First Precision Measurement of the Parity Violating Asymmetry in Cold Neutron Capture on He 3

M. T. Gericke, S. Baeßler, L. Barrón-Palos, N. Birge, J. D. Bowman, J. Calarco, V. Cianciolo, C. E. Coppola, C. B. Crawford, N. Fomin, I. Garishvili, G. L. Greene, G. M. Hale, J. Hamblen, C. Hayes, E. Iverson, M. L. Kabir, M. McCrea, E. Plemons, A. Ramírez-MoralesP. E. Mueller, I. Novikov, S. Penttila, E. M. Scott, J. Watts, C. Wickersham

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


We report the first precision measurement of the parity-violating asymmetry in the direction of proton momentum with respect to the neutron spin, in the reaction He3(n,p)3H, using the capture of polarized cold neutrons in an unpolarized active He3 target. The asymmetry is a result of the weak interaction between nucleons, which remains one of the least well-understood aspects of electroweak theory. The measurement provides an important benchmark for modern effective field theory and potential model calculations. Measurements like this are necessary to determine the spin-isospin structure of the hadronic weak interaction. Our asymmetry result is APV=[1.55±0.97(stat)±0.24(sys)]×10-8, which has the smallest uncertainty of any hadronic parity-violating asymmetry measurement so far.

Original languageEnglish
Article number131803
JournalPhysical Review Letters
Issue number13
StatePublished - Sep 2020

Bibliographical note

Funding Information:
We gratefully acknowledge the support of the U.S. Department of Energy Office of Nuclear Physics through Grants No. DE-FG02-03ER41258, No. DE-AC05-00OR22725, No. DE-SC0008107 and No. DE-SC0014622, the U.S. National Science Foundation Grant No. PHY-0855584, the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canadian Foundation for Innovation (CFI), the Mexico National Council of Science and Technology (CONACYT) Grant No. 80444, and the UNAM research Grants (PAPIIT) No. IN111913 and No. IN109120. This research used resources of the Spallation Neutron Source of Oak Ridge National Laboratory, a DOE Office of Science User Facility. We also thank Michele Viviani (INFN Pisa) for very fruitful theory discussions and Jack Thomison (ORNL) for his engineering support.

Publisher Copyright:
© 2020 American Physical Society.

ASJC Scopus subject areas

  • Physics and Astronomy (all)


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