Measurement of the Spectral Shape of the β-Decay of Xe 137 to the Ground State of Cs 137 in EXO-200 and Comparison with Theory

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We report on a comparison between the theoretically predicted and experimentally measured spectra of the first-forbidden nonunique β-decay transition Xe137(7/2-)→Cs137(7/2+). The experimental data were acquired by the EXO-200 experiment during a deployment of an AmBe neutron source. The ultralow background environment of EXO-200, together with dedicated source deployment and analysis procedures, allowed for collection of a pure sample of the decays, with an estimated signal to background ratio of more than 99 to 1 in the energy range from 1075 to 4175 keV. In addition to providing a rare and accurate measurement of the first-forbidden nonunique β-decay shape, this work constitutes a novel test of the calculated electron spectral shapes in the context of the reactor antineutrino anomaly and spectral bump.

Original languageEnglish
Article number232502
JournalPhysical Review Letters
Issue number23
StatePublished - Jun 12 2020

Bibliographical note

Funding Information:
EXO-200 is supported by DOE and NSF in the United States, NSERC in Canada, IBS in Korea, RFBR (18-02-00550) in Russia, DFG in Germany, and CAS and ISTCP in China. EXO-200 data analysis and simulation uses resources of the National Energy Research Scientific Computing Center (NERSC). This work has been partially supported by the Academy of Finland under the Academy Project No. 318043. J. K. acknowledges the financial support from the Jenny and Antti Wihuri Foundation. We gratefully acknowledge the KARMEN collaboration for supplying the cosmic ray veto detectors, and the WIPP for their hospitality.

Publisher Copyright:
© 2020 American Physical Society.

ASJC Scopus subject areas

  • Physics and Astronomy (all)


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