  EXO-200 is the first phase of the Enriched Xenon Observatory (EXO)
experiment, which searches for neutrinoless double beta decay in 136Xe to
measure the mass and probe the Majorana nature of the neutrino. EXO-200
consists of 200 kg of liquid Xe enriched to 80% in 136Xe in an ultra-low
background TPC. Energy resolution is enhanced through the simultaneous
collection of scintillation light using Large Area Avalanche Photodiodes
(LAAPD's) and ionization charge. It is being installed at the WIPP site in New
Mexico, which provides a 2000 meter water-equivalent overburden. EXO-200 will
begin taking data in 2009, with the expected two-year sensitivity to the
half-life for neutrinoless double beta decay of 6.4 10^25 years. According to
the most recent nuclear matrix element calculations, this corresponds to an
effective Majorana neutrino mass of 0.13 to 0.19 eV. It will also measure the
two neutrino mode for the first time in 136Xe.
