M.Nakahata. Kamioka observatory ICRR/IPMU, Univ. of Tokyo. 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 1

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1 Neutrino experiments years at Kamioka -- M.Nakahata Kamioka observatory ICRR/IPMU, Univ. of Tokyo 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 1

2 Contents Current experiments at Kamioka History of neutrino experiments at Kamioka Recent highlights from Super-K Future of Super-K, and Hyper-K project Future /11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 2

3 Kamioka underground experiments (NOW) m Mt. Ikeno-yama KamLAND (Tohoku Univ.) 1000ton liquid scintillator detector Rector, geo neutrinos 136 Xe double beta decay Super-Kamiokande 50,000 ton water Cherenkov detector Atmospheric, solar, supernova neutrinos Proton decay, indirect dark matter search Far detector for T2K CANDLES CaF 2 scintillation detector for 48 Ca double beta decay KamLAND (old Kamiokande site) Lab.A Super-K dome Gravitational-wave CLIO 100m x 100m prototype Geo-physics 100m x 100m Laser strainmeter XNASS Direct dark matter search experiment Gd test water system clean room NEWAGE Direction dark matter experiment

4 Kamioka underground experiments (NOW) Mt. Ikeno-yama KAGRA KAGRA Laser strainmeter center area KAGRA Gravitational-wave Telescope 1.5km Geophysics interferometer 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 4

5 Kamiokande-I detector( ) 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 5 Original purpose: Search for proton decay Inner detector only. Readout of charge information only (i.e. no timing information). Fiducial volume: 880 ton (2m from the wall) inch PMTs were used Photo-coverage: 20%

6 Competitor: IMB experiment 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 6 Fiducial volume: ~3400 ton (x4 of Kamioande) inch PMTs Photo-coverage: 1.3% Already started from 1982

7 Purpose of Kamiokande Aimed to measure branching ratio of proton decay 3500 π 0 γγ e + p e + π 0 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. 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 7

8 Particle identification(pid) of e/µ for proton decay electron E vis = MeV E vis = MeV E vis = MeV muon E vis = MeV E vis =30-80 MeV Mis-identification is less than 1%. But, proton decay was not observed. 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 8

9 Upgrade to Kamiokande-II ( ) Thanks to large photo-coverage, it was found that the detector is sensitive to low energy events. So, the detector was upgraded for solar neutrinos in Upgrade electronics for readout of timing information. It improved vertex reconstruction. Made outer detector to shield external gamma rays 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 9

10 SN1987A: a supernova at LMC (Feb.23 rd, 1987) It happened when the Kamiokande detector was almost ready for solar neutrino measurement. Visible energy (MeV) Background level 11 events in 13 sec. After Before JT: 1987 Feb 23 16:35:35 (±1min) UT: 7:35:35 sec Total energy released by ν e was measured to be ~5x10 52 erg. It was consistent with core-collapse scenario of supernova. 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 10

11 1988: First observation of solar neutrinos Based on 450 days Kamiokande data taken from Jan.1987 to May 1988 SSM prediction Observed number of solar neutrinos was about 50. It was almost half of the expectation from the Standard Solar Model (SSM) and confirmed the solar neutrino problem. K.S.Hirata et al., Phys. Rev. Lett. 63(1989) /11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 11

12 1988: Atmospheric neutrino anomaly at Kamiokande Data in 1988 paper (Phys. Lett. B205 (1988)416. ) Electron-like Muon-like prediction data Electron-like data is consistent with prediction. But, muon-like data is 59±7% of prediction. The first hint of neutrino oscillations. 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 12

13 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 13 Super-Kamiokande detector (1996 ) In order to solve the problems of solar and atmospheric ν and detect more supernova ν. 50,000 t water tank (42m high, 40m diameter) 32,000 t photo-sensitive volume 22,000 t fiducial volume 11, inch PMTs Photo-coverage: 40% (x2 of Kamiokande in order to lower energy threshold) 1000m underground in Kamioka mine X 25 fiducial volume than Kamiokande

14 1998: Evidence for atmospheric neutrino oscillation Cosmic rays produce neutrinos. P + A N + π ± + X µ ± ( ) + ν µ e ± ( ) + ν e + ( ν ) µ Super-Kamiokande ν µ ν τ 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka Kajita s presentation in Neutrino 1998 conference. ν µ disappearance 14

15 2001: Evidence for solar neutrino oscillation 2001 SNO paper SK ES vs. SNO CC ν µ/τ flux (10 6 /cm 2 /sec) Interactions (ES) ν+ e - ν + e - (σ of ν µ/τ is 1/7 of ν e ) (CC) ν e + d p + p + e - (NC) ν x + d ν x + p + n (X=e,µ,τ) ν e flux (10 6 /cm 2 /sec) ν e to ν µ/τ conversion 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 15

