Precision Measurement of the β Asymmetry in Spin-Polarized K 37 Decay

B. Fenker, A. Gorelov, D. Melconian, J. A. Behr, M. Anholm, D. Ashery, R. S. Behling, I. Cohen, I. Craiciu, G. Gwinner, J. McNeil, M. Mehlman, K. Olchanski, P. D. Shidling, S. Smale, C. L. Warner

Research output: Contribution to journalArticlepeer-review


Using Triumf's neutral atom trap, Trinat, for nuclear β decay, we have measured the β asymmetry with respect to the initial nuclear spin in K37 to be Aβ=-0.5707(13)syst(13)stat(5)pol, a 0.3% measurement. This is the best relative accuracy of any β-asymmetry measurement in a nucleus or the neutron, and is in agreement with the standard model prediction -0.5706(7). We compare constraints on physics beyond the standard model with other β-decay measurements, and improve the value of Vud measured in this mirror nucleus by a factor of 4.

Original languageEnglish
Article number062502
JournalPhysical Review Letters
Issue number6
StatePublished - 8 Feb 2018


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