N eutrino O scillation W orkshop Conca Specchiulla, September 11 th 2006 Michael Smy UC Irvine Low Energy Challenges in SK-III 50kt Water Cherenkov Detector with 11,146 20 PMTs located in Kamioka mine at N latitude and longitude ~2,400 m.w.e underground Super-Kamiokande April 1996-July 2001: (SK-I) Accident in November 2001 during maintenance Jan Oct. 2005: SK-II (half PMT density) July 2006 (SK-III) many physics topics; solar, atmospheric & accelerator s, proton decay Courtesy Y. Oyama 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! Conca Specchiula, 11 th September 2006 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 Solar Neutrino Problem Michael Smy, UC Irvine Solar Neutrino Problem Explained by SNO and Super-K as Neutrino Flavor Conversion! Michael Smy, UC Irvine Solar 95% 99.73% KamLAND Solar+KamLAND Michael Smy, UC Irvine Solar Neutrino Oscillation Parameters 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 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 SK-I: Angular distributions Rn, MeV MeV MeV 14-20MeV spallation e search Courtesy Y. Takeuchi SK-I Backgrounds Courtesy M. Nakahata 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 Vertex Reconstruction Michael Smy, UC Irvine 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 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 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 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: MeV dd d wall Event Selection (Tested at SK-II) Michael Smy, UC Irvine 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 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 Solar Peak at SK-II at 7MeV Michael Smy, UC Irvine Livetime 622 Days Livetime 622 Days 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 =-1.81.61.2% A DN =-6.34.3%(stat) SK-I SK-II SK-I+SK-II Michael Smy, UC Irvine Background Studies Michael Smy, UC Irvine Lantern Mantle Source contains large amounds of 208 Tl produces 60kBq of 2.6MeV s Michael Smy, UC Irvine 300 Lantern Mantles Lantern Mantle Source in SK-II x= cm y=-70.7 cm z= cm >6 MeV Michael Smy, UC Irvine 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 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