Direct Evidence for Neutrino Flavor Transformation from Neutral-Current Interactions in the Sudbury Neutrino Observatory

Abstract

Observations of neutral-current $\nu$ interactions on deuterium in the Sudbury Neutrino Observatory are reported. Using the neutral current (NC), elastic scattering, and charged current reactions and assuming the standard ${}^8\mathrm{B}$ shape, the ${\nu }_e$ component of the ${}^8\mathrm{B}$ solar flux is ${\phi }_e{=1.76\mathrm{}}_{-0.05\mathrm{}}^{+0.05\mathrm{}}\left(\mathrm{stat}{)}_{-0.09\mathrm{}}^{+0.09\mathrm{}}\right(\mathrm{syst})\times {10}^6{\mathrm{cm}}^{-2\mathrm{}}{\mathrm{s}}^{-1\mathrm{}}$ for a kinetic energy threshold of 5 MeV. The non- ${\nu }_e$ component is ${\phi }_{\mu \tau }{=3.41\mathrm{}}_{-0.45\mathrm{}}^{+0.45\mathrm{}}\left(\mathrm{stat}{)}_{-0.45\mathrm{}}^{+0.48\mathrm{}}\right(\mathrm{syst})\times {10}^6{\mathrm{cm}}^{-2\mathrm{}}{\mathrm{s}}^{-1\mathrm{}}$, $5.3\sigma$ greater than zero, providing strong evidence for solar ${\nu }_e$ flavor transformation. The total flux measured with the NC reaction is ${\phi }_{\mathrm{NC}}{=5.09\mathrm{}}_{-0.43\mathrm{}}^{+0.44\mathrm{}}\left(\mathrm{stat}{)}_{-0.43\mathrm{}}^{+0.46\mathrm{}}\right(\mathrm{syst})\times {10}^6{\mathrm{cm}}^{-2\mathrm{}}{\mathrm{s}}^{-1\mathrm{}}$, consistent with solar models.