EXO-200 Experiment
The Enriched Xenon Observatory (EXO) collaboration, centered at Stanford and SLAC, constructed and operated an apparatus to search for neutrinoless double beta decay. The "EXO-200" detector consists of what is called a Time Projection Chamber (TPC), filled with over 100 kilograms of liquid xenon enriched in the 136 isotope. The TPC was used to precisely determine the total energy and the spatial location of particle decays, and to thereby distinguish an interesting process from the background “noise” that results from natural radioactivity and cosmic rays. The experiment was constructed of ultra-low radioactivity materials and starting in 2011, operated about half a mile underground in order to attenuate cosmic rays in the DOE-operated WIPP facility near Carlsbad, New Mexico.
The collaboration published the most precise measurement of the half-life for the two-neutrino double beta decay process of about 2 x 1021 years, and a limit at greater than 1025 years for the neutrinoless double beta decay process – a limit that constrains the neutrino's mass to less than nearly one millionth of the electron's mass.
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