Direct evidence for neutrino flavor transformation from neutral-current interactions in SNO

The Sudbury Neutrino Observatory(SNO) is a 1,000 tonne heavy waterCerenkov‐based neutrino detectorsituated 2,000 meters underground in INCO’s Creighton Mine near Sudbury, Ontario, Canada. For the neutrinosfrom 8B decay in the Sun SNO observes the Charged Current neutrinoreaction sensitive only to electron neutrinosand others ( Neutral Currentand Elastic Scattering) sensitive to all active neutrinotypes and thereby can search for direct evidence of neutrinoflavor change. Using these reactions and assuming the standard 8B shape, the ve component of the 8B solar flux is φe = 1.76−0.05+0.05( stat.)−0.09+0.09 (syst.) × 106 cm−2s−1 for a kinetic energy threshold of 5 MeV. The non‐ve component is φμτ = 3.41−0.45+0.45( stat.)−0.45+0.48 (syst.) × 106 cm−2s−1, 5.3σ greater than zero, providing strong evidence for solar ve flavor transformation. The total flux measured with the NC reaction is φNC = 5.09−0.43+0.44( stat.)−0.43+0.46 (syst.) × 106 cm−2s−1, consistent with solar models. For charged currentevents, ...