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 3 weak eigenstates  3 mass eigenstates – Related by the unitary leptonic mixing matrix U Can compute the transition probability in the usual way: atmospheric Mhair Orchanian (mho@caltech.edu)2Search for Electron Neutrino Appearance in MINOS

3. Motivation – Why Study  13 ? 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 Finding  13 = 0 may point to a new symmetry PhysRevD.82.051102 MINOS 2010 Mhair Orchanian (mho@caltech.edu)3Search for Electron Neutrino Appearance in MINOS Phys.Lett.B466:415-430,1999 2.32  10 -3 CHOOZ

4. How Do We Do It? MINOS designed and optimized to study  disappearance Challenging to distinguish EM showers from hadronic showers Need strong(er) event selection algorithm to improve  13 sensitivity EM Showers in MINOSDetector Parameters Radiation length: 1.76 cmSteel thickness: 2.54 cm Molière radius: 3.7 cmStrip width: 4.12 cm Mhair Orchanian (mho@caltech.edu)4Search 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 Mhair Orchanian (mho@caltech.edu)5Search for Electron Neutrino Appearance in MINOS Original event MC Good match MC Bad match MC

6. The LEM PID Mhair Orchanian (mho@caltech.edu)Search for Electron Neutrino Appearance in MINOS6 Reconstructed Energy Distributions for Signal and Background Neural Net 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

7. CHOOZ upper limit 2010-style analysis with new data Counting expt with LEM Shape fit with LEM Since 2010 result: ● 1.2  10 20 PoT (17%) more data ● Improved event selection variable (LEM): 15% sensitivity gain ● Shape fit: 12% sensitivity gain Improvements to the Analysis Mhair Orchanian (mho@caltech.edu)7Search 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: Mhair Orchanian (mho@caltech.edu)Search for Electron Neutrino Appearance in MINOS8

9. Background Prediction For component  (NC,  CC, beam e CC) in analysis bin i: Mhair Orchanian (mho@caltech.edu)Search for Electron Neutrino Appearance in MINOS9 Total data rate in each configuration  MC component ratios between configurations Different beam configurations

10. Background Prediction For component  (NC,  CC, beam e CC) in analysis bin i: Mhair Orchanian (mho@caltech.edu)Search for Electron Neutrino Appearance in MINOS10  Data components in standard configuration Summing over energy bins: 60% NC 29%  CC 11% beam e CC

11. Background Prediction For component  (NC,  CC, beam e CC) in analysis bin i: Mhair Orchanian (mho@caltech.edu)Search for Electron Neutrino Appearance in MINOS11 Use ratio to extrapolate from Near to Far: Flux (1/R 2, acceptance, decay kinematics, focusing) Fiducial volume Energy smearing  disappearance Detector effects Note: Error bars are systematic.

12. Background Prediction For component  (NC,  CC, beam e CC) in analysis bin i: Mhair Orchanian (mho@caltech.edu)Search for Electron Neutrino Appearance in MINOS12 Event Class sin 2 (2  13 ) 00.1 NC34.1  CC 6.7 e CC 6.46.2  CC 2.22.1 Total Background49.449.1   e CC 0.219.1 Note: Predictions assume  CP = 0,  23 =  /4, normal mass hierarchy. Arise from  oscillations  base prediction on measured Near  CC spectrum

13. The Far Detector Energy Spectrum Mhair Orchanian (mho@caltech.edu)13Search for Electron Neutrino Appearance in MINOS

14. Outside the Signal Region Mhair Orchanian (mho@caltech.edu)14Search for Electron Neutrino Appearance in MINOS 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

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

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 sin 2 2  13 = 0.041 Mhair Orchanian (mho@caltech.edu)16Search for Electron Neutrino Appearance in MINOS

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

18. BACKUP SLIDES Mhair Orchanian (mho@caltech.edu)18Search for Electron Neutrino Appearance in MINOS

19. Probability of e Appearance Mhair Orchanian (mho@caltech.edu)19Search for Electron Neutrino Appearance in MINOS

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

21. Far Detector Events in Analysis Region Mhair Orchanian (mho@caltech.edu)21Search for Electron Neutrino Appearance in MINOS

22. 5-6 GeV Events Mhair Orchanian (mho@caltech.edu)22Search for Electron Neutrino Appearance in MINOS

23. Best Fit Shown on Counting Experiment Energy Spectrum Mhair Orchanian (mho@caltech.edu)23Search for Electron Neutrino Appearance in MINOS

24. Overlay of MINOS and T2K Allowed Regions * arXiv:1106.2822 * NOT a combined fit Mhair Orchanian (mho@caltech.edu)24Search for Electron Neutrino Appearance in MINOS