16 2002: Reactor neutrino oscillation by KamLAND KamLAND 70GWatt power(7% of world total) was generated by reactors in km from Kamioka. KamLAND Built at old Kamiokande site 1000 ton liquid scintillator. Run by Tohoku University. ν e disappearance 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 16

17 :K2K (KEK to Kamioka) The first artificial neutrino beam experiment in the world. 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 17

18 Results from K2K experiment N obs sk N pred sk All ring µ-like e-like multi-ring No oscillation Oscillation m 2 (ev 2 ) Confirmed atmospheric oscillation (ν µ disappearance due to m 2 23/θ 23 ) using an artificial beam. sin 2 2θ 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 18

19 From 2009: T2K (Tokai to Kamioka) Super-Kamiokande T2K(2009~) 40m J-PARC produces high intensity neutrino beam. SK detects neutrinos at 295km. Off-axis beam technique was adopted to make narrow band neutrino beam. 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 19

20 History of double beta decay at Kamioka ELEGANT V( 100 Mo, 116 Cd) , hosted by Osaka Univ.(Ejiri et site 136 Xe ELEGANT III ( 76 Ge) , hosted by Osaka Univ.(Ejiri et site ELEGANT IV( 100 Mo) , hosted by Osaka Univ.(Ejiri et site CANDLES III ( 48 Ca) , hosted by Osaka Univ. (Kishimoto et Lab.C KamLAND-zen , hosted by Tohoku Univ. (Inoue et site 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 20

21 Recent Highlights from SK (including T2K results) 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 21

22 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 22 SK atmospheric ν: ντ appearance Published at PRL 110, (2013) ν µ ν τ Threshold ~3.5GeV ν τ τ hadrons Search for events consistent with hadronic decay of τ lepton Multi-ring e-like events with visible energy above 1.3GeV. Negligible primary ν τ flux so ν τ must be oscillation-induced: upward-going Observed # / Expected # =1.47+/-0.32 (4.6σ from 0) assuming NH

23 SK atmospheric ν analysis (with T2K constraint) Not a joint analysis, fit external data using publicly available T2K info. m 2 32 m 2 13 sin 2 θ 23 Inverted Normal preliminary δ CP ev 2 Fit (585 dof) χ 2 sin 2 θ 13 δ CP sin 2 θ 23 m 2 32 ev 2 SK+T2K (IH) (fix) x10-3 SK+T2K (NH) (fix) x10-3 SK+T2K (θ 13 fixed): χ 2 = χ 2 NH-χ 2 IH = -5.2 (-3.8 exp. for SK best, -3.1 for combined best) Under IH hypothesis, the probability to obtain χ 2 of -5.2 or less is (sin 2 θ 23 =0.6) and (sin 2 θ 23 =0.4). 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 13

24 SK solar ν: day/night effect A ( Day Night) = DN ( Day + Night) / 2 D/N asymmetry (A DN ) Δm 2 21=4.84x10-5 ev 2 SK-I -2.0±1.8±1.0% SK-II -4.4±3.8±1.0% SK-III -4.2±2.7±0.7% SK-IV -3.6±1.6±0.6% combined -3.3±1.0±0.5% Solar global analysis ~2σ diff. in m 2 12 Green: Solar global dashed only SK+SNO Blue: KamLAND Red: Solar+KamLAND non-zero significance 3.0σ Data / MC(unoscillated) Direct indication of matter effect. SK solar ν: spectrum (total # of bins 83) χ 2 Solar+KamLAND ~2σ worse Solar Flat Prob Electron kinetic energy (MeV) 24

25 Latest results from T2K J.Imber in Session VII ν e appearance for the study of θ 13 and δcp ν µ disappearance for the study of θ 23 & m 2 23 Until May x POT (~20% of the planned total) Neutrino mode 7.57x10 20 POT Anti-Neutrino mode 7.53x10 20 POT (POT: Proton On Target) Recovery from the earthquake Accelerator stopped due to an accident 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 25

26 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 26 T2K: ν µ disappearance and ν e appearance data ν µ 7.57x10 20 POT, ν µ 7.53x10 20 POT data ν µ events 135 ν e events 32 ν µ events 66 ν e events 4

27 T2K: results from ν µ +ν µ disappearance ν µ 7.57x10 20 POT, ν µ 7.53x10 20 POT data Oscillation parameters of sin 2 θ 23 and m 2 32 compared with others Best fit values: (sin 2 (θ 23 ), m 2 32 )= (0.532, (ev 2 )) T2K has given the most previse measurement. T2K favors maximal mixing (sin 2 θ 23 =0.5) but NOvA disfavors. Need more data to conclude. 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 27

