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DISCOVERY OF ATMOSPHERIC MUON NEUTRINO OSCILLATIONS

DISCOVERY OF ATMOSPHERIC MUON NEUTRINO OSCILLATIONS. Yoji Totsuka For Kamiokande and Super-Kamiokande Collaborators. Prologue First Hint in Kamiokande Second Hint in Kamiokande Evidence found in Super-Kamiokande Nov-12 Accident Progress in the K2K Experiment Future.

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DISCOVERY OF ATMOSPHERIC MUON NEUTRINO OSCILLATIONS

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  1. DISCOVERY OF ATMOSPHERIC MUON NEUTRINOOSCILLATIONS Yoji Totsuka For Kamiokande and Super-Kamiokande Collaborators • Prologue • First Hint in Kamiokande • Second Hint in Kamiokande • Evidence found in Super-Kamiokande • Nov-12 Accident • Progress in the K2K Experiment • Future

  2. Kamiokande Detector(KamiokaNucleon Decay Experiment) • Search for proton decay • 3000ton water • 1000 50cmf PMT (20% photo coverage) • 1000m underground • Min det. energy ~ 20 MeV(later ~ 7 MeV) • 1983-1996

  3. p, He atmosphere π± μ± Super-K e± νe νμ earth Atmospheric Neutrinos (1) • The most severe background to proton decay search • 100MeV – 1000GeV • nm : ne ~ 2 : 1(low En)

  4. Event topology ne + N  e + X nm + N  m + X nt + N t + X FC PC Initial neutrino energy spectrum Stopping muons Through-going muons FC + PC stopping muons Interaction in the rock through-going muons

  5. First Hint (2.87kt·yr, 1988)

  6. m/e Identification with a test beam

  7. q q Atmospheric Neutrinos (2) Up-down symmetry of the flux Earth

  8. Second Hint (7.7kt·yr, 1994)

  9. ４１．４ｍ ４０ｍ Super-Kamiokande (1996) • 1996- • 50000ton water • 11146 50cmf PMT (40% photo coverage) • 1000m underground • Min det. energy ~ 5 MeV

  10. Evidence for Oscillation of Atmospheric Neutrinos(33.0kt·yr, 1998)

  11. Upward-going muons

  12. 1489 day FC+PC data + 1646 day upward going muon data c2=170.8/170 d.o.f. at (sin22q23, Dm232)=(1.00, 2.0x10-3eV2) c2=445.2/172 d.o.f. (null oscillation)

  13. Allowed region of the oscillation parameters (complete SK-I dataset) • Assuming nm nt oscillation • Best fit • c2min = 170.8/170 d.o.f • at (sin22q23,Dm232) = (1.0, 2.0 x 10-3 eV2) • 90% CL allowed region • sin22q23> 0.9 • 1.3x10-3 < Dm232 <3.0x10-3(eV2) • Assuming null oscillation • c2 = 445.2/172 d.o.f Soudan-2 MACRO Super-K 68% CL 90% CL 99% CL

  14. Nov-12 Accident 6777 ID + 1100 OD PMTs destroyed

  15. Resurrection • Partial rebuilding • 5248 ID PMTs (47% of pre-accident density) • 1885 OD PMTs • Ready by end 2002 • Full rebuilding • Additional 5898 new ID PMTs • Ready by April 2007 As of April 1

  16. Next steps 70 yr Monte Carlo Dm2=2.5×10-3eV2 • Tau appearance • nm nt • nt + N  t- + X • Oscillation pattern • Dip in L/En distribution • P(nm  nm ) = 1 - cos4q13 sin22q23 sin2(1.27Dm232L/En)- P(nμ ne) • P(nμ ne) = sin22q13sin2q23sin2(1.27Dm132L/En)

  17. K2K long baseline neutrino oscillation experiment 5.6×1019pot (June 1999 – July 2001) 250 km

  18. Best fit 1Rm spectrum & Nsk Total number of obs. Events: 56 16 (Jan03-Apr03) Expected w/o oscillation: 80.6+7.3-8.024 +2.3-2.1 • Best fit point (sin22q23 , Dm232)=(1.0, 2.8x10-3eV2) • KS test prob.(shape): 79% • NSK=54 (Obs.=56) • Very good agreement in shape & NSK with atmospheric neutrinos Expected w/o oscillation Normalized w/o oscillation Normalized with best fit oscillation

  19. T2K (Tokai-to-Kamioka) J-PARC Hyper-Kamiokande

  20. 50 GeV JHF PS 2007 Kamioka

  21. Expected sensitivities (5yrs) d(sin22q23) excluded by reactor x20 d(Dm232 ) ~0.5 sin22q13>0.006 (90%) sin22q13>0.018 (3s) nm disappearance ne appearance NBB 1.5GeV NBB 3 GeV 0.01 OAB-2degree 1×10-4 TrueDm232(eV2) d(sin22q) ~ 0.01 d(Dm2) ~ <1×10-4 in 5 years Sensitivity w/ beam MC, & full SK det. simulation

  22. Precision neutrino oscillation study Proton decay search R&D (complete in 2 years) Cavity excavation and its stability New light detector: Hybrid Photo-Detector, HPD (50cmf) Hyper-Kamiokande (1Mt water)

  23. Thank you

  24. m3 m2 m1 P(nμ ne) = sin22q13sin2q23sin2(1.27Dm132L/En) P(nm  nm ) = 1 - cos4q13 sin22q23 sin2(1.27Dm232L/En) - P(nμ ne) sin2q13 < 0.1, cos4q13~1 (from the CHOOZ experiment) sin22qmt ~ sin22q23 ~1, sin22qme = sin22q13 sin2q23~0.5 sin22q13 ~ 2|Ue3|2 Oscillation Among 3 Flavors m3 >> m2 > m1

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