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Search for Electron Neutrino Appearance in MINOS

Search for Electron Neutrino Appearance in MINOS. Mhair Orchanian California Institute of Technology On behalf of the MINOS Collaboration DPF 2011 Meeting – Providence, RI August 8-13, 2011. Basics of Neutrino Oscillation. atmospheric. atmospheric.

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Search for Electron Neutrino Appearance in MINOS

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  1. Search for Electron Neutrino Appearance in MINOS Mhair Orchanian California Institute of Technology On behalf of the MINOS Collaboration DPF 2011 Meeting – Providence, RI August 8-13, 2011

  2. Basics of Neutrino Oscillation atmospheric atmospheric • 3 weak eigenstates 3 mass eigenstates • Related by the unitary leptonic mixing matrix U • Can compute the transition probability in the usual way: Search for Electron Neutrino Appearance in MINOS

  3. Motivation – Why Study 13? MINOS 2010 CHOOZ • Finding 13 = 0 may point to a new symmetry 2.3210-3 PhysRevD.82.051102 Phys.Lett.B466:415-430,1999 Sufficiently large 13 provides access to mass hierarchy and  through P(e) Finding CP-violation in the lepton sector may help explain baryon asymmetry in the universe Search for Electron Neutrino Appearance in MINOS

  4. How Do We Do It? • Need strong(er) event selection algorithm to improve 13 sensitivity MINOS designed and optimized to study disappearance Challenging to distinguish EM showers from hadronic showers Search for Electron Neutrino Appearance in MINOS

  5. How LEM Works • LEM (Library Event Matching) is based on pattern recognition algorithm • Uses raw hit information instead of reconstructed quantities 5 Bad match MC Search for Electron Neutrino Appearance in MINOS Original event MC • Good match MC

  6. The LEM PID Neural Net Reconstructed Energy Distributions for Signal and Background • Optimal cut: LEM > 0.7 • Optimal binning for PID shape fit: • 0.6 < LEM < 0.7 • 0.7 < LEM < 0.8 • 0.8 < LEM < 1.0 Search for Electron Neutrino Appearance in MINOS

  7. Improvements to the Analysis Since 2010 result: • 1.21020PoT (17%) more data • Improved event selection variable (LEM): 15% sensitivity gain • Shape fit: 12% sensitivity gain Counting expt with LEM 2010-style analysis with new data Shape fit with LEM CHOOZ upper limit Search for Electron Neutrino Appearance in MINOS

  8. Background Prediction Each background component (NC,  CC, beam e CC) “extrapolates” differently from Near Detector to Far Detector  must make prediction component-by-component For component  in analysis bin i: Search for Electron Neutrino Appearance in MINOS

  9. Background Prediction Different beam configurations Total data rate in each configuration MC component ratios between configurations  For component  (NC,  CC, beam e CC) in analysis bin i: Search for Electron Neutrino Appearance in MINOS

  10. Background Prediction Summing over energy bins: 60% NC 29%  CC 11% beam e CC Data components in standard configuration  For component  (NC,  CC, beam e CC) in analysis bin i: Search for Electron Neutrino Appearance in MINOS

  11. Background Prediction • Use ratio to extrapolate from Near to Far: • Flux (1/R2, acceptance, decay kinematics, focusing) • Fiducial volume • Energy smearing •  disappearance • Detector effects Note: Error bars are systematic. For component  (NC,  CC, beam e CC) in analysis bin i: Search for Electron Neutrino Appearance in MINOS

  12. Background Prediction Note: Predictions assume CP = 0, 23 = /4, normal mass hierarchy. Arise from  oscillations  base prediction on measured Near  CC spectrum For component  (NC,  CC, beam e CC) in analysis bin i: Search for Electron Neutrino Appearance in MINOS

  13. The Far Detector Energy Spectrum Search for Electron Neutrino Appearance in MINOS

  14. Outside the Signal Region Expect negligible signal for LEM < 0.5  use as test of entire analysis chain Predicted background (i.e., event count if 13 = 0): 370 19 (stat) Observed data: 377 Search for Electron Neutrino Appearance in MINOS

  15. The Far Detector LEM Distribution • Above optimal cut of 0.7: • Predicted background: 49.5 2.8 (syst)7.0 (stat) • Observed data: 62 (1.7 excess) Search for Electron Neutrino Appearance in MINOS

  16. Best Fit Official fit performed in 3 PID bins  5 reconstructed energy bins Assuming CP = 0, 23 = /4, and normal mass hierarchy, best fit is sin2213 = 0.041 Search for Electron Neutrino Appearance in MINOS

  17. Official Result arXiv:1108.0015 • Feldman-Cousins contours • Uncertainties in other oscillation parameters accounted for • Assuming CP = 0, 23 = /4, and normal (inverted) mass hierarchy: • sin2(213) < 0.12 (0.20) [90% C.L.] • sin2(213) = 0.041 (0.079) [Best Fit] • sin2(213) = 0 excluded at 89% C.L. Search for Electron Neutrino Appearance in MINOS

  18. BACKUP SLIDES Search for Electron Neutrino Appearance in MINOS

  19. Probability of e Appearance Search for Electron Neutrino Appearance in MINOS

  20. LEM Library • Library consists of 50 million Far Detector Monte Carlo Events • 20M eCC and 30M NC • Optimal library = large library with a fraction of 0.3 – 0.4 eCC • NC is sufficient to represent the background – CC events are either cut by preselection, or look very similar to NC hadronic showers. Fraction of library that is signal events Measure of sensitivity Total library size Search for Electron Neutrino Appearance in MINOS

  21. Far Detector Events in Analysis Region Search for Electron Neutrino Appearance in MINOS

  22. 5-6 GeV Events Search for Electron Neutrino Appearance in MINOS

  23. Best Fit Shown on Counting Experiment Energy Spectrum Search for Electron Neutrino Appearance in MINOS

  24. Overlay of MINOS and T2K Allowed Regions NOT a combined fit * * arXiv:1106.2822 Search for Electron Neutrino Appearance in MINOS

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