First observations of separated atmospheric ν_μ and ν̅ _μ events in the MINOS detector

Creators: Adamson, P.; Barish, B.; Choudhary, B. C.; Hanson, J.; Howcroft, C.; Kim, H.; Michael, D. G.; Newman, H. B.; Ochoa-Ricoux, J. P.; Peck, C. W.; Smith, C.; Trevor, J.; Zheng, H.; MINOS Collaboration

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 ν_μ and ν̅ _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 R^(data)_(up/down/R^(MC)_(up/down) = 0:62^(+0.19)_(0:14)(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 ν_μ and ν̅ _μ interactions are separated. The ratio of ν̅ _μ to ν_μ events in the data is compared to the Monte Carlo expectation assuming neutrinos and antineutrinos oscillate in the same manner, giving R^(data)_(ν_μ/ν̅ _μ) / R^(MC)_(ν_μ/ν̅ _μ) = 0.96^(+0:38)_(0.27)(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 ν_μ and ν̅ _μ .

Additional Information

© 2006 American Physical Society. Received 15 December 2005; published 6 April 2006. This work was supported by the U.S. Department of Energy, the U.K. Particle Physics and Astronomy Research Council, the U.S. National Science Foundation, the State and University of Minnesota, the Office of Special Accounts for Research Grants of the University of Athens, Greece, and FAPESP (Fundacao de Amparo a Pesquisa do Estado de Sao Paulo) and CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico) in Brazil. We gratefully acknowledge the Minnesota Department of Natural Resources for their assistance and for allowing us access to the facilities of the Soudan Underground Mine State Park. We also thank the crew of the Soudan Underground Physics Laboratory for their tireless work in building and operating the MINOS far detector.

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