Proposed experiments to detect keV-range sterile neutrinos using energy-momentum reconstruction of beta decay or K-capture events

Abstract

Abstract Sterile neutrinos in the keV mass range may constitute the galactic dark matter. Various proposed direct detection and laboratory searches are summarized. It is suggested that a promising method for searching for keV sterile neutrinos in the laboratory is complete energy-momentum reconstruction of individual beta-decay or K-capture events, by measuring the vector momentum of all decay products from atoms suspended in a magneto-optical trap. Reconstruction of the ‘missing mass’ would isolate any keV-range sterile neutrinos as a separated population. A survey of suitable nuclides is presented, together with the measurement precision required in a typical experimental configuration. Among the most promising are the K-capture nuclides 131Cs, which requires measurement of an x-ray and several Auger electrons in addition to the atomic recoil, and 7Be which has only a single decay product but needs development work to achieve a trapped source. A number of background effects are discussed. It is concluded that, with current time-of-flight precision, sterile neutrinos with masses down to the 10 keV region would be detectable with relative couplings 10−5–10−6 in a 1–2 year running time, and with foreseeable future upgrades eventually able to reach coupling levels down to 10−10–10−11 using high-population trapped sources.