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M.Nakahata Kamioka observatory, ICRR, IPMU, Univ. of Tokyo

Kamiokande and Super- Kamiokande Results on Neutrino Astrophysics. M.Nakahata Kamioka observatory, ICRR, IPMU, Univ. of Tokyo. Professor Yoji Totsuka (1942-2008). Kamiokande spokesman: 1987 April ---- end. Super-Kamiokande spokesman: beginning ---- 2002.

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M.Nakahata Kamioka observatory, ICRR, IPMU, Univ. of Tokyo

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  1. Kamiokande and Super-Kamiokande Results on Neutrino Astrophysics M.Nakahata Kamioka observatory, ICRR, IPMU, Univ. of Tokyo

  2. Professor Yoji Totsuka (1942-2008) Kamiokande spokesman: 1987April ---- end Super-Kamiokande spokesman: beginning ---- 2002

  3. Kamiokande detector (1983 – 1996) 16 m high, 15.6 m diameter Inner counter: 948 20-inch PMTs neutrino Anti-counter 123 20-inch PMTs e 3000 ton water tank Photo-sensitive: 2140 t Fiducial volume: 680 t (for solar neutrino) Photocoverage: 20 %

  4. Super-Kamiokande detector (1996 – ) • 50000 t water tank (42m high, 40m diameter) 32000 t photo-sensitive volume 22000 t fiducial volume • 11146 20-inch PMTs • Photocoverage: 40% • 1000m underground in Kamioka mine X 30 fiducial volume than Kamiokande

  5. History of Super-Kamiokande detector SK-I SK-II SK-III SK-IV SK-I SK-II SK-III SK-IV Acrylic (front) + FRP (back) 11146 ID PMTs (40% coverage) 5182 ID PMTs (19% coverage) 11129 ID PMTs (40% coverage) Electronics Upgrade Energy Threshold (total electron energy) 5.0 MeV 7.0 MeV 4.5 MeV work in progress < 4.0 MeV target

  6. Original purpose of Kamiokande Search for proton decay 3500 p0→gg e+ High resolution detector for measuring the branching ratio of proton decay. It should be useful to pin down the true GUT model. p→e+p0Monte Carlo simulation

  7. Low energy neutrino detection It was found that the large photo-collection efficiency is useful also for detecting low energy neutrino. An event at Kamiokande Reconstructed energy = 19.8 MeV

  8. Advantage of Kamiokande as a “telescope”

  9. Advantage of Kamiokande as a “telescope” • Directionality • Imaging Cherenkov detector has excellent directionality. • Energy information • The number of observed Cherenkov photon is proportional to energy of particle. • Real time detection • Real time counter experiment. neutrino n + e  n + e electron

  10. Another advantage of Kamiokande: Particle identification(PID) electron Evis=540 - 1200 MeV Evis=270 - 540 MeV Evis=130 - 270 MeV Evis=80 - 130 MeV muon Evis=30 - 80 MeV Mis-identification is less than 1%. PID was very important for the atmospheric neutrino analysis.

  11. First solar neutrino plot at Kamiokande K.S.Hirata et al., Phys. Rev. Lett. 63(1989) 16 Jan,1987 --- May, 1988 (450 days) Solar model prediction Observed number of solar neutrino events was ~50. Confirmed the “solar neutrino problem”.

  12. Solar neutrinos (Ｓｕｐｅｒ－Ｋａｍｉｏｋａｎｄｅ) n e- qsun May 31, 1996 – July 13, 2001 (1496 days ) Ee = 5.0 - 20 MeV 22400 solar n events (14.5 events/day) COSqsun Data 8B flux : 2.35  0.02  0.08[x 106 /cm2/sec] +0.014 = 0.406 0.004 -0.013 SSM(BP2004) (BP2004: 5.79 x 106 /cm2/sec)

  13. Combined analysis of SK, SNO CC and NC 8B solar neutrino ne flux and (nm+nt) flux SSM prediction(1s) SNO NC SNO CC SNO ES SK ES Evidence for neutrino oscillation

  14. Solar neutrino energy spectrum Kamiokande II and III (2079 days ) Based on ~600 solar n events Super-Kamiokande (1496 days ) Based on ~22400 solar n events 5

