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The neutrino physics groups at Unversity of Washington have been involved in many of the exciting results regarding neutrinos in the last 15 years. In 1998 the SuperK collaboration discovered neutrino oscillations, where neutrinos change flavor as they propagate. In 2001 the SNO collaboration discovered that neutrino oscillations were the reason for the apparent missing neutrinos from the Sun, and thus confirming models for the Sun's production of energy by solar fusion. The discovery that neutrinos oscillate means that neutrinos have mass, and studying the properties of these oscillations allows us to measure the difference between the square of the neutrino masses. The following are the big questions remaining about the nature of neutrinos:
- What is the absolute mass of the neutrinos? The mass of the neutrino played an important part in structure formation of the universe. By measureing the neutrino mass we could constrain models for the evolution of the universe.
- Are neutrinos their own antiparticle, i.e. Majorana in nature? There was a slight excess in the amount of matter over anti-matter in the early universe, and this excess allowed for a small amount of matter to survive creating the universe we see today. Leptogenesis is one of the best explainations for this slight excess of matter, and this requires neutrinos to be Majorana in nature.
- Do neutrinos violate CP? This is another requirement for leptogenesis.
Some of these big questions require us to answer other questions, like what is the neutrino mass hierarchy? Neutrino oscillation experiments can often tell us the absolute difference between the neutrino masses, but they cannot always tell us which is more massive. There are currently two prefered mass orderings.
Aside from measuring the nature of neutrinos, we also use neutrinos as probes to the energy production mechanism in astronomical objects, such as the Earth, Sun, and Supernova.