KamLAND: Status and Prospects. Neutrino Geoscience 2010 Oct. 7, 2010 I. Shimizu (Tohoku Univ.)

Transkrypt

1 KamLAND: Status and Prospects Neutrino Geoscience 1 Oct. 7, 1 I. Shimizu (Tohoku Univ.)

2 KamLAND Collaboration A. Gando,1 Y. Gando,1 K. Ichimura,1 H. Ikeda,1 K. Inoue,1, Y. Kibe,1, Y. Kishimoto,1 M. Koga,1, Y. Minekawa,1 T. Mitsui,1 T. Morikawa,1 N. Nagai,1 K. Nakajima,1 K. Nakamura,1, K. Narita,1 I. Shimizu,1 Y. Shimizu,1 J. Shirai,1 F. Suekane,1 A. Suzuki,1 H. Takahashi,1 N. Takahashi,1 Y. Takemoto,1 K. Tamae,1 H. Watanabe,1 B.D. Xu,1 H. Yabumoto,1 H. Yoshida,1 S. Yoshida,1 S. Enomoto,, y A. Kozlov, H. Murayama,, 3 C. Grant,4 G. Keefer,4, z A. Piepke,, 4 T.I. Banks,3 T. Bloxham,3 J.A. Detwiler,3 S.J. Freedman,, 3 B.K. Fujikawa,, 3 K. Han,3 R. Kadel,3 T. OʼDonnell,3 H.M. Steiner,3 D.A. Dwyer,5 R.D. McKeown,5 C. Zhang,5 B.E. Berger,6 C.E. Lane,7 J. Maricic,7 T. Miletic,7, x M. Batygov,8, { J.G. Learned,8 S. Matsuno,8 M. Sakai,8 G.A. Horton-Smith,, 9 K.E. Downum,1 G. Gratta,1 Y. Efremenko,, 11 O. Perevozchikov,11, H.J. Karwowski,1 D.M. Markoff,1 W. Tornow,1 K.M. Heeger,, 13 and M.P. Decowski, 14 1Research Center for Neutrino Science, Tohoku University, Sendai , Japan Institute for the Physics and Mathematics of the Universe, Tokyo University, Kashiwa , Japan 3Physics Department, University of California, Berkeley, and Lawrence Berkeley National Laboratory, Berkeley, California 947, USA 4Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487, USA 5W. K. Kellogg Radiation Laboratory, California Institute of Technology, Pasadena, California 9115, USA 6Department of Physics, Colorado State University, Fort Collins, Colorado 853, USA 7Physics Department, Drexel University, Philadelphia, Pennsylvania 1914, USA 8Department of Physics and Astronomy, University of Hawaii at Manoa, Honolulu, Hawaii 968, USA 9Department of Physics, Kansas State University, Manhattan, Kansas 6656, USA 1Physics Department, Stanford University, Stanford, California 9435, USA 11Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA 1Triangle Universities Nuclear Laboratory, Durham, North Carolina 778, USA and Physics Departments at Duke University, North Carolina Central University, and the University of North Carolina at Chapel Hill 13Department of Physics, University of Wisconsin, Madison, Wisconsin 5376, USA 14Nikhef, Science Park 15, 198 XG Amsterdam, the Netherlands

3 KamLAND Experiment Earth Anti-Neutrino Detector Reactor Inner tank 1, ton LS Outer water tank 34% photo-coverage with and 554 PMTs Kamioka ~ 18 km baseline flavor neutrino oscillation most sensitive region P (ν e ν e )=1 sin θ sin ( 1.7Δm [ev ]l[m] ) E[MeV] Δm =(1/1.7) (E[MeV]/L[m]) (π/) ev reactor neutrino : sensitive to LMA solution geo neutrino : U and Th decays inside the Earth

4 KamLAND Kamioka Liquid Scintillator Anti-Neutrino Detector 1, ton Liquid Scintillator inverse beta-decay γ e + ν e p mean capture time ~ μsec on proton prompt γ n Pseudocumene (%) Dodecane (8%) PPO (1.5 g/l) delayed γ 1,35 17 inch inch PMTs commissioned in February, 3 photocathode coverage : % 34% Water Cherenkov Outer Detector

5 Physics Target in KamLAND observed energy (MeV) solar neutrino geo neutrino reactor neutrino supernova neutrino Jun. 1 preliminary new result Sep. 1 new result (hep-ex/ ) solar neutrino ν x e - ν x reactor neutrino geo neutrino γ e + ν e p prompt γ delayed e - mean capture time ~ μsec on proton n γ neutrino detection by electron scattering anti-neutrino detection by inverse beta-decay

6 Geologically Produced Antineutrinos Antineutrino Flux Number of anti-neutrinos per MeV per parent U series 3 Th series beta-decay Anti-neutrino energy, E (MeV) 38 U 6 Pb+8 4 He+6e +6 ν e MeV (1%) 3 Th 8 Pb He+4e +4 ν e +4.7 MeV (1%) 4 K 4 Ca + e + ν e MeV (89.8%) 4 K+e 4 Ar + ν e +1.51MeV(1.7%) 4 K Window for KamLAND

7 UCC U :.8 ppm / Th : 1.7 ppm MCC U : 1.6 ppm / Th : 6.1 ppm LCC U :. ppm / Th : 1. ppm continental crust Reference Earth Model Rudnick et al. (1995) oceanic crust U :.1 ppm / Th :. ppm chondrite meteorite { mantle U :.1 ppm / Th :.48 ppm { core Th/U ~ 3.9 radiogenic heat ~ 16 TW U : ppm / Th : ppm no U/Th in core Mantle = BSE (Primitive Mantle) Crust

