Measurement of the cosmic ray and neutrino-induced muon flux at the Sudbury neutrino observatory

Abstract

Results are reported on the measurement of the atmospheric neutrino-induced muon flux at a depth of 2 kilometers below the Earth's surface from 1229 days of operation of the Sudbury Neutrino Observatory (SNO). By measuring the flux of through-going muons as a function of zenith angle, the SNO experiment can distinguish between the oscillated and unoscillated portion of the neutrino flux. A total of 514 muonlike events are measured between $\ensuremath{-}1\ensuremath{\le}\mathrm{cos}{\ensuremath{\theta}}_{\mathrm{zenith}}\ensuremath{\le}0.4$ in a total exposure of $2.30\ifmmode\times\else\texttimes\fi{}{10}^{14}\text{ }\text{ }{\mathrm{cm}}^{2}\text{ }\mathrm{s}$. The measured flux normalization is $1.22\ifmmode\pm\else\textpm\fi{}0.09$ times the Bartol three-dimensional flux prediction. This is the first measurement of the neutrino-induced flux where neutrino oscillations are minimized. The zenith distribution is consistent with previously measured atmospheric neutrino oscillation parameters. The cosmic ray muon flux at SNO with zenith angle $\mathrm{cos}{\ensuremath{\theta}}_{\mathrm{zenith}}>0.4$ is measured to be $(3.31\ifmmode\pm\else\textpm\fi{}0.01(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.09(\mathrm{sys}))\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\text{ }\text{ }\ensuremath{\mu}/\mathrm{s}/{\mathrm{cm}}^{2}$.