Searching for double beta decay with the Enriched Xenon Observatory

Abstract

The Enriched Xenon Observatory (EXO) will search for neutrinoless double beta decay in 136Xe. The first phase of the experiment, EXO-200, uses 200 kg of liquid xenon enriched to 80% in 136Xe in an ultra-low background time projection chamber (TPC). EXO-200 is in the final stages of assembly at the WIPP site in Carlsbad, NM and will begin taking data in 2009 with two-year sensitivity to the half-life for neutrinoless double beta decay of 6.4 × 1025 years. According to nuclear matrix element calculations, this corresponds to an effective Majorana neutrino mass of 0.13 to 0.19 eV. The EXO collaboration is also performing R&D for simultaneous detection of the decay electrons and emerging Ba ion allowing essentially background free detection in a future, ton-scale detector. The status of EXO-200 and of the ion tagging technology in liquid xenon is described.