Stukel M, Hariasz L, Di Stefano P C F, Rasco B C, Rykaczewski K P, Brewer N T, Stracener D W, Liu Y, Gai Z, Rouleau C, Carter J, Kostensalo J, Suhonen J, Davis H, Lukosi E D, Goetz K C, Grzywacz R K, Mancuso M, Petricca F, Fijałkowska A, Wolińska-Cichocka M, Ninkovic J, Lechner P, Ickert R B, Morgan L E, Renne P R, Yavin I
Department of Physics, Engineering Physics & Astronomy, Queen's University, Kingston, Ontario K7L 3N6, Canada.
Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
Phys Rev Lett. 2023 Aug 4;131(5):052503. doi: 10.1103/PhysRevLett.131.052503.
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].
