Magneto-$ν$: Heavy neutral lepton search using $^{241}$Pu $β^-$ decays
C. Lee, X. Zhang, A. Kavner, T. Parsons-Davis, D. Lee, N. Hines, S. T. P. Boyd, M. Loidl, X. Mougeot, M. Rodrigues, M. K. Lee, J. Song, R. Wood, I. Jovanovic, G. B. Kim
公開日: 2025/3/24
Abstract
We present experimental $^{241}$Pu $\beta$ decay spectra as part of the Magneto-$\nu$ experiment aimed at searching for keV heavy neutral leptons. A total of 194 million $\beta$ decays are measured by metallic magnetic calorimeters, representing the highest statistical precision achieved for $^{241}$Pu to date. The endpoint energy of $^{241}$Pu $\beta$ decay is measured with respect to $\gamma$ and $X$ rays from an external $^{133}$Ba source, yielding a value of 22.264\,(40)\,keV. The spectrum is statistically consistent to that of an allowed decays, and no strong sign of deviation was observed. Using a fraction of the high-statistics spectra, we set an upper limit on the admixture of a 11.5\,keV sterile neutrino to the electron neutrino at $|U_{e4}|^2 < 1.31 \times 10^{-3}$.