Abstract:

A new generation of ambitious neutrinoless double beta decay experiments are coming online now, so we should expect that the neutrino mass frontier will be significantly pushed back in the next few years. EXO-200, the first such experiment to run, has been collecting physics data since May of this year. EXO-200 is based upon 200 kg of xenon enriched to 80% in Xenon-136, roughly one order of magnitude more source isotope than all previous experiments. With just the first month of data in hand, the experiment has already observed the ultra-rare two-neutrino double beta decay of Xenon-136, never before seen in this isotope (arXiv:1108.4193v1). The half-life of the two-neutrino decay, at $2.1 \times 10^{21}$ years, is the longest half-life ever directly observed in nature, despite the relatively modest amount of data which has been collected so far. EXO-200 is operating well and continuing to collect data, and first results from the search for the neutrinoless decay are expected soon.