The HUNTER Sterile Neutrino Search Experiment: 131-Cs Magneto-Optical Trap Development*

The HUNTER experiment (Heavy Unseen Neutrinos from Total Energy-Momentum Reconstruction) is a search for sterile neutrinos with masses in the keV range. The neutrino missing mass will be reconstructed from 131-Cs electron capture decays occurring in a magneto-optically trapped (MOT) sample. Reaction-microscope spectrometers will detect all charged decay products with high solid angle efficiency and LYSO scintillators read out by silicon photomultiplier arrays will detect x-rays, each with sufficient resolution to reconstruct the neutrino missing mass. The short half-life of about 9.5 d of 131-Cs paired with the requirement to run the experiment over timescales of order one year to obtain the target sensitivity present special challenges for the MOT. We will present progress on the 131-Cs MOT development and implementation at UCLA.