Abstract
The standard model predicts that, in addition to a proton, an electron, and an antineutrino, a continuous spectrum of photons is emitted in the β decay of the free neutron. We report on the RDK II experiment which measured the photon spectrum using two different detector arrays. An annular array of bismuth germanium oxide scintillators detected photons from 14 to 782 keV. The spectral shape was consistent with theory, and we determined a branching ratio of 0.00335±0.00005[stat]±0.00015[syst]. A second detector array of large area avalanche photodiodes directly detected photons from 0.4 to 14 keV. For this array, the spectral shape was consistent with theory, and the branching ratio was determined to be 0.00582±0.00023[stat]±0.00062[syst]. We report the first precision test of the shape of the photon energy spectrum from neutron radiative decay and a substantially improved determination of the branching ratio over a broad range of photon energies.
| Original language | English |
|---|---|
| Article number | 242501 |
| Journal | Physical Review Letters |
| Volume | 116 |
| Issue number | 24 |
| DOIs | |
| State | Published - Jun 14 2016 |
Bibliographical note
Publisher Copyright:© 2016 American Physical Society.
Funding
We thank Changbo Fu for his initial simulation work and David Winogradoff for his calibration studies. We additionally thank R. Farrell for numerous discussions about APD operation and their properties. This research was supported in part through computational resources and services provided by Advanced Research Computing at the University of Michigan, Ann Arbor. We acknowledge the support of the National Institute of Standards and Technology, U.S. Department of Commerce, in providing the neutron facilities used in this work. This research was made possible in part by support from the National Science Foundation (Grants No.PHY-0969654, No.PHY-1205266, No.PHY-1205393, No.PHY-1306547, and No.PHY-1505196) and the U.S. Department of Energy (Grant No.DE-FG02-96ER40989 and an interagency agreement).
| Funders | Funder number |
|---|---|
| National Science Foundation (NSF) | 1306547, 1205393, 0969654, 1505196, 1506021, 1205266 |
| Michigan State University-U.S. Department of Energy (MSU-DOE) Plant Research Laboratory | |
| National Institute of Standards and Technology | |
| U.S. Department of Commerce |
ASJC Scopus subject areas
- General Physics and Astronomy