The Sudbury Neutrino Observatory: Solving the Solar Neutrino Problem
Art McDonald
SNO Institute, Queen's University, Kingston, Ontario, Canada
Colloquium, Argonne National Laboratory
October 25, 2002

The Sudbury Neutrino Observatory (SNO) is a 1,000 tonne heavy water Cerenkov-based neutrino detector situated 2,000 meters underground in INCO's Creighton Mine near Sudbury, Ontario, Canada. Previous measurements of solar neutrino fluxes are all smaller than predicted by solar model calculations, which has come to be known as the Solar Neutrino Problem. Either the solar model calculations are incomplete or some of the electron neutrinos produced in the sun are changing to another flavor enroute to earth. To resolve this problem SNO is able use the neutrinos from 8B decay in the Sun to observe one neutrino reaction sensitive only to solar electron neutrinos and others sensitive to all active neutrino types and thereby can search for direct evidence of neutrino flavor change. Results from the multi-year SNO observation program will be presented. Clear evidence for flavor change of solar neutrinos will be presented. The implications of this result for particle physics theory, solar physics and cosmology will be discussed. The future phases for SNO will provide enhanced sensitivity for further measurements of solar neutrino properties, atmospheric neutrinos and supernova neutrinos.