A novel experimental system for the KDK measurement of the 40K decay scheme relevant for rare event searches

Stukel, Matthew; Rasco, B. C.; Brewer, N. T.; Stefano, P. C. F. Di; Rykaczewski, K. P.; Davis, Harold L.; Lukosi, Eric; Hariasz, L.; Constable, Marianne; Davis, Paul M.; Dering, K.; Fijałkowska, A.; Gai, Zheng; Goetz, K. C.; Grzywacz, R.; Kostensalo, Joel; Ninković, J.; Lechner, P.; Liu, Y.; Mancuso, M.; Melcher, Charles L.; Petricca, F.; Rouleau, Christopher M.; Squillari, P.; Stand, Luis; Stracener, D. W.; Suhonen, J.; Wolińska-Cichocka, M.; Yavin, Itay

doi:10.1016/j.nima.2021.165593

Cited by 4 publications

(9 citation statements)

References 35 publications

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“…The fully characterized KDK experimental setup [21] consists of a 40 K source, a sensitive x-ray silicon drift detector (SDD) and a near-100% efficient γ tagger (the Modular Total Absorption Spectrometer, MTAS [22]), as illustrated in Fig. 2.…”

Section: Detector and Analysismentioning

confidence: 99%

“…MTAS is a 1 tonne array of NaI scintillators with ≈98% tagging efficiency for the 1.46 MeV γ rays of interest (Table 7 in [21]). Data with the 40 K source were acquired over 44 days.…”

Section: Detector and Analysismentioning

confidence: 99%

“…Various factors will sort σ and σ * into coincident and anticoincident events; the main ones are (1) The efficiency with which the γ 's from EC * are tagged by MTAS is not perfect. We previously studied this parameter and determined it with high precision to be = 0.9792 ± 0.006 at a 2 µs coincidence window [21] using data and GEANT4 [25] simulations. This will reduce the expected number of EC * events that are properly tagged to σ * .…”

Section: B Coincident and Anticoincident Eventsmentioning

confidence: 99%

“…(3) In addition, some EC 0 events may be in spurious coincidence with the MTAS background; the probability that this occurs in the O(μs) coincidence window is β M t 1 [21] (false negatives). ( 4) The remaining EC 0 events are anticoincident.…”

Section: B Coincident and Anticoincident Eventsmentioning

confidence: 99%

“…An empirical frequency of this branch would also inform calculations in nuclear structure theory, including those for neutrinoless double-beta-decay half-lives. The KDK (potassium decay) Collaboration [20] has carried out the first measurement of EC 0 [14], using a novel detector configuration [21], as detailed in what follows.…”

Section: Introductionmentioning

confidence: 99%

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Evidence for ground-state electron capture of K40

Hariasz,

Stukel,

Di Stefano

et al. 2023

Phys. Rev. C

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Potassium-40 is a widespread, naturally occurring isotope whose radioactivity impacts estimated geological ages spanning billions of years, nuclear structure theory, and subatomic rare-event searches-including those for dark matter and neutrinoless double-beta decay. The decays of this long-lived isotope must be precisely known for its use as a geochronometer, and to account for its presence in low-background experiments. There are several known decay modes for potassium-40, but a predicted electron-capture decay directly to the ground state of argon-40 has never been observed. The existence of this decay mode impacts several fields, while theoretical predictions span an order of magnitude. Here we report on the first, successful observation of this rare decay mode, obtained by the KDK (potassium decay) Collaboration using a novel combination of a low-threshold x-ray detector surrounded by a tonne-scale, high-efficiency γ -ray tagger at Oak Ridge National Laboratory. A blinded analysis reveals a distinctly nonzero ratio of intensities of ground-state electron-captures (I EC 0 ) over excitedstate ones (I EC* ) of I EC 0 /I EC* = 0.0095 stat ± 0.0022 sys ± 0.0010 (68% CL), with the null hypothesis rejected at 4σ [Stukel et al., Phys. Rev. Lett. 131, 052503 (2023)]. In terms of branching ratio, this unambiguous signal yieldsroughly half of the commonly used prediction. This first observation of a third-forbidden unique electron capture improves our understanding of low-energy backgrounds in dark-matter searches and has implications for nuclear-structure calculations. For example, a shell-model based theoretical estimate for the neutrinoless double-beta decay half-life of calcium-48 is increased by a factor of 7 +3 −2 . Our nonzero measurement shifts geochronological ages by up to a percent; implications are illustrated for Earth and solar system chronologies.

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Section: Detector and Analysismentioning

confidence: 99%

“…MTAS is a 1 tonne array of NaI scintillators with ≈98% tagging efficiency for the 1.46 MeV γ rays of interest (Table 7 in [21]). Data with the 40 K source were acquired over 44 days.…”

Section: Detector and Analysismentioning

confidence: 99%