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Atmospheric Neutrinos: Background for Proton Decay

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Atmospheric Neutrinos: Background for Proton Decay University of Torino, July 2, 2018 Takaaki Kajita Institute for Cosmic Ray Research, The Univ. of Tokyo 1 Outline • Kamiokande • Super-Kamiokande • Discovery of neutrino oscillations • Solar neutrino oscillations • Various oscillation studies • Detecting relic supernova neutrinos • Future neutrino experiment in Kamioka • Summary 2 Kamiokande 3 Proton decay experiments (1980’s) In the 1970’s, Grand Unified Theories, predicted that protons should decay with the lifetime of about 1030 years. Several proton decay experiments began in the early 1980’s. One of then was the Kamioaknde experiment. IMB Kamiokande (3300ton) (1000ton) KGF (100ton) NUSEX (130ton) Frejus (700ton) 4 Location of the Kamiokande experiment 5 Kamiokande construction team (Spring 1983) M. Takita TK A. Suzuki T.Suda M. Nakahata K. Arisaka M. Koshiba Y. Totsuka (2002 Nobel Prize) T. Kifune 6 Constructing the Kamiokande detector (Spring 1983) 7 Kamiokande The experiment began in July 1983. 8 Didn’t observe proton decays, but… Pulse height distribution for electrons from the decays of cosmic ray muons (early autumn 1983) Neutrinos with the energies of about 10 MeV could be observed. Improvement of the Kamiokande detector to observe solar neutrinos. Initial idea of Super-Kamiokande. (both by M. Koshiba) 9 Toward Kamiokande-II (1984-5) Construction of the bottom outer detector Construction of the side outer detector (between Detector improvement works the steel tank and the rock) during 1984 to 1986. 10 Water and the trigger rate Radioactivities (mostly Rn at that stage) was the most serious issue. Stable trigger rate after Jan. 1987. 11 SN1987A (Feb. 23, 1987) K. Hirata et al., Phys. Rev. Lett. 58 (1987) 1490. SN1987A (at LMC) Number of PMT hits @Anglo Australian Observatory (The IMB experiment also observed the neutrino signal.) 12 Atmospheric neutrinos: background for proton decay Cosmic ray Incoming cosmic rays Air nucleus Pion Muon Electron 2 muon- neutrinos 1 electron- neutrino © David Fierstein, originally published in Scientific American, August 1999 13 Atmospheric νµ deficit Proton decay experiments in the 1980’s observed many atmospheric neutrino events. Because atmospheric neutrinos are the most serious background to the proton decay searches, it was necessary to understand atmospheric neutrino interactions. During these studies, a significant deficit of atmospheric muon-neutrino (νµ) events was observed in Kamiokande (1988). K. Hirata et al, Phys.Lett.B 205 (1988) 416. Kamiokande Simulation (expectation) Muon-neutrino ミューニュートリノ events Data 計 Electron-neutrino 観 電子ニュートリノ events 0 50 100 150 14 Results from IMB on the νµ deficit D. Casper et al., PRL 66 (1991) 2561. R. Becker-Szendy, PRD 46 (1992) 3720. IMB experiment, which was another large water Cherenkov detector, also reported the deficit of νµ events (1991). Kamiokande (1988,92,94) （1991,92） 15 Neutrino oscillations If neutrinos have masses, neutrinos change their flavor (type) from one flavor (type) to the other. For example, oscillations could occur between νµ and ντ. Theoretically predicted by; Sakata Memorial Archival Library Probability: arXiv:0910.1657 νµ to remain νµ B. Pontecorvo Probability: S. Sakata, Z. Maki, M. Nakagawa νµ toντ L is the neutrino flight length (km), Wikipedia E is the neutrino energy (GeV). If neutrino mass is smaller, the oscillation length (L/E) gets longer. Atmospheric Neutrino Oscillations 16 Confirmation of solar νe deficit (1989) K. S. Hirata et al., Phys. Rev. Lett. 63 (1989) 16. The Kamiokande results on; Standard Solar Model • Supernova neutrinos (1987) • Atmospheric neutrino deficit (1988) • Solar neutrino deficit (1989) were evaluated to be very important. The construction of the Super- Kamiokande experiment was approved in 1991 by the (Other solar neutrinos experiments (SAGE, Gallex/GNO) in Japanese government. the 1990’s also confirmed the solar neutrino deficit.) 17 Super-Kamiokande 18 Super-Kamiokande detector 50,000 ton water Cherenkov detector (22,500 ton fiducial volume) About 20 times larger mass ~160 collaborators ４２ｍ ３９ｍ １０００ｍ underground 19 Initial idea of Super-Kamiokande (1983) In the fall of 1983, Prof. Koshiba recognized that solar neutrinos can be detected in Kamiokande. At the same time, he proposed Super- Kamiokande to study solar neutrinos in detail (and to search for proton decays). Initial drawing of the Super-Kamiokande detector (In “32 kton Water Cherenkov Detector (JACK) A proposal for detailed studies of nucleon decays and for low energy neutrino detection” by M. Koshiba, in Proceedings of workshop on Grand Unified Theories and Cosmology (Dec. 7-10, 1983, KEK, Tsukuba, Japan) 20 Beginning of the Super-Kamiokande collaboration between Japan and USA Y. Totsuka Y. Suzuki TK W. Kropp H. Sobel K. Nishikawa A. Suzuki @ Institute for K. Nakamura Cosmic Ray J. Arafune Research, 1992 J. Stone (ICRR director) 21 Constructing the Super-Kamiokande detector (spring 1995) Y. Totsuka 22 Filling water in Super-Kamiokande