<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi>A</mi><mi>β</mi></msub><msub><mrow><mo>[</mo><mi>E</mi><mo>]</mo></mrow><mi>β</mi></msub></mrow></math> in <math xmlns="http://www.w3.org/1998/Math/MathML"><mmultiscripts><mi mathvariant="normal">K</mi><mprescripts></mprescripts><none></none><mn>37</mn></mmultiscripts></math> decay: New physics with opposite <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>β</mi></math> helicity

Melissa Anholm; J. A. Behr; D. G. Melconian; G. Gwinner; A. Gorelov; J. C. McNeil; B. Fenker; S. Behling

doi:10.1103/5khh-ltvw

Letter

$A_{β} {[E]}_{β}$ in ${}^{37}K$ decay: New physics with opposite $β$ helicity

Melissa Anholm^1,2, J. A. Behr ^1,2,3, D. G. Melconian^4,5, G. Gwinner ², A. Gorelov ¹, J. C. McNeil ^1,3, B. Fenker ^4,5, and S. Behling ^4,5,*

¹TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia V6T 2A3, Canada
²Department of Physics and Astronomy, University of Manitoba, Manitoba R3T 2N2, Canada
³Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, British Columbia V6T 1Z1, Canada
⁴Cyclotron Institute, Texas A&M University, 3366 TAMU, College Station, Texas 77843-3366, USA
⁵Department of Physics and Astronomy, Texas A&M University, 4242 TAMU, College Station, Texas 77843-4242, USA

^*Contact author: behr@triumf.ca

PDF

Phys. Rev. C 113, L012501 – Published 2 January, 2026

DOI: https://doi.org/10.1103/5khh-ltvw

Abstract

By extending our analysis and simulations of our ${}^{37}K β$ -decay data set to allow the $β$ asymmetry with respect to nuclear spin to vary with $β$ energy $E_{β}$ , we have gained sensitivity to new physics that depends on a helicity factor for the $β, m_{β} / E_{β}$ . In particular, we constrain Lorentz scalar and tensor quark-lepton interaction strengths at a sensitivity complementary to the similar Fierz interference term in neutron $β$ decay. Our result for that new physics is a Fierz interference term $b = 0.033 \pm$ 0.084 (stat) $\pm$ 0.039 (syst), consistent with the standard model electroweak interaction value $b = 0$ . We consider presently achieved complementarity to $β$ -decay and particle physics experiments, along with projectable technical improvements to our method.

Physical Review C

Export citation

Export citation

$A_{β} {[E]}_{β}$ in ${}^{37}K$ decay: New physics with opposite $β$ helicity

Abstract

Physics Subject Headings (PhySH)

Authorization Required

Other Options

References (Subscription Required)

Outline

Information

Filter

Filter

Article Lookup

Enter a citation

Aβ[E]β in K37 decay: New physics with opposite β helicity

Abstract

Physics Subject Headings (PhySH)

Authorization Required

Log in via your institution

Log in via APS Member Subscription

Other Options

References (Subscription Required)

$A_{β} {[E]}_{β}$ in ${}^{37}K$ decay: New physics with opposite $β$ helicity