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 -1≤cosθ[subscript zenith]≤0.4 in a total exposure of 2.30×10[superscript 14] cm[superscript 2] s. The measured flux normalization is 1.22±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 cosθ[subscript zenith]>0.4 is measured to be (3.31±0.01(stat)±0.09(sys))×10[superscript -10] μ/s/cm[superscript 2].