28 T2K: Results on δcp from ν e +ν e appearance ν e events(data) 32 ν ē events(data) 4 Expectation(δCP=0) 24 Expectation(δCP=0) 7 δcp = [-3.13, -0.39] (NH), [-2.09, -0.74] CL The best fit points lie near the maximally CP violating value δcp=-0.5π. The CP conserving values (δcp=0 and δcp= π) lying outside of the T2K 90% confidence level interval. Interesting to proceed. Towards T2K-II 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka J.Imber in Session VII 28

29 Future of Super-K, and Hyper-K project 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 29

30 Identify ν e p events by neutron tagging with Gadolinium. Gadolinium has large neutron capture cross section and emit 8MeV gamma cascade. ν e p e + n SK-Gd project Gd 8 MeV γ cascade Captures on Gd 100% 80% 60% 0.1% Gd gives ~90% efficiency for n capture In Super-K this means ~100 tons of water soluble Gd 2 (SO 4 ) 3 ΔT~30μs Vertices within 50cm 40% 20% 0% % 0.001% 0.01% 0.1% 1% Gd in Water 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 30

31 SRN prediction (ν e fluxes) Physics with SK-Gd Supernova Relic Neutrinos (SRN) Open widow for SRN at 10-30MeV Expected event rate events/year/22.5kt(10-30mev) Study supernova rate from the beginning of universe. Averaged energy spectrum. Improve pointing accuracy for supernova bursts, e.g. 4~5 3 (90%C.L.) for 10kpc Simulation of a 10kpc supernova νe+p ν+e Discriminate proton decay (essentially no neutron) and atmospheric neutrino background(with neutrons). Neutrino/anti-neutrino identification. Precise measurement of θ 12 and m 2 21 by reactor neutrinos. 31

32 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 32 Kamiokande 880 ton fiducial / 3000 ton total water Cherenkov detector X ~25 times Super-Kamiokande 22,500 ton fiducial / 50,000 total water Cherenkov detector X ~20 times Hyper-Kamiokande 190,000x2 ton fiducial / 260,000x2 total water Cherenkov detector Physics at Hyper-K: J. Kameda in Session VIII

33 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 33 Japanese saying: 3 度目の正直. The third time s the charm. My translation Proton decay will be observed in the third generation experiment.

34 Future++ (my personal view) 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 34

35 Future++ A larger volume detector(hyper-k) would start ~10years from now. (Hope to) Observe SRN at SK within ~10 years from now. What physics SK-site (50,000m 3 ) can do after that? Are neutrinos Majorana particles? Double Beta Decay (DBD) is the unique method to verify that. So, DBD is very important. Yanagida-san said DBD is more important than proton decay. As I presented, SK atmospheric ν indicates normal hierarchy. Initial indications have been always true so far at Kamioka (unfortunately). So, let s think about very big DBD detector to reach normal hierarchy. 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 35

36 Future++ Towards 2-3 mev What about this? Forget about it. Neutrino parameters are always lucky. 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 36

37 Future++ What is τ 1/2 of 0νββ for 2.5 mev? τ 1/2 = 1.8 x 10^{29} years for 136 Xe (QRPA-B, g A =1.269) τ 1/2 = 2.1 x 10^{29} years for 48 Ca (IBM-2, g A =1.269) (Many thanks to T.Iida-san and I.Shimizu-san for various information) How much weight is necessary to detect one 0νββ event/year? 59 tons of 136 Xe (~20m 3 liquid Xe, ~10,000m 3 1atm. gas Xe) 24 tons of 48 Ca Remark: solar neutrino background (next page) 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 37

38 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 38 Solar Neutrino background 136 Xe 48 Ca ~0.1 8 B solar neutrino events/year for 10keV window for 59 tons Xe Today's signal is tomorrow's background.

39 Future++ What is τ 1/2 of 0νββ for 2.5 mev? τ 1/2 = 1.8 x 10^{29} years for 136 Xe (QRPA-B, g A =1.269) τ 1/2 = 2.1 x 10^{29} years for 48 Ca (IBM-2, g A =1.269) (Many thanks to T.Iida-san and I.Shimizu-san for various information) How much weight is necessary to detect one 0νββ event/year? 59 tons of 136 Xe (~20m 3 liquid Xe, ~10,000m 3 1atm. gas Xe) 24 tons of 48 Ca Remark: solar neutrino background (next page) So, good energy resolution is necessary. Also, for separating from 2νββ. Let s think about possible techniques (high resolution, tracking, tagging ββ decay products.) 2016/11/8 M. Nakahata: Neutrino experiments - 30 years at Kamioka 39

40 Conclusions More than 30 years have passed since we started experiments at Kamioka. Neutrino oscillations have been established in the last 30 years. There are still many important unknowns in neutrino physics. Future developments are expected. Let s enjoy neutrino physics! 40