Jan. 1996 23 Discovery of neutrino oscillations 24 Fully automated analysis One of the limitation of the Kamiokande’s atmospheric neutrino analysis was the necessity of the event scanning for all data and Monte Carlo events, due to no satisfactory ring identification software. Hough transformation Multi Cherenkov ring event + maximum likelihood ν 25 Atmospheric neutrino events observed in Super-K Single Cherenkov Single Cherenkov ring electron ring muon Size = pulse height ν Color = time 26 What will happen if the νµ deficit is due to neutrino oscillations Not long enough Cosmic ray to oscillate Long enough to oscillate We should observe a deficit of upward going νµ’s! We needed much larger detector. Super-Kamiokande Cosmic ray 27 Evidence for neutrino oscillations (Super-Kamiokande @Neutrino ’98) Y. Fukuda et al., PRL 81 (1998) 1562 Super-Kamiokande concluded that the observed zenith angle dependent deficit (and the other supporting data) gave evidence for neutrino oscillations. 28 Solar neutrino oscillations 29 SNO 2km 1000 ton of heavy water 30 Evidence for solar neutrino oscillations SNO PRL 89 (2002) 011301 (A plot based on the SNO PRC 72, 055502 (2005) salt-phase data) Three (or four) different measurements intersect at a point. Evidence for (νµ+ντ) flux SSM 68%CL SNO NC 68%CL SNO CC SNO ES SK ES 68%CL 68%CL 68%CL 31 KamLAND (another experiment in Kamioka) KamLAND is a 1kton liquid scintillator exp. constructed at the location of Kamiokande. Many nuclear power stations around KamLAND at the distance of about 180 km. Long baseline reactor neutrino osc. experiment. 1kton liq. scintillator Reactors 32 Really neutrino oscillations ! KamLAND PRD 83 (2011) 052002 Energy spectrum of neutrinos from nuclear power stations observed in KamLAND. OR Really neutrino oscillations! 33 Various oscillation studies 34 Updating atmospheric neutrino data Super-K @Neutrino98 Super-K (2016) Super-K @Neutrino 2016 No oscillation νµντ oscillation Number of events plotted: 531 events 5932 events Detailed studies of oscillations! 35 Detecting tau neutrinos Super-K,arXiv:1711.09436 If the oscillations are between νµ and ντ, one should be able to observe ντ’s. A simulated ντ event. 36 It is not possible for Super-K to identify ντ events by an event by event bases. Statistical analysis τ-appearance at 4.6σ (consistent with OPERA) knowing that ντ’s are upward-going only. 36 Other contribution of Super-Kamiokande to neutrino physics Accelerator based long baseline neutrino oscillation experiments K2K experiment (1999 – 2004) T2K experiment (2010 -) Electron neutrino appearance (evidence Confirmation of neutrino for 3 flavor oscillation effect). oscillation with accelerator beam. 295km (Of course, there are other important long baseline experiments: MINOS, OPERA, NOvA. ) 37 Experiments for the third neutrino oscillations Accelerator based long baseline neutrino oscillation experiments NOν A MINOS T2K Reactor based (short baseline) neutrino oscillation experiments Daya Bay RENO Double Chooz 38 Discovery of the third neutrino oscillations (2011-2012) Accelerator based νe appearance experiments MINOS PRL 107 (2011) 181802 T2K PRL 107 (2011) 041801 Note: these data are those in 2011-2012. The updated data are much better (including those from NOvA). Reactor based anti-νe disappearance experiments Daya Bay PRL 108 (2012) 171803 RENO PRL 108 (2012) 191802 Double Chooz PRL 108 (2012) 131801 Tthe basic structure for 3 flavor neutrino oscillations has been understood! 39 Oscillation parameters P.F.de Salas et al.,arXiv:1708.01186 (v2) (April 2018) Review of Particle Physics (2017), K. Nakamura and S.T. Petcov, “14. Neutrino mass, mixing and oscillations” Information for Physics Beyond the See also, A. Marrone et al., AIP Conf.Proc. 1894 (2017) 020015 Standard Model (at very high energies) ! and many other references 40 Detecting relic supernova neutrinos 41 SN1987A (Feb. 23, 1987) SN1987A (at LMC) K. Hirata et al., Phys. Rev. Lett. 58 (1987) 1490. Number of PMT hits @Anglo Australian Observatory Super-Kamiokande has been waiting for the next nearby Supernova. No observation of Supernova neutrinos so far… 42 Supernova relic neutrinos Super-K Super-Kamiokande collab. would like to observe neutrinos produced by the Supernova explosion in the past Universe! Credit: NASA/WMAP Science Team 43 Detecting Supernova relic neutrinos + (M. Ikeda, neutrino 2018) νe + p e + n , n + Gd Gd + γ’s (total E of γ’s ~8MeV) Expected spectrum in SK-GD Gd capture eff. SRN flux: Horiuchi, Beacom and Dwek, 100[%]100 PRD, 79, 083013 (2009) 90 80 （ ） 0.2%80 Gd2(SO4)3 ~100t for SK σ: 10 years with SK-Gd gives70 90% neutron capture 6060 50 Total BG 4040 30 2020 4.3σ 10 2.5σ Capture on gadolinium [%] on gadolinium Capture 0 0 2.1σ 00 0.0020 0.020.02 0.20.2 10 12 14 16 18 20 22 24 26 28 GadoliniumGadolinium sulfate sulfate concentration[%] concentration [%] Position Energy (MeV) 44 Schedule of SK-Gd JFY (Neutrino 2018, M. Ikeda) Earliest possibility of Gd (0,02%) in Super-K will be late 2019. 45 Super-Kamiokande now 46 Future neutrino experiment in Kamioka 47 Hyper-K as a natural extension of water Ch.
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