The HUNTER Sterile Neutrino Search Experiment*

The HUNTER experiment (Heavy Unseen Neutrinos from Total Energy-momentum Reconstruction) is a search for sterile neutrinos with masses in the 20-280 keV range. The neutrino missing mass will be reconstructed from 131-Cs electron capture decays occurring in a magneto-optically trapped sample of atoms. Reaction-microscope spectrometers will be used to detect all charged decay products with high solid angle efficiency and LYSO scintillators read out by silicon photomultiplier arrays detect x-rays, each with sufficient resolution to reconstruct the neutrino missing mass. The experiment requires EUHV pressure, very uniform ion extraction electric field and electron confinement magnetic field, large solid angle for x-ray detection, and precision in-situ alignment. Procurement of major components of HUNTER is well underway with some innovative solutions to these requirements.