1. Present and Future of Super-Kamiokande Experiment Chen Shaomin Center for High Energy Physics Tsinghua University

2. Super-Kamiokande detector 41.4 m 39.3 m A 50k tons water Č detector located at 1k m underground

3. Physics topics in Super-Kamiokande  Nucleon decay  Solar neutrino  Atmospheric neutrino  Neutrinos from supernova burst  Long baseline neutrino oscillation  Massive neutrino dark matter search  Gamma-ray burst search …

4. Super-Kamiokande collaboration Initially (1992): Japan, USA Later: Korea, Poland Now: China ~ 140 Scientists and ~ 35 Institutions

5. History of Super-Kamiokande 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 Start SK-I Accident Partial reconstruction SK-II Full reconstruction SK-III 11,146 (40%) 5,182 (19%) 11,129 (40%) # of PMTs Threshold 5 MeV 7 MeV 4 MeV(plan) Achievement Discovery of atmosphere oscillation Discovery of Solar oscillation Discovery of Atmosphere L/E effect K2K final result

6. From SK-II to SK-III SK-I in 2006 accidence PMT with FRP mask Partial reconstruction Full reconstruction SK-III in 2006 SK-II in 2002 5,182 PMTs 11,129 PMTs

7. Detector goals in SK-III  Lower energy threshold  Extend energy range Special trigger logic? Change electronic threshold? Lower water temperature from 13°C to 10°C? Adding Gd in water? … Improved from 0 – 300 p.e.s/PMT to 0 – 1250 p.e.s./PMT with newly designed electronics. Down to 4 MeV Up to multi TeV scale

8. Neutrino detection in SK If  + /  – is fully contained in the inner tank If e + /e – is fully contained in the inner tank Ring pattern diff. used for PID Cone vertex and # of PMT and total charge collected used for measuring Evis

9. Far detector for K2K/T2K K2K L=250km E ~1GeV L Far detector Near detector KEK-TO-KAMIOKANDE TOKAI-TO-KAMIOKANDE KEK Tokai T2K L=295km E ~0.75GeV To Beijing?

10. Beam @Super-K ND SK Time-of-Flight < 1 msec  Fully contained  Evis  20 MeV  Fiducial volume (<2m)  Timing requirement: -0.2<Tsk-Tspill-T.O.F<1.3  sec TspillTsk GPS To detect beam @SK K2K

11. Solar/Supernova neutrinos  SUN Neutrino scatters electron in detector We observe the electron and can know the origin Neutrino from the Sun/Supernova (low energy neutrinos)

12. Supernova neutrino burst SN1987A BeforeAfter

13. Key issues in Supernova study “BANG” When and where? Precise measurement on 1 st bounce of e ’s can be a key step to determine absolute neutrino mass. Time spectrum of supernova neutrinos

14. Supernova event rate at SK 5MeV threshold ~7,300 e +p events ~300 +e events ~100 e + 16 O events for 10 k pc supernova (- ) T.Totani, K.Sato, H.E.Dalhed and J.R.Wilson, ApJ.496,216 (1998) Lower the energy threshold can get more sensitivity

15. Direction to Supernova Direction of supernova can be determined with an accuracy of 2-3 degrees. +e e +p Separation between +e  + e and e + p  n + e + can improve the accuracy

16. Neutrinos from all past core-collapse supernovas Population synthesis (Totani et al., 1996) Constant SN rate (Totani et al., 1996) Cosmic gas infall (Malaney, 1997) Cosmic chemical evolution (Hartmann et al., 1997) Heavy metal abundance (Kaplinghat et al., 2000) LMA oscillation (Ando et al., 2002) Electron-type antineutrino energy (MeV) Golden region is the easiest to detect @SK

17. What do we learn from SK-I? Total background Atmospheric  → invisible  → decay e Atmospheric e 90% CL limit of SRN

18. SK SRN limit vs. predictions SK-I upper limit: < 1.2 /cm 2 /sec We hope to improve the limit by tagging neutron in process

19. Muon background Invisible   Decay e Possible  -ray emission  T = ~ 2  sec 16 O Pre-activity Post-activity     e    e possible  + production

20. Possibilities of tagging neutron e e+e+ p n   Positron and gamma ray vertices are within ~50cm. p Gd 2.2 MeV   t ~ 200  s 8 MeV   t ~ 30  s e could be identified by tagging the delay neutron.

21. Trigger logic to tag neutrons Average # of PMT hits ~ 7 @ SK, lower than the trigger threshold and the requirement for a good gamma vertex reconstruction # of PMT hits 2.2MeV 

22. PMT timings for 2.2MeV  ’s # of PMT hits PMT timings (ns) # of PMT hits PMT timings (ns) Time of flight (TOF) Time smearing Timing coincidence among the PMT hits for a 2.2 MeV  diluted by different TOFs

23. A proposed forced trigger logic

24. PMT hits in a given window 2.2 MeV  ’s 3.5kHz PMT dark noise assumed After TOF correction, 56% neutrons can be tagged with event Rate increase due to PMT dark noise less than 20Hz.

25. Goal for SRN search @SK-III 10-year with SK-I SRN signal: 22.7 Background: 115 10-year with SK-III SRN signal: 18 Background: 12 If we do not tag neutrons If we can tag neutrons with 80% efficiency and suppress BG by 90%. Relic model: S.Ando, K.Sato, and T.Totani, Astropart.Phys.18, 307(2003) with flux revise in NNN05. May lead to a discovery of SRN.

26. Tsinghua conditionally accepted by Super-K collaboration

27. Formally accepted in 2005 KAMIOKA OBSETVATORY INSTITUTE FOR COSMIC RAY RESEARCH, UNIVERSITY OF TOKYO Higashi-Mozumi, Kamioka-cho, Hida-city Gifu 506-1205, JAPAN TEL +81-578-5-9601, FAX +81-578-5-2121 e-mail: suzuki@suketto.icrr.u-tokyo.ac.jp 15-July, 2005 Shaomin Chen Center for High Energy Physics Tsinghua University Beijing 100084 P.R. of China Dear Professor Chen, We are happy to inform you that the Super-Kamiokande Collaboration Council decided to welcome the Tsinghua University group into the collaboration and appointed you as the team leader of Tsinghua neutrino physics group. Your interest in participating in the detector upgrade together with the relevant physics research programmes was well appreciated by the council. The council stressed the importance of establishing a close cooperation between the Center for High Energy Physics in Tsinghua University and Kamioka observatory, Institute for Cosmic Ray Research in University of Tokyo. We are very much looking forward to seeing a fruitful collaboration. Yours Sincerely Yoichiro Suzuki Spokesman of the Super-Kamiokande Collaboration

28. Tsinghua students at Kamioka Around ICRR research building “Kenkyu-tou” Inside the mine

29. Work has been done since then Work in last year Work in this year

30. Summary  Super-K starts a new life this year (SK-III)  Many physics researches can continue  Efforts made for lowering energy threshold and broad dynamic range  Tsinghua university has been a member of Super-K collaboration, making its effort in detecting supernova neutrinos.