Precision Measurement of the β Asymmetry in Spin-Polarized ^{37}K 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

doi:10.1103/PhysRevLett.120.062502

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

Phys Rev Lett. 2018 Feb 9;120(6):062502. doi: 10.1103/PhysRevLett.120.062502.

Authors

B Fenker^{1

2}, A Gorelov³, D Melconian^{1

2}, J A Behr³, M Anholm^{3

4}, D Ashery⁵, R S Behling^{1

6}, I Cohen⁵, I Craiciu³, G Gwinner⁴, J McNeil^{3

7}, M Mehlman^{1

2}, K Olchanski³, P D Shidling¹, S Smale³, C L Warner³

Affiliations

¹ Cyclotron Institute, Texas A&M University, 3366 TAMU, College Station, Texas 77843-3366, USA.
² Department of Physics and Astronomy, Texas A&M University, 4242 TAMU, College Station, Texas 77843-4242, USA.
³ TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia V6T 2A3, Canada.
⁴ Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada.
⁵ School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel.
⁶ Department of Chemistry, Texas A&M University, 3012 TAMU, College Station, Texas 77843-3012, USA.
⁷ Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada.

PMID: 29481259
DOI: 10.1103/PhysRevLett.120.062502

Abstract

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 ^{37}K to be A_{β}=-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 V_{ud} measured in this mirror nucleus by a factor of 4.