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N eutrino O scillation W orkshop Conca Specchiulla, September 11 th 2006 Michael Smy UC Irvine Low Energy Challenges in SK-III
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50kt Water Cherenkov Detector with 11,146 20” PMTs located in Kamioka mine at 36.43 0 N latitude and 137.31 0 longitude ~2,400 m.w.e underground Super-Kamiokande 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 ’s, proton decay Courtesy Y. Oyama
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Super-K Is Repaired! Michael Smy, UC Irvine began in fall 2005… …now finished! Village of Dou near Atotsu Mine Entrance Mozumi Mine Entrance …despite some weather problems!
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Conca Specchiula, 11 th September 2006
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Motivation for Lower Threshold 1.Extend Solar Neutrino Recoil Electron Spectrum to 4 MeV 2.Measure Gadolinium neutron captures with high efficiency (effective energy spectrum peaks at 5 MeV) 3.Measure reactor anti-neutrinos above 3 MeV Michael Smy, UC Irvine
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Solar Neutrino Problem Michael Smy, UC Irvine
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Solar Neutrino Problem Explained by SNO and Super-K as Neutrino Flavor Conversion! Michael Smy, UC Irvine
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Solar 95% 99.73% KamLAND Solar+KamLAND Michael Smy, UC Irvine Solar Neutrino Oscillation Parameters
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Solar Neutrino Future Measurements Still missing: oscillation signature! Lower energy real-time 8 B neutrino measurement in SK-III studies transition from vacuum oscillation to matter-dominated oscillations Michael Smy, UC Irvine
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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
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SK-I: Angular distributions Rn, 5.0-5.5MeV5.5-6.0MeV 8.0-8.5MeV 14-20MeV spallation e search Courtesy Y. Takeuchi
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SK-I Backgrounds Courtesy M. Nakahata
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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
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Vertex Reconstruction Michael Smy, UC Irvine
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New Vertex Fit: BONSAI Before: Clusfit, Kaifit, Hayai maximize (choose center of timing window for t 0 ) BONSAI: use likelihood; better maximization Michael Smy, UC Irvine
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BONSAI Performance in SK-II BONSAI 2.0 Clusfit Kaifit LINAC v=(-3.9,-0.7,12.0)m 5 MeV LINAC v=(-12.1,-0.7,-0.1)m 5 MeV LINAC v=(-12.1,-0.7,-12.1)m 5MeV Michael Smy, UC Irvine Energy (MeV) cm SK-II Monte Carlo
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BONSAI Performance in SK-I BONSAI 2.0 Clusfit Kaifit LINAC v=(-3.9,-0.7,12.0)m 5 MeV LINAC v=(-12.1,-0.7,-0.1)m 5 MeV LINAC v=(-12.1,-0.7,-12.1)m 5MeV Energy (MeV) cm SK-II Monte Carlo Michael Smy, UC Irvine Threshold Goal
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SK-I Reduction: BONSAI Fid. Cut Michael Smy, UC Irvine These Events already passed 2m d wall cuts from Hayai (online), Kai-Fit (online), Kai-Fit (offline) & Clusfit (offline) as well as an 8m d cut!! SK-I: 4.5-5 MeV dd d wall
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Event Selection (Tested at SK-II) Michael Smy, UC Irvine
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Reconstruction Quality Timing residual goodness: 0=bad, 1=good Direction goodness: azimuthal symmetry 0=good, 1=bad Reject non-Cherenkov events and misreconstructed events Michael Smy, UC Irvine Good Calibration Events Low Energy Sample
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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: g t 2 -g d 2 >0.25 Michael Smy, UC Irvine Good Calibration Events Low Energy Sample
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Solar Peak at SK-II at 7MeV Michael Smy, UC Irvine Livetime 622 Days Livetime 622 Days
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Recoil Electron Spectrum Michael Smy, UC Irvine 8 B MC only 8 B =2.33x10 6 /cm 2 s hep =15x10 3 /cm 2 s MC: A DN =-1.8±1.6±1.2% A DN =-6.3±4.3%(stat)
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SK-I SK-II SK-I+SK-II Michael Smy, UC Irvine
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Background Studies Michael Smy, UC Irvine
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Lantern Mantle Source contains large amounds of 208 Tl produces 60kBq of 2.6MeV ’s Michael Smy, UC Irvine 300 Lantern Mantles
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Lantern Mantle Source in SK-II x=-1661.45 cm y=-70.7 cm z=1559.8 cm >6 MeV Michael Smy, UC Irvine
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Lantern Mantle Source in SK-III Michael Smy, UC Irvine x=-71 cm y=71 cm z=1830 cm Clusfit BONSAI Clusfit BONSAI Clusfit BONSAIClusfit BONSAI
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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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