Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
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 Kamiokande detector (1983 – 1996) neutrino Inner counter: 948 20-inch PMTs 16 m high, 15.6 m diameter Anti-counter 123 20-inch PMTs e 3000 ton water tank Photo-sensitive: 2140 t Fiducial volume: 680 t (for solar neutrino) Photocoverage: 20 % 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 History of Super-Kamiokande detector 1996 1997 1998 1999 2000 2001 2002 SK-I SK-I 11146 ID PMTs (40% coverage) Energy Threshold 5.0 MeV (total electron energy) 2003 2004 2005 2006 SK-II Acrylic (front) + FRP (back) SK-II 5182 ID PMTs (19% coverage) 7.0 MeV 2007 SK-III SK-III 11129 ID PMTs (40% coverage) 2008 2009 SK-IV SK-IV Electronics Upgrade 4.5 MeV < 4.0 MeV work in progress target Original purpose of Kamiokande Search for proton decay 3500 p0→gg e+ p→e+p0 Monte Carlo simulation High resolution detector for measuring the branching ratio of proton decay. It should be useful to pin down the true GUT model. 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 Advantage of Kamiokande as a “telescope” Advantage of Kamiokande as a “telescope” Directionality Imaging Cherenkov detector has excellent directionality. neutrino n+en+e electron Energy information The number of observed Cherenkov photon is proportional to energy of particle. Real time detection Real time counter experiment. Another advantage of Kamiokande: Particle identification(PID) electron Evis=540 - 1200 MeV Evis=270 - 540 MeV Evis=130 - 270 MeV muon Evis=80 - 130 MeV Evis=30 - 80 MeV Mis-identification is less than 1%. PID was very important for the atmospheric neutrino analysis. 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”. Solar neutrinos (Super-Kamiokande) May 31, 1996 – July 13, 2001 (1496 days ) Ee = 5.0 - 20 MeV n e- qsun 22400 solar n events (14.5 events/day) COSqsun flux : 2.35 0.02 0.08 [x 106 /cm2/sec] Data = 0.406 0.004 +0.014 (BP2004: 5.79 x 106 /cm2/sec) -0.013 SSM(BP2004) 8B 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 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 Excluded region by energy spectrum and day/night Super-Kamiokande 1496 days S.Fukuda et al., Phys. Lett. B 539 (2002) 179 Solar Neutrino future prospects in SK P(ne ne) ne survival probability (at best fit parameter) Transition from vacuum to matter osc. Upturn is expected in 8B spectrum. Aim to reduce background in SK ,IV ~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 Supernova at LMC (February 23, 1987) After Before SN1987A signal by Kamiokande It was when the Kamiokande detector was almost ready for solar neutrino detection. Visible energy (MeV) 11 events in 13 sec. Background level sec JT: 1987 Feb 23 16:35:35 (±1min) UT: 7:35:35 Time SN1987A: supernova at LMC(50kpc) Feb.23, 1987 at 7:35UT Kam-II (11 evts.) IMB-3 (8 evts.) Baksan (5 evts.) 24 events total IMB-3 Total Binding Energy Kamiokande-II from G.Raffelt BAKSAN 95 % CL Contours Theory _ Spectral ne Temperature 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 Super-K: Time variation measurement by ne+p Assuming a supernova at 10kpc. nep e+n events give direct energy information (Ee = En – 1.3MeV). Time variation of event rate Time variation of mean energy Enough statistics to discriminate models Super-K: Expected angular distribution n+e n+e ne+p ne+p n+e ne+p n+e ne+p Simulation of a SN at 10kpc 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. Neutrino flux and spectrum from Livermore simulation Supernova Relic Neutrinos S.Ando, Astrophys.J.607:20-31,2004. S.Ando, NNN05 Supernova Relic Neutrinos Reactor n (ne) Constant SN rate (Totani et al., 1996) Totani et al., 1997 Woosley, 1997 Solar 8B (ne) Hartmann, Malaney, 1997 Kaplinghat et al., 2000 Ando et al., 2005 Lunardini, 2006 Solar hep (ne) Fukugita, Kawasaki, 2003(dashed) SRN predictions (ne fluxes) Atmospheric ne 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) Large target mass like SK and high background reduction are necessary. Super-K results so far Flux limit VS predicted flux Energy spectrum of SK-I and SK-II (>18MeV) SK-I (1496days) Total background Atmospheric nm → invisible m → decay e Atmospheric nm → invisible m → decay e Events/4MeV 90% CL limit of SRN SK-II(791 days) Atmospheric ne Atmospheric ne Energy (MeV) Spallation background Observed spectrum is consistent with estimated background. Search is limited by the invisible muon background. Neutron tagging in water Cherenkov detector Neutron capture gamma ne n+Gd →~8MeV g n p DT = ~30 msec Add 0.2% GdCl3 in water (J.Beacom and M.Vagins) Phys.Rev.Lett.93:171101,2004 e+ Gd g Positron and gamma ray vertices are within ~50cm. ne can be identified by delayed coincidence. 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.) 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-like ratio is 60% of expectation. Atomospheric anomaly in Kamiokande Zenith angle distribution of multi-GeV events (1994) Y.Fukuda et al., Phys. Lett. B 335 (1994) 237. upward downward Zenith Angle distribution of SK cos θzenith \ cos θzenith cos θzenith SK-I data Monte Carlo (no oscillations) Monte Carlo (best fit oscillations) 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. 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) 3 flavor analysis: SK-I + SK-II Normal Hierarchy preliminary Inverted Hierarchy Note: one mass scale dominance method(dm212 is set to 0) Full 3-flavor analysis is being prepared. SK-IV electronics: New front-end electronics, QBEE Network Interface Card QTC-Based Electronics with Ethernet (QBEE) Ethernet Readout 24 channel input QTC (custom ASIC) 60MHz Clock 3 gain stages TDC Trigger Wide dynamic range(>2000pC) PMT signal factor 5 larger than old electronics Pipe line processing QTC TDC Calibration Pulser FPGA multi-hit TDC (AMT3) FPGA Ethernet Readout 60MHz common system clock Internal calibration pulser Low power consumption ( < 1W/ch ) Difference in readout system Former readout system 12PMT signals per module Former Electronics (ATM) HITSUM Trigger (1.3msec x 3kHz) Trigger logic Readout (backplane, SCH, SMP) Hardware Trigger using number of hit (HITSUM) 1.3msec event window New readout system No hardware trigger. All hits are readout. Apply software trigger. 24PMT signals per module New Electronics (QBEE) Periodic trigger (17msec x 60kHz) Clock Readout (Ethernet) Collect ALL hits every 17msec time window. The 60kHz clock synchronize time of hit information. Variable event window by software trigger Performance of new electronics for supernova burst # of hits Performance for high rate Distance to SN vs. number of events input output burst hit rate (kHz) Dead time free in the new system 130kHz 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 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.