First observations of separated atmospheric νμ and ν¯μ events in the MINOS detector

P. Adamson et al. (MINOS Collaboration)
Phys. Rev. D 73, 072002 – Published 6 April 2006

Abstract

The complete 5.4 kton MINOS far detector has been taking data since the beginning of August 2003 at a depth of 2070 meters water-equivalent in the Soudan mine, Minnesota. This paper presents the first MINOS observations of νμ and ν¯μ charged-current atmospheric neutrino interactions based on an exposure of 418 days. The ratio of upward- to downward-going events in the data is compared to the Monte Carlo expectation in the absence of neutrino oscillations, giving Rup/downdata/Rup/downMC=0.620.14+0.19(stat.)±0.02(sys.). An extended maximum likelihood analysis of the observed L/E distributions excludes the null hypothesis of no neutrino oscillations at the 98% confidence level. Using the curvature of the observed muons in the 1.3 T MINOS magnetic field νμ and ν¯μ interactions are separated. The ratio of ν¯μ to νμ events in the data is compared to the Monte Carlo expectation assuming neutrinos and antineutrinos oscillate in the same manner, giving Rν¯μ/νμdata/Rν¯μ/νμMC=0.960.27+0.38(stat.)±0.15(sys.), where the errors are the statistical and systematic uncertainties. Although the statistics are limited, this is the first direct observation of atmospheric neutrino interactions separately for νμ and ν¯μ.

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  • Received 15 December 2005

DOI:https://doi.org/10.1103/PhysRevD.73.072002

©2006 American Physical Society

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Vol. 73, Iss. 7 — 1 April 2006

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