime anomaly: analysis of charge exchange and molecular reactions in a proton trap. Eur. Phys. J. A 58, 151 (2022). https://doi.org/10.1140/epja/s10050-022-00786-8

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