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Arthur B. McDonald led work at the Sudbury Neutrino Observatory, which distinguished a change of neutrino flavor from a low total solar neutrino flux. Reactions on deuterium provided different flavor sensitivities: the charged-current channel selected electron neutrinos, while the neutral-current channel measured all active neutrino flavors. Their comparison revealed a non-electron component while the total flux agreed with solar expectations. The detector thereby tested the solar neutrino problem without requiring all missing electron-flavor events to mean missing solar production.^[ref]

A physicist working in experimental particle astrophysics.^[ref]

Raymond Davis Jr. developed a chemical method for observing solar neutrinos. In the chlorine experiment, rare interactions converted chlorine-37 into radioactive argon-37; extraction and counting of the argon atoms made a very weak interaction observable. The unexpectedly low measured rate became a central part of the solar neutrino problem.^[ref]

A chemist.^[ref]

The solar neutrino problem was the historical deficit of detected electron neutrinos relative to predictions based on solar fusion and detector response. The key ambiguity was whether the Sun emitted fewer neutrinos than expected or whether neutrinos changed flavor before reaching the detector.

The Sudbury Neutrino Observatory compared charged-current reactions sensitive primarily to electron neutrinos with neutral-current reactions sensitive to all active flavors. The electron-flavor flux was suppressed while a substantial non-electron active component was present, supporting flavor transformation rather than simply lowering the total solar production. Comparing channels therefore tested particle behavior independently of relying on one detector's count deficit.^[ref]