Rare ^{40}K Decay with Implications for Fundamental Physics and Geochronology

M Stukel; L Hariasz; P C F Di Stefano; B C Rasco; K P Rykaczewski; N T Brewer; D W Stracener; Y Liu; Z Gai; C Rouleau; J Carter; J Kostensalo; J Suhonen; H Davis; E D Lukosi; K C Goetz; R K Grzywacz; M Mancuso; F Petricca; A Fijałkowska; M Wolińska-Cichocka; J Ninkovic; P Lechner; R B Ickert; L E Morgan; P R Renne; I Yavin; KDK Collaboration

doi:10.1103/PhysRevLett.131.052503

Rare ^{40}K Decay with Implications for Fundamental Physics and Geochronology

Phys Rev Lett. 2023 Aug 4;131(5):052503. doi: 10.1103/PhysRevLett.131.052503.

Authors

M Stukel¹, L Hariasz¹, P C F Di Stefano¹, B C Rasco², K P Rykaczewski², N T Brewer^{2

3}, D W Stracener², Y Liu², Z Gai⁴, C Rouleau⁴, J Carter⁵, J Kostensalo⁶, J Suhonen⁷, H Davis^{8

9}, E D Lukosi^{8

9}, K C Goetz¹⁰, R K Grzywacz^{2

3

11}, M Mancuso¹², F Petricca¹², A Fijałkowska¹³, M Wolińska-Cichocka^{2

3

14}, J Ninkovic¹⁵, P Lechner¹⁵, R B Ickert¹⁶, L E Morgan¹⁷, P R Renne^{5

18}, I Yavin^{1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18}; KDK Collaboration

Affiliations

¹ Department of Physics, Engineering Physics & Astronomy, Queen's University, Kingston, Ontario K7L 3N6, Canada.
² Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
³ Joint Institute for Nuclear Physics and Application, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
⁴ Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
⁵ Berkeley Geochronology Center, Berkeley, California 94709, USA.
⁶ Natural Resources Institute Finland, Joensuu FI-80100, Finland.
⁷ Department of Physics, University of Jyväskylä, Jyväskylä FI-40014, Finland.
⁸ Department of Nuclear Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA.
⁹ Joint Institute for Advanced Materials, University of Tennessee, Knoxville, Tennessee 37996, USA.
¹⁰ Nuclear and Extreme Environments Measurement Group, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
¹¹ Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA.
¹² Max-Planck-Institut für Physik, Munich D-80805, Germany.
¹³ Faculty of Physics, University of Warsaw, Warsaw PL-02-093, Poland.
¹⁴ Heavy Ion Laboratory, University of Warsaw, Warsaw PL-02-093, Poland.
¹⁵ MPG Semiconductor Laboratory, Munich D-80805, Germany.
¹⁶ Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, Illinois 47907, USA.
¹⁷ U.S. Geological Survey, Geology, Geophysics, and Geochemistry Science Center, Denver, Colorado 80225, USA.
¹⁸ Department of Earth and Planetary Science, University of California, Berkeley, California 94720, USA.

PMID: 37595241
DOI: 10.1103/PhysRevLett.131.052503

Abstract

Potassium-40 is a widespread, naturally occurring isotope whose radioactivity impacts subatomic rare-event searches, nuclear structure theory, and estimated geological ages. A predicted electron-capture decay directly to the ground state of argon-40 has never been observed. The KDK (potassium decay) collaboration reports strong evidence of this rare decay mode. A blinded analysis reveals a nonzero ratio of intensities of ground-state electron-captures (I_{EC^{0}}) over excited-state ones (I_{EC^{*}}) of I_{EC^{0}}/I_{EC^{*}}=0.0095±[over stat]0.0022±[over sys]0.0010 (68% C.L.), with the null hypothesis rejected at 4σ. In terms of branching ratio, this signal yields I_{EC^{0}}=0.098%±[over stat]0.023%±[over sys]0.010%, roughly half of the commonly used prediction, with consequences for various fields [27L. Hariasz et al., companion paper, Phys. Rev. C 108, 014327 (2023)PRVCAN2469-998510.1103/PhysRevC.108.014327].