EXO

EXO is a physics experiment to detect neutrinoless double beta decay of xenon-136 (¹³⁶Xe). The experiment is located underground in New Mexico, consisting of a tank of xenon with photodiodes: the xenon is both the substance decaying and the scintillator. Its design-concept was "10 tons of Xenon", aiming to detect instances of such decays despite a presumably very long half-life. The experiment began operation in 2011 with a reduced version (200 kg of xenon) called EXO-200, which produced double beta decays but none of them neutrinoless. In the process, it set some bounds on the timescales. An upcoming version, nEXO (for next-EXO), is to incorporate 5000 kg (5 metric tons) of xenon.