The HUNTER (Heavy Unseen Neutrinos from Total Energy-momentum Reconstruction) collaboration brings together AMO, NP and HEP researchers to search for additional “sterile” neutrinos beyond the Standard Model of particle physics. HUNTER is an apparatus for radioactive atom trapping and high resolution decay-product spectrometry. It is built around a high occupancy, low temperature Magneto-Optical Trap (MOT), loaded from a source of radioactive 131 Cs through a subsidiary loading MOT. The MOT is viewed by large acceptance, high resolution electrostatic spectrometers (“Reaction Microscope”) to detect the recoil ions and Auger electrons from electron-capture (EC) decays in the trap, plus a position-sensitive scintillator array measuring vector momentum of atomic x-rays. HUNTER will allow event-by-event missing mass reconstruction of EC decays, seeking a separated nonzero mass peak from massive sterile neutrinos.This proposal leverages $1.2M in funding we have received from the W. M. Keck Foundation, plus substantial institutional contributions.

One of many essential technical developments for HUNTER is our "orthotropic oven" (T. Dinneen et al., Rev. Sci. Inst. 67, 752(1996)) which allows efficient MOT loading with the commercially available radioactive (0.1 Ci / µg) 131-Cs source material