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

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

3. 3 Atmospheric Neutrinos (1) The most severe background to proton decay search 100MeV – 1000GeV  : e ~ 2 : 1 (low E ) p, He νeνe Super- K μ±μ± νμνμ π±π± atmosphere e±e± earth

4. 4 Interaction in the rock FC + PC through-going muons stopping muons Initial neutrino energy spectrum FC Through-going muons Stopping muons Event topology PC e + N  e + X  + N   + X  + N   + X

5. 5 First Hint (2.87kt·yr, 1988) dataMC events   e events   e single ring 17860 (0.34± 0.05) 232.5110.3 (0.47)  -like 8552144.0103.8 e-like93888.56.5

6. 6  /e Identification with a test beam

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

8. 8 Second Hint (7.7kt·yr, 1994) sub-GeV dataMC events   e events   e single ring 482182584.3270.5  -like 234158356.8247.9 e-like24824227.622.6

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

10. 10 Evidence for Oscillation of Atmospheric Neutrinos (33.0kt·yr, 1998) sub-GeV dataMC (+-20%) single ring 23892622.6  -like 11581573.6 e-like12311049.1

11. 11 Upward-going muons

12. 12  2 =170.8/170 d.o.f. at (sin 2 2  23,  m 23 2 )=(1.00, 2.0x10 -3 eV 2 )  2 =445.2/172 d.o.f. (null oscillation) 1489 day FC+PC data + 1646 day upward going muon data

13. 13 Allowed region of the oscillation parameters Assuming      oscillation Best fit  2 min = 170.8/170 d.o.f at (sin 2 2  23   m 23 2 ) = (1.0, 2.0 x 10 -3 eV 2 ) 90% CL allowed region sin 2 2  23  > 0.9 1.3x10 -3 <  m 23 2 <3.0x10 -3 (eV 2 ) Assuming null oscillation  2 = 445.2/172 d.o.f (complete SK-I dataset) Soudan-2 MACRO Super-K 68% CL 90% CL 99% CL

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

15. 15 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 Resurrection

16. 16 Next steps Tau appearance     + N   - + X Oscillation pattern Dip in L/E distribution P(    ) = 1 - cos 4   sin 2 2   sin 2 (1.27  m 23 2 L/E ) - P(   e  ) P(    e  ) = sin 2 2   sin 2   sin 2 (1.27  m 13 2 L/E ) 70 yr Monte Carlo  m 2 =2.5×10 -3 eV 2

17. 17 K2K long baseline neutrino oscillation experiment 5.6×10 19 pot (June 1999 – July 2001) 250 km

18. 18 Best fit 1R  spectrum & Nsk Best fit point (sin 2 2  23,  m 23 2 ) = (1.0, 2.8x10 -3 eV 2 ) KS test prob.(shape): 79% N SK =54 (Obs.=56) Very good agreement in shape & N SK with atmospheric neutrinos Expected w/o oscillation Normalized w/o oscillation Normalized with best fit oscillation Total number of obs. Events: 5616 (Jan03-Apr03) Expected w/o oscillation: 80.6 +7.3-8.0 24 +2.3-2.1

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

20. 20 JHFMINOSK2K E(GeV)5012012 Int.(10 12 ppp)330406 Rate(Hz)0.290.530.45 Power(MW) Phase-II 0.77 4 0.410.0052 50 GeV JHF PS 2007 Kamioka

21. 21 Expected sensitivities (5yrs) 0.01 1×10 -4 True  m 23 2 (eV 2 )  (sin 2 2  ) ~ 0.01  (  m 2 ) ~ <1×10 -4 OAB-2degree  disappearance w/ beam MC, & full SK det. simulation  (sin 2 2   )  (  m 23 2 ) excluded by reactor ~0.5 sin 2 2  13 >0.006 (90%) sin 2 2  13 >0.018 (3  ) x20 Sensitivity in 5 years NBB 1.5GeV NBB 3 GeV e appearance

22. 22 Hyper-Kamiokande (1Mt water) 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 (50cm  )

23. 23 Thank you

24. 24 Oscillation Among 3 Flavors P(    e  ) = sin 2 2   sin 2   sin 2 (1.27  m 13 2 L/E ) P(    ) = 1 - cos 4   sin 2 2   sin 2 (1.27  m 23 2 L/E ) - P(   e  ) sin 2  13 < 0.1, cos 4  13  ~  1 (from the CHOOZ experiment) sin 2 2   ~ sin 2 2  23 ~ 1, sin 2 2   e = sin 2 2  13 sin 2  23 ~ 0.5 sin 2 2  13 ~ 2|U e3 | 2 m3m3 m2m1m2m1 m 3 >> m 2 > m 1