Sudbury Neutrino Observatory

The Sudbury Neutrino Observatory was a Canadian underground detector that used heavy water to measure solar neutrinos through charged-current and neutral-current reactions.

Heavy water: Water in which ordinary hydrogen is replaced by deuterium, an isotope containing one proton and one neutron. Deuterium nuclei enabled SNO’s distinctive charged-current and neutral-current measurements.
Solar neutrino problem: The historical mismatch between predicted and detected electron neutrinos from the Sun. SNO’s total-flux measurement showed that earlier detectors had missed neutrinos that changed flavor.
Creighton Mine: A deep underground nickel mine near Sudbury, Ontario, Canada. SNO was built roughly two kilometres underground in this mine to shield it from cosmic rays.
SNO Phase I: The initial Sudbury Neutrino Observatory running period, using pure heavy water from 1999 to 2001. This phase established the charged-current solar-neutrino deficit.
Charged-current interaction: A weak interaction mediated by a W boson that changes a particle’s electric charge. SNO’s charged-current events detected solar electron neutrinos specifically.
Neutrino oscillation: The quantum-mechanical change of a neutrino’s flavor as it propagates. SNO’s results showed that solar electron neutrinos arrived on Earth as other active flavors too.
Arthur B. McDonald: A Canadian physicist who led the Sudbury Neutrino Observatory collaboration. McDonald directed the experiment whose solar-neutrino findings earned him the 2015 Nobel Prize.
SNO Phase II: The Sudbury Neutrino Observatory phase that added dissolved salt to enhance neutron detection. Salt improved neutral-current event detection and sharpened the total-flux measurement.
Neutral-current interaction: A weak interaction mediated by a Z boson that leaves the interacting particle’s electric charge unchanged. SNO’s neutral-current events measured the total flux of active solar-neutrino flavors.
Neutrino mass: The nonzero rest mass carried by each neutrino mass eigenstate. Flavor oscillations implied by SNO’s findings require neutrinos to have mass.

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