Searches for a sterile-neutrino admixture in detecting tritium decays in a proportional counter: New possibilities

Abstract

An experiment aimed at searches for an admixture of a sterile neutrino whosemass is 1 to 8 keV via detecting electrons from tritium decay in a proportional counter is proposed. The admixture in question can be discovered by a specific distortion of the energy spectrum of these electrons. For the above masses, the distortion extends over the whole spectrum; therefore, use can bemade of detectors that have a relatively low energy resolution (about 10 to 15%). A classic proportional counter is a simple and natural choice of detector for the decays of a gaseous tritium. The approach that we propose is novel in two respects. On one hand, the proportional counter used is made as a discrete unit in the form of a fully fused quartz tube. This permits a readout of current signals directly from the anode filament and ensures a high stability in the case of long-term measurements. At the same time, the application of state-of-the-art digital data-acquisition methods will make it possible to perform measurements under conditions of high counting rates—up to 10⁶ Hz. As a result, the energy spectrum of electrons from tritium decays that is formed by 10¹² counts could be accumulated within about a month. This data sample would make it possible to set an upper limit in the range of 10⁻³–10⁻⁵ on a sterile-neutrino admixture at a confidence level of three standard deviations (3σ) for m _s in the range of 1–8 keV, this being one to two orders of magnitude more stringent than present-day limits.