Wavelet Approach to Search for Sterile Neutrinos in Tritium $\beta$-Decay Spectra

TL;DR

This paper introduces a wavelet transform method to detect tiny spectral distortions caused by sterile neutrinos in tritium beta decay, achieving high sensitivity and robustness against systematic effects.

Contribution

It demonstrates that wavelet analysis can effectively identify sterile neutrino signatures in beta decay spectra with high sensitivity and minimal systematic bias.

Findings

Sensitivity to active-sterile mixing angle down to 10^{-6}

Wavelet method is robust against smooth spectral systematics

Requires high-resolution spectral measurements (~100 eV FWHM)

Abstract

Sterile neutrinos in the mass range of a few keV are candidates for both cold and warm dark matter. An ad-mixture of a heavy neutrino mass eigenstate to the electron neutrino would result in a minuscule distortion - a 'kink' - in a $\beta$-decay spectrum. In this paper we show that a wavelet transform is a very powerful shape analysis method to detect this signature. For a tritium source strength, similar to what is expected from the KATRIN experiment, a statistical sensitivity to active-to-sterile neutrino mixing down to $\sin^2 \theta= 10^{-6}$ ($90\%$ CL) can be obtained after 3 years of measurement time. It is demonstrated that the wavelet approach is largely insensitive to systematic effects that result in smooth spectral modifications. To make full use of this analysis technique a high resolution measurement (FWHM of $\sim100$~eV) of the tritium $\beta$-decay spectrum is required.