A Simple Search for Sterile Neutrino Dark Matter

Abstract

We have tested the feasibility of an experiment to search for keV sterile neutrino dark matter with superconducting radiation detectors. For this, we have implanted radioactive 7 Be nuclei into our detectors, which decay by electron capture with a half-life of 53 days. The electron neutrino produced in this decay escapes from the detector, and we can measure the recoil energy of the 7 Li daughter nucleus with high accuracy. The recoil spectrum consists of four peaks, two due to capture of a 1s electron (“K-capture”) and two due to capture of a 2s electron (“L-capture”) for decay into the 7 Li ground state and the 7 Li* excited state. If the electron neutrino contains some admixture of a keV sterile neutrino, the 7 Li recoil energy will be shifted and produce an additional peak in the spectrum whose energy depends on the sterile neutrino mass and whose amplitude depends on the neutrino admixture.