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 $-1\le \cos {\theta }_{\mathrm{zenith}}\le 0.4$ in a total exposure of $2.30\times {10}^{14}{\mathrm{cm}}^2\mathrm{s}$. The measured flux normalization is $1.22\pm 0.09$ 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 $\cos {\theta }_{\mathrm{zenith}}>0.4$ is measured to be $(3.31\pm 0.01(\mathrm{stat})\pm 0.09(\mathrm{sys}))\times {10}^{-10}\mu /\mathrm{s}/{\mathrm{cm}}^2$.

• Received 16 February 2009

DOI:https://doi.org/10.1103/PhysRevD.80.012001