Neutrino Oscillations at Super-Kamiokande Soo-Bong Kim (Seoul National University)

Super- Kamiokande C Scientific American 42m 39m Water Cherenkov detector 1000 m underground 50,000 ton (22,500 ton fid.) 11, inch PMTs 1,885 anti-counter PMTs SK-I: Apr 1996 – Jul 2001 SK-II: Dec 2002 – Completed recovery from Nov 2001 accident ! PMT coverage: SK-I 40% SK-II 20% Full recovery attempt will start from the fall of 2005.

Super-Kamiokande is back to data-taking! (Dec. 10, 2002) SK-II cosmic ray muon sample Inner detector: ~5, inch PMT Outer detector: 1,885 8-inch PMT 20 inch PMT with Acrylic+FRP vessel SK-II

Contents  Results of atmospheric neutrino from SK-I:  Re-analysis based on updated MC (  interaction model/  flux/detector simulation), event reduction and event reconstruction  K2K results  Results of solar neutrinos from SK-I:  Detailed analysis on neutrino oscillations  Any time modulation on the observed flux

Neutrino Oscillation Two neutrino case  () = ( cos   sin  - sin  cos  ) 1 2 () P(  →  ) = sin 2 2  sin 2 (1.27  m 2 L/E)  m 2 = m m 1 2 (eV 2 ) L (km): Distance from source to detector E (GeV): Neutrino energy

Atmospheric Neutrinos  , K  e±e±  e   p, He... L=10-20 km ~10000 km Primary cosmic ray  / e ~ 2 ( < a few GeV) flux is up-down symmetric (> a few GeV)

Zenith Angle Distributions (old)   2-flavor oscillations ～ 15km ～ 13000km ～ 500km ～ 13000km ～ 500km Best fit (  m 2 =2.5x10 -3 eV 2, sin 2 2   2 min =163.2/170 d.o.f)  Null oscillation  (  2 =456.5/172 d.o.f)

Updates in atmospheric  analysis  New neutrino flux (Honda 2001)  Updated primary cosmic-proton flux  3D caculation  Improved hadron interaction model Cosmic proton flux

Updates in atmospheric  analysis  Improved neutrino interaction model: - changed M A  Tuned SK detector simulation: - light scattering parameters in water - PMT gain parameters of outer detector  Improved data reduction: - fully automated reduction scheme - lowered background of upward going  sample  Improved event reconstruction: - accurate ring search & automated reconstruction

Zenith Angle Distributions (new)   2-flavor oscillations Best fit (  m 2 =2.0x10 -3 eV 2, sin 2 2  )  Null oscillation (Honda)

   oscillations (  m 23 2 ) Best fit(  m 2 =2.0x10 -3,sin 2 2  =1.0  2 min =170.8/170 d.o.f)  m 23 2 = (1.3~3.0)x10 -3 eV 2 sin 2 2  23 > 0.9 (90%CL) (Assuming null oscillation:  2 =445.2/172 d.o.f) (Complete SK-I data set)

Allowed region for 3-flavor oscillations  m 2 =  m 23 2  m 13 2 ) getting close to CHOOZ’s limit on  13   e Atmospheric  m 23 2 =2x10 -3 eV 2 Solar  m 12 2 ~10 -5 eV 2 m1m1 m2m2 m3m3

K2K (KEK to Kamioka) Experiment

Super-K Event selection (K2K-I) T spill T SK GPS T Spill : Abs. time of spill start T SK : Abs. time of SK event TOF: 0.83ms (KEK to Kamioka) No Decay-e HE Trig. FC: fully contained (No activity in Outer Detector) FV: 22.5kt Fiducial Volume 1.5  s  500  sec  5  sec  T (  sec) FCFV 56 events !

Neutrino Interaction at Super-Kamiokande

Best Normalized by area fit point no oscillation GeV Reconstructed E shape at SK  29 1-R events in Nov 99- Jul 01) w/ oscillations (KS-test = 79%) Result of Neutrino Oscillations from K2K-I

(1.0, 2.8x10 -3 eV 2 ) K2K Best fit point = Null oscillation probability  < 1% Method1 0.7% Method2 0.4% Method1 2.8x10 -3 Method2 2.7x10 -3 Super-K result Two independent methods agree with each other K2K-I Results

Delivered Protons on Target (POT)  POT Protons/spill (2003/10/20) 8.3  POT K2K–I K2K–II SciBar detector installed

K2K Upgrade (SciBar Detector) Brand new near detector to study neutrino interactions below 1 GeV Scintillator + WLS fiber Scintillator: Fine segments (2×2×300cm 3 ) (made by Fermi-Lab, MINOS type) WLS fiber (1.5mmΦ x 360 cm) ~15,000 channels

Solar Neutrinos (5/31/1996 ~ 7/15/2001, 1496 days) =  Data SSM e e  e e scattering (contains 15% of NC) solar  events (14.5 events/day)

Solar Signal Shape Solar  Flux Time-Variatio n Background Shape Event Energy Event “Time” # Signal Events # Background Events in 21 bins 21 Energy bins Likelihood for solar neutrino extraction

+1.3 A DN =-1.8  1.6 % -1.2

Perihelion (Jan. 4th) Aphelion (July 5th) Time Variation of Observed Solar Neutrino Fluxes at Super-Kamiokande

Search for Periodic Modulation of Solar Neutrino Fluxes Lomb Periodogram Method