  15. Excluded region by energy spectrum and day/night Super-Kamiokande 1496 days S.Fukuda et al., Phys. Lett. B 539 (2002) 179

  16. Solar Neutrino future prospects in SK Aim to reduce background in SK ne survival probability (at best fit parameter) Transition from vacuum to matter osc. Upturn is expected in 8B spectrum. ,IV P(ne ne) ~70% reduction below 5.5MeV and lower threshold to 4MeV Vacuum osc. dominant matter dominant Expected spectrum distortion with 5 years low BG SK data pp 7Be 8B

  17. Supernova at LMC (February 23, 1987) After Before

  18. SN1987A signal by Kamiokande It was when the Kamiokande detector was almost ready for solar neutrino detection. 11 events in 13 sec. Visible energy (MeV) Background level sec Time JT: 1987 Feb 23 16:35:35 (±1min) UT: 7:35:35

  19. SN1987A: supernova at LMC(50kpc) 95 % CL Contours Kamiokande-II IMB-3 BAKSAN Feb.23, 1987 at 7:35UT Kam-II (11 evts.) IMB-3 (8 evts.) Baksan (5 evts.) 24 events total Total Binding Energy Theory _ Spectral neTemperature from G.Raffelt

  20. Super-K: Expected number of events Neutrino flux and energy spectrum from Livermore simulation (T.Totani, K.Sato, H.E.Dalhed and J.R.Wilson, ApJ.496,216(1998)) ~7,300 ne+p events ~300 n+e events ~360 16O NC g events ~100 16O CC events (with 5MeV thr.) for 10 kpc supernova

  21. Super-K: Time variation measurement by ne+p Assuming a supernova at 10kpc. nep e+nevents give direct energy information (Ee = En – 1.3MeV). Time variation of event rate Time variation of mean energy Enough statistics to discriminate models

  22. Super-K: Expected angular distribution ne+p ne+p ne+p ne+p Simulation of a SN at 10kpc n+e n+e Direction of supernova can be determined with an accuracy of ~5 degree. Spectrum of n+e events can be statistically extracted using the angular distributions. n+e n+e Neutrino flux and spectrum from Livermore simulation

  23. Supernova Relic Neutrinos S.Ando, Astrophys.J.607:20-31,2004. S.Ando, NNN05

  24. Supernova Relic Neutrinos Reactor n (ne) Constant SN rate (Totani et al., 1996) Totani et al., 1997 Hartmann, Woosley, 1997 Malaney, 1997 Kaplinghat et al., 2000 Ando et al., 2005 Lunardini, 2006 Fukugita, Kawasaki, 2003(dashed) Solar 8B (ne) Solar hep (ne) SRN predictions (ne fluxes) Expected number SRN events 0.8 -5.0 events/year/22.5kton (10-30MeV) (0.3 -1.9 events/year/22.5kton for 18-30MeV) Atmosphericne Large target mass like SK and high background reduction are necessary.

  25. Super-K results so farFlux limit VS predicted flux

  26. Energy spectrum of SK-Iand SK-II(>18MeV) SK-I (1496days) SK-II(791 days) 90% CL limit of SRN Total background Atmosphericnm → invisible m → decay e Atmospheric nm → invisible m → decay e Events/4MeV Energy (MeV) Atmosphericne Atmosphericne Spallation background Observed spectrum is consistent with estimated background. Search is limited by the invisible muon background.

  27. Neutron tagging in water Cherenkov detector ne can be identified by delayed coincidence. Neutron capture gamma n+Gd →~8MeV g n ne DT = ~30 msec p Add 0.2% GdCl3 in water (J.Beacom and M.Vagins) Phys.Rev.Lett.93:171101,2004 Gd e+ g Positron and gamma ray vertices are within ~50cm.

  28. Possibility of SRN detection Relic model: S.Ando, K.Sato, and T.Totani, Astropart.Phys.18, 307(2003) with flux revise in NNN05. If invisible muon background can be reduced by neutron tagging SK10 years (e=67%) Assuming invisible muon B.G. can be reduced by a factor of 5 by neutron tagging. Assuming 67% detection efficiency. By 10 yrs SK data, Signal: 33, B.G. 27 (Evis =10-30 MeV) We are studying feasibility of introducing gadolinium. (effect on water transparency, corrosion, cable connectors and etc.)

