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Stuart Mufson, Indiana University for the MINOS Collaboration ICRC Merida, Mexico July 7, 2007

Measurement of the Charge-Separated Atmospheric Neutrino-Induced Muons in the MINOS Far Detector. Stuart Mufson, Indiana University for the MINOS Collaboration ICRC Merida, Mexico July 7, 2007. Introduction. MINOS far detector: 5.4kT steel-scintillator sampling calorimeter

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Stuart Mufson, Indiana University for the MINOS Collaboration ICRC Merida, Mexico July 7, 2007

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  1. Measurement of the Charge-Separated Atmospheric Neutrino-Induced Muons in the MINOS Far Detector Stuart Mufson, Indiana University for the MINOS Collaboration ICRC Merida, Mexico July 7, 2007

  2. Introduction • MINOS far detector: • 5.4kT steel-scintillator sampling calorimeter • located at Soudan Underground Laboratory, MN, 710m below surface • deepest underground magnetized detector that can distinguish -induced + from - • can distinguish upward-going -induced muons from downward cosmic muons with excellent timing resolution -- 2.31+/- 0.03 ns • further details in hep-ex/0701045 coordinate system for analysis

  3. -Induced Up-Going Muons • -induced muons: events from below or slightly above the horizon • sample uncontaminated by cosmics • upward events separated from downward events by fitting a straight line to the trajectory • 1/ ≈ 1  upward-going; 1/ < 0  downward-going • typical upward-going muon • 1/ = T/ S ≈ 1 • T = time from 1st hit • S = distance from 1st hit

  4. -Induced Up-Going Muons • 1/ distribution: -induced upward-going muons cosmic muons   1% of peak cut at 1% of peak

  5. Oscillation Analysis • oscillation signal in MINOS most evident at low measured momenta • distributions of muons in far detector without oscillations and with SuperK values of oscillation parameters

  6. Oscillation Analysis • evidence for oscillations: deviation of the ratio of low momentum to high momentum -induced muons from expectation • data separated into 3 data sets -- “low” energy (L), “high” energy (H), “unknown” energy (U) • parent energy of neutrinos yielding muons in L, H, and U data sets

  7. Oscillation Analysis • Results: • “Data” = MINOS far -induced muons • “Bkd” = background • “MC” = Monte Carlo expectation without oscillation • High/Low ratio in data compared with Monte Carlo expectation in the absence of oscillations • in the absence of oscillation, ratio ≈ 1 • ratio differs from unity by 2.0

  8. Oscillation Analysis • Further evidence for an oscillation signal is seen in the distribution of the combined low momentum and high momentum data samples when compared with MC expectation for no oscillation • clear deficit of events at low momenta

  9. Oscillation Analysis • momentum-separated muons (L, H, U) separated into 3 cos() bins • oscillation parameters found by comparing data and MC with the 2 statistic • where the ’s are the systematic errors

  10. Oscillation Analysis • a grid search gives the best-fit oscillation parameters in the phyiscal region best-fit in physical region MINOS beam parameters MC no oscillation

  11. Oscillation Analysis • confidence intervals for the MINOS oscillation fit 68% confidence interval 90% confidence interval 90% confidence interval for MINOS contained vertex analysis for 418 days of data taking MINOS best fit

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