Improved limits on Fierz interference using asymmetry measurements from the Ultracold Neutron Asymmetry (UCNA) experiment

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19 Scopus citations


The Ultracold Neutron Asymmetry (UCNA) experiment was designed to measure the β-decay asymmetry parameter, A0, for free neutron decay. In the experiment, polarized ultracold neutrons are transported into a decay trap, and their β-decay electrons are detected with ≈4π acceptance into two detector packages which provide position and energy reconstruction. The experiment also has sensitivity to bn, the Fierz interference term in the neutron β-decay rate. In this work, we determine bn from the energy dependence of A0 using the data taken during the UCNA 2011-2013 run. In addition, we present the same type of analysis using the earlier 2010 A dataset. Motivated by improved statistics and comparable systematic errors compared to the 2010 data-taking run, we present a new bn measurement using the weighted average of our asymmetry dataset fits, to obtain bn=0.066±0.041stat±0.024syst which corresponds to a limit of -0.012<bn<0.144 at the 90% confidence level.

Original languageEnglish
Article number035503
JournalPhysical Review C
Issue number3
StatePublished - Mar 2020

Bibliographical note

Funding Information:
This work is supported in part by the U.S. Department of Energy, Office of Nuclear Physics (DE-FG02-08ER41557, DE-SC0014622, DE-FG02-97ER41042) and the National Science Foundation (1002814, 1005233, 1205977, 1306997, 1307426, 1506459, 1615153, 1812340, and 1914133). Furthermore, we gratefully acknowledge the support of the LDRD program (20110043DR), and the help of those at the Accelerator Operations and Technology division at Los Alamos National Laboratory.

Publisher Copyright:
© 2020 American Physical Society.

ASJC Scopus subject areas

  • Nuclear and High Energy Physics


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