By extending our analysis and simulations of our 37K β-decay data set to allow the β asymmetry with respect to nuclear spin to vary with β energy Eβ, we have gained sensitivity to new physics that depends on a helicity factor for the β, mβ/Eβ. 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 ± 0.084 (stat) ± 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.
@article{arxiv.2509.11502,
title = {$A_{\beta}[E_{\beta}]$ in $^{37}$K decay: new physics with opposite $\beta$ helicity},
author = {Melissa Anholm and J. A. Behr and D. G. Melconian and G. Gwinner and A. Gorelov and J. C. McNeil and B. Fenker and S. Behling},
journal= {arXiv preprint arXiv:2509.11502},
year = {2026}
}
Comments
Observable now labelled b throughout, pedagogy including equations fixed. Included combined Abeta, b, fT constraint on revised exclusion plot more carefully