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Low Energy Challenges in SK-III

N eutrino O scillation W orkshop. Low Energy Challenges in SK-III. Michael Smy UC Irvine. Conca Specchiulla, September 11 th 2006. 50kt Water Cherenkov Detector with 11,146 20” f PMTs located in Kamioka mine at 36.43 0 N latitude and 137.31 0 longitude ~ 2,400 m.w.e underground.

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Low Energy Challenges in SK-III

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  1. Neutrino Oscillation Workshop Low Energy Challenges in SK-III Michael Smy UC Irvine Conca Specchiulla, September 11th2006

  2. 50kt Water Cherenkov Detector with 11,146 20” f PMTs located in Kamioka mine at 36.430N latitude and 137.310 longitude ~2,400 m.w.e underground April 1996-July 2001: (SK-I) Accident in November 2001 during maintenance Jan. 2003-Oct. 2005: SK-II (half PMT density) July 2006 – (SK-III) many physics topics; solar, atmospheric & accelerator n’s, proton decay Super-Kamiokande Courtesy Y. Oyama

  3. …now finished! began in fall 2005… Super-K Is Repaired! …despite some weather problems! Mozumi Mine Entrance Village of Dou near Atotsu Mine Entrance Michael Smy, UC Irvine

  4. Conca Specchiula, 11th September 2006

  5. Motivation for Lower Threshold • Extend Solar Neutrino Recoil Electron Spectrum to 4 MeV • Measure Gadolinium neutron captures with high efficiency (effective energy spectrum peaks at 5 MeV) • Measure reactor anti-neutrinos above 3 MeV Michael Smy, UC Irvine

  6. Solar Neutrino Problem Michael Smy, UC Irvine

  7. Solar Neutrino Problem Explained by SNO and Super-K as Neutrino Flavor Conversion! Michael Smy, UC Irvine

  8. Solar Neutrino Oscillation Parameters Solar+KamLAND KamLAND 99.73% 95% Solar Michael Smy, UC Irvine

  9. Solar Neutrino Future Measurements • Still missing: oscillation signature! • Lower energy real-time 8B neutrino measurement in SK-III studies transition from vacuum oscillation to matter-dominated oscillations Michael Smy, UC Irvine

  10. How To Lower Threshold • Must reduce backgrounds… • Reduced Radon emission due to blast shields • Reduced Radon due to water flow change • Software Improvements: • Event Reconstruction • Event Selection • Background Studies Michael Smy, UC Irvine

  11. 5.0-5.5MeV 5.5-6.0MeV SK-I: Angular distributions Rn, g 8.0-8.5MeV ne search spallation 14-20MeV Courtesy Y. Takeuchi

  12. SK-I Backgrounds Courtesy M. Nakahata

  13. How To Lower Threshold • Must reduce backgrounds… • Reduced Radon emission due to blast shields • Reduced Radon due to water flow change • Software Improvements: • Event Reconstruction • Event Selection • Background Studies Michael Smy, UC Irvine

  14. Vertex Reconstruction Michael Smy, UC Irvine

  15. New Vertex Fit: BONSAI • Before: Clusfit, Kaifit, Hayai maximize (choose center of timing window for t0) • BONSAI: use likelihood; better maximization Michael Smy, UC Irvine

  16. LINAC v=(-3.9,-0.7,12.0)m 5 MeV BONSAI Performance in SK-II cm BONSAI 2.0 Clusfit SK-II Monte Carlo Kaifit LINAC v=(-12.1,-0.7,-0.1)m 5 MeV BONSAI 2.0 Clusfit Kaifit LINAC v=(-12.1,-0.7,-12.1)m 5MeV BONSAI 2.0 Clusfit Kaifit Energy (MeV) Michael Smy, UC Irvine

  17. Threshold Goal Threshold Goal LINAC v=(-3.9,-0.7,12.0)m 5 MeV BONSAI Performance in SK-I cm BONSAI 2.0 Clusfit SK-II Monte Carlo Kaifit LINAC v=(-12.1,-0.7,-0.1)m 5 MeV BONSAI 2.0 Clusfit Kaifit LINAC v=(-12.1,-0.7,-12.1)m 5MeV BONSAI 2.0 Clusfit Kaifit Energy (MeV) Michael Smy, UC Irvine

  18. dwall dg These Events already passed 2m dwall cuts from Hayai (online), Kai-Fit (online), Kai-Fit (offline) & Clusfit (offline) as well as an 8m dg cut!! SK-I Reduction: BONSAI Fid. Cut SK-I: 4.5-5 MeV Michael Smy, UC Irvine

  19. Event Selection(Tested at SK-II) Michael Smy, UC Irvine

  20. Good Calibration Events Reconstruction Quality • Timing residual goodness: 0=bad, 1=good • Direction goodness: azimuthal symmetry 0=good, 1=bad • Reject non-Cherenkov events and misreconstructed events Low Energy Sample Michael Smy, UC Irvine

  21. Good Calibration Events Reconstruction Quality • Timing residual goodness: 0=bad, 1=good • Direction goodness: azimuthal symmetry 0=good, 1=bad • Reject non-Cherenkov events and misreconstructed events • Hyperbolical cut: gt2-gd2>0.25 Low Energy Sample Michael Smy, UC Irvine

  22. Solar Peak at SK-II at 7MeV Livetime 622 Days Livetime 622 Days Michael Smy, UC Irvine

  23. MC: Recoil Electron Spectrum f8B=2.33x106/cm2s fhep=15x103/cm2s ADN=-1.8±1.6±1.2% ADN=-6.3±4.3%(stat) 8B n MC only 8B n MC only Michael Smy, UC Irvine

  24. SK-II SK-I+SK-II SK-I Michael Smy, UC Irvine

  25. Background Studies Michael Smy, UC Irvine

  26. Lantern Mantle Source • contains large amounds of 208Tl • produces 60kBq of 2.6MeV g’s 300 Lantern Mantles Michael Smy, UC Irvine

  27. Lantern Mantle Source in SK-II x=-1661.45 cm y=-70.7 cm z=1559.8 cm >6 MeV Michael Smy, UC Irvine

  28. Lantern Mantle Source in SK-III BONSAI BONSAI x=-71 cm y=71 cm z=1830 cm Clusfit Clusfit BONSAI BONSAI Clusfit Clusfit Michael Smy, UC Irvine

  29. Conclusions • energy threshold of 4 MeV for solar neutrinos is very ambitions for a large water Cherenkov detector… • …but we learned a lot from SK-II how to live with small # of photo-electrons! • we have better vertex reconstruction • we have a better event selection • we have a better understanding of the backgrounds Michael Smy, UC Irvine

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