  29. Atmospheric neutrino anomaly in Kamiokande Paper in 1988 Initial hint m→e decay ratio EXPERIMENTAL STUDY OF THE ATMOSPHERIC NEUTRINO FLUX.KAMIOKANDE-II Collaboration (K.S. Hirata et al.), Phys.Lett.B205:416,1988 Momentum of single ring events e m Data from 1983 to1985 Small m→e decay ratio m-like/e-likeratio is 60% of expectation.

  30. Atomospheric anomaly in Kamiokande Zenith angle distribution of multi-GeV events(1994) Y.Fukuda et al., Phys. Lett. B 335 (1994) 237. upward downward

  31. Zenith Angle distribution of SK cos θzenith SK-I data Monte Carlo (no oscillations) Monte Carlo (best fit oscillations) \ cos θzenith cos θzenith

  32. Zenith Angle Analysis: SK-I + SK-II Best fit: Δm2 = 2.1 x 10-3 eV2 sin2 2θ = 1.02 χ2 = 830.1 / 745 d.o.f.

  33. L/E Analysis: SK-I + SK-II Datasets SK-I FC/PC μ-like: 1489 days SK-II FC/PC μ-like: 799 days Use only event categories with good L/E resolution: Partially-contained muons Fully-contained muons χ2 fit to 43 bins of log10(L/E) with 29 systematic error terms Compare against: Neutrino decoherence (5.0σ) Neutrino decay (4.1σ)

  34. 3 flavor analysis: SK-I + SK-II preliminary Normal Hierarchy Inverted Hierarchy Note: one mass scale dominance method(dm212 is set to 0) Full 3-flavor analysis is being prepared.

  35. SK-IV electronics: New front-end electronics, QBEE Network Interface Card QTC-Based Electronics with Ethernet (QBEE) • 24 channel input • QTC (custom ASIC) • 3 gain stages • Wide dynamic range(>2000pC) factor 5 larger than old electronics • Pipe line processing • multi-hit TDC (AMT3) • FPGA • Ethernet Readout • 60MHz common system clock • Internal calibration pulser • Low power consumption ( < 1W/ch ) Ethernet Readout PMT signal 60MHz Clock TDC Trigger Calibration Pulser QTC TDC FPGA

  36. Difference in readout system Former readout system HITSUM Hardware Trigger using number of hit (HITSUM) Former Electronics (ATM) Trigger logic Trigger (1.3msec x 3kHz) 12PMT signals per module 1.3msec event window Readout (backplane, SCH, SMP) New readout system No hardware trigger. All hits are readout. Apply software trigger. Collect ALL hits every 17msectime window. The 60kHz clock synchronize time of hit information. New Electronics (QBEE) Periodic trigger (17msec x 60kHz) Clock 24PMT signals per module Variable event window by software trigger Readout (Ethernet)

  37. Performance of new electronics for supernova burst Performance for high rate Distance to SN vs. number of events input # of hits output Dead time free in the new system 130kHz burst hit rate (kHz) • 100% efficiency up to 130kHz for each channel. • It corresponds to ~1000 x supernova at galactic center.(100 times better than previous system.) Previous system  Dead time free even for a supernova as close as 0.3kpc

  38. Conclusion • Neutrino astronomy was born in Kamiokande. And it was evolved in Super-Kamiokande. • KAM observed deficit of solar neutrinos, and SK contributed to the evidence for the solar neutrino oscillation and parameter determination. • Neutrinos from SN1987A by KAM, and a large statistical observation of galactic supernova is expected in SK. • Atmospheric neutrino anomaly in KAM, and evidence for atmospheric neutrino oscillation in SK. Detailed analysis is going on in SK. • The flux upper limit of supernova relic neutrinos is close to the theoretical expectation. SK is studying possibility of neutron tagging by gadolinium. • New electronics and online system was installed in September 2008 at SK, and SK-IV is running. • T2K will start soon (from April 2009). • More physics outputs are expected at SK.

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