First Results from the Sudbury Neutrino Observatory

TL;DR

The Sudbury Neutrino Observatory's initial results provide evidence for neutrino flavor change and measure the active 8B solar neutrino flux, supporting neutrino oscillation theories independent of solar models.

Contribution

First experiment to detect all neutrino flavors from the Sun using a large D2O Cherenkov detector, enabling model-independent tests of neutrino oscillations.

Findings

Detected solar neutrinos via CC and ES interactions.

Observed a 3.3 sigma difference indicating active neutrino component.

Measured the active 8B neutrino flux consistent with solar models.

Abstract

The Sudbury Neutrino Observatory (SNO) is a water imaging Cherenkov detector. Utilising a 1 kilotonne ultra-pure D2O target, it is the first experiment to have equal sensitivity to all flavours of active neutrinos. This allows a solar-model independent test of the neutrino oscillation hypothesis to be made. Solar neutrinos from the decay of 8B have been detected at SNO by the charged-current (CC) interaction on the deuteron and by the elastic scattering (ES) of electrons. While the CC interaction is sensitive exclusively to electron neutrinos, the ES interaction has a small sensitivity to muon and tau neutrinos. In this paper, the recent solar neutrino results from the SNO experiment are presented. The measured ES interaction rate is found to be consistent with the high precision ES measurement from the Super-Kamiokande experiment. The electron neutrino flux deduced from the CC interaction rate in SNO differs from the Super-Kamiokande ES measurement by 3.3 sigma. This is evidence of an active neutrino component, in addition to electron neutrinos, in the solar neutrino flux. These results also allow the first experimental determination of the active 8B neutrino flux from the Sun, and this is found to be in good agreement with solar model predictions