The neutrino is the least understood of all the fundamental particles of the standard model. We know from neutrino oscillation experiments that there small differences between the neutrino masses, but we do not know the overall mass scale. Because the neutrino is chargeless it is possible that the neutrino is its own anti-particle, a so-called majorana neutrino. The SNO+ experiment aims to answer these questions by the search for the neutrinoless double beta decay, which is only possible if neutrinos are majorana particles. The rate of the decay process depends upon the neutrino mass scale. An observation and measurement of this effect would tell us key details about the fundamental nature of the neutrino and help us to understand this mysterious particle.
The SNO+ experiment makes use of the old SNO detector, which solved the solar neutrino problem, replacing the heavy water from SNO with liquid scintillator. The detector consists of 780 tons of liquid scintillator contained in a 6 m acrylic vessel observed by approximately 10000 photo-multiplier tubes mounted on an 18 m diameter geodesic support sphere. To shield the scintillator from external radioactivity the acrylic vessel is submerged in 7 kilotons of water. To protect the experiment from cosmic rays and to provide the best low radioactivity lab environment on Earth the detector is situated 2 km underground in the Creighton mine near Sudbury, Ontario, Canada. To search for neutrinoless double beta decay the liquid scintillator will be loaded with 0.5% by mass of Tellurium. Tellurium is an ideal candidate for a search for neutrinoless double beta decay due to a high isotopic abundance of the double beta decay isotope and an observable decay energy that is ideal for SNO+. The initial water run completed in summer 2017, the transition to liquid scintillator is ongoing and the measurement with Tellurium is expected to start in 2018.
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