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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 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 • 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
Motivation – Why Study 13? MINOS 2010 CHOOZ • Finding 13 = 0 may point to a new symmetry 2.3210-3 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
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
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
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
Improvements to the Analysis Since 2010 result: • 1.21020PoT (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
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
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
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
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
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
The Far Detector Energy Spectrum Search for Electron Neutrino Appearance in MINOS
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
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
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 sin2213 = 0.041 Search for Electron Neutrino Appearance in MINOS
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(213) < 0.12 (0.20) [90% C.L.] • sin2(213) = 0.041 (0.079) [Best Fit] • sin2(213) = 0 excluded at 89% C.L. Search for Electron Neutrino Appearance in MINOS
BACKUP SLIDES Search for Electron Neutrino Appearance in MINOS
Probability of e Appearance Search for Electron Neutrino Appearance in MINOS
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
Far Detector Events in Analysis Region Search for Electron Neutrino Appearance in MINOS
5-6 GeV Events Search for Electron Neutrino Appearance in MINOS
Best Fit Shown on Counting Experiment Energy Spectrum Search for Electron Neutrino Appearance in MINOS
Overlay of MINOS and T2K Allowed Regions NOT a combined fit * * arXiv:1106.2822 Search for Electron Neutrino Appearance in MINOS