Manne Siegbahn Memorial Lecture

Neutrino and Astro-Physics Measurements with the Sudbury Neutrino Observatory

The Sudbury Neutrino Observatory (SNO) is a 1,000 tonne heavy-water-based neutrino detector in an ultra-clean environment created 2 km underground in a mine near Sudbury, Canada. Past measurements of solar neutrino fluxes have been smaller than predicted by solar model calculations, implying that the calculations are incomplete or that some of the electron neutrinos produced in the Sun change to another flavor en route to earth.

SNO has used 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 flavors and has found clear evidence for neutrino flavor change. This requires modification of the Standard Model for elementary particles and confirms solar model calculations with great accuracy.

Results from the multi-year SNO observation program will be presented, including details of the broad calibration program, extensive control and measurement of radioactive backgrounds and use of salt in the heavy water to enhance sensitivity to all active neutrino flavors.

The implications of the SNO results and other recent neutrino results for particle physics and solar physics will be discussed. The expansion of the underground facility to create a long-term international laboratory (SNOLAB) with a broad future experimental capability will also be described.