8 Cumulative flux (1/cm /sec) Distance and Cumulative Flux sediment crust mantle total Distance from KamLAND (km) neutrino oscillation km P (E,L) 1 1 sin θ 1 Total Crust Mantle 5% of the total flux originates within 5 km Sediment (constant suppression) Percentage of total (%)

9 Radio-purity Upgrade in Geo Neutrino Purification system in Kamioka mine in 6 LS distillation ~ 1.5 kilo-liter / hour Events /.17MeV KamLAND 5 16 TW U/Th 1 B.G. total (α, n) 5 accidental Th Events /.17MeV Anti-neutrino energy, E (MeV) Anti-neutrino energy, E (MeV) 5 reactor α-source Distillation 1 Pb (Bi, Po), 4 K, 38 U, 3 Th,... N purge 85 Kr, 39 Ar,... U remove (α, n) BG to get higher S/N

10 Purification Process Top filling case in nd purification LS filling purification system 1st purification : Apr. 17, 7 ~ Aug. 1, 7 nd purification : Jun. 19, 8 ~ Feb. 9, 9 purified volume 1699 m m 3 ~5.6 times circulation in total In the nd purification, we succeeded in keeping the LS boundary by the precise density control

11 events/5kev/α-decay C(α, n) 16 O α natural abundance 1.1% 1 Po Q =.MeV 13 C 1 C n 16 O prompt γ (4.4MeV) 1 C(n, nγ) 1 C KamLAND data ground state e + e + + Background Estimation prompt γ (6.1MeV) or e + e - (6.MeV) recoil proton 16 p O delayed n γ (.MeV) kev(nd excited state) kev(1st excited state) γ O (MeV) E visible d 1st excited state nd excited state. kev( ) * kev γ C(n,n) C 6.13MeV MeV + in-situ calibration with 1 Po 13 C + LS purification 1st nd 7. 5 ~ 8. 7 ~ 1 Po 14 Bi 85 Kr (1) dominant BG source (α, n) has been reduced by down to ~ 1 / () determination of the cross section is improved by in-situ calibration uncertainty: 11% for ground state

12 Stability of Event Reconstruction Time variation of 6 Co/ 68 Ge energy Time variation of 1 B/ 1 N event ratio Z dependence of energy deviation Z dependence of vertex deviation

13 Data-set Systematic Uncertainty (DS-1) Mar. 9, - May 1, 7 (pre-purification data-set) (DS-) May 1, 7 - Nov. 4, 9 (post-purification data-set) Detector related no full volume calibration in DS- Reactor related livetime 1486 days 649 days 135 days Fiducial volume 1.8% /.5% νe spectra.4% /.4% Energy scale 1.1% / 1.3% Reactor power.1% /.1% L-selection eff..7% /.8% Fuel composition 1.% / 1.% OD veto.5% /.5% Long-lived nuclei.3% /.4% Cross section.% /.% Time lag.1% /.1%.3% / 3.% 3.3% / 3.4% Total systematic uncertainty (DS-1 / DS-) : 4.1% / 4.5%

14 Reactor Neutrino Status

15 Observed Energy Spectrum:.9 MeV MeV geo neutrinos Efficiency (%) Events/.45MeV exposure : 416 ton-year ( ton-year for KamLAND 8 ) Selection efficiency KamLAND data no-oscillation best-fit osci. accidental C(,n) O best-fit Geo e best-fit osci. + BG + best-fit Geo e E p (MeV) Geo + Reactor combined analysis No osci. expected Background (w/o geo neutrino) Observed events 3-flavor best-fit Geo-neutrinos from U and Th are unconstrained 879 ± ± 6 16 tan +.1 θ 1 = Δm 1= ev sin +.37 θ 13 =.3.37 free parameter : geo neutrinos (U, Th) = (8, 6) events

16 L/E plot P = (observed - B.G.) / (no osci. expected) 1 L : a fixed baseline (18 km) Survival Probability best-fit oscillation Data - BG - Geo e - best-fit oscillation L /E e (km/mev) KamLAND data covers almost cycle of oscillation characteristic of neutrino oscillation

17 KamLAND: 3-flavor oscillation analysis survival probability P 3ν ee = cos 4 θ 13 P ν e'e' + sin 4 θ 13 matter effect electron density N e' N e cos θ 13 atmospheric oscillation length is completely averaged out Δm 31 anti-correlation 13 sin KamLAND+Solar 95% C.L. 99% C.L % C.L. best-fit KamLAND Solar 95% C.L. 99% C.L % C.L. best-fit 95% C.L. 99% C.L % C.L. best-fit +.19 Δm = ev Survival Probability best-fit oscillation Data - BG - Geo e - best-fit oscillation L /E e (km/mev) Best-Fit tan 1 KamLAND only tan θ1 = sin θ13 =.3 (<.94 at 9% C.L.)

18 Oscillation Parameters: - and 3-flavor ) ev -4 (1 1 m (a) -flavor analysis KamLAND+Solar KamLAND 95% C.L. 95% C.L. 99% C.L % C.L. best-fit % C.L % C.L. best-fit Solar 95% C.L. 99% C.L % C.L. best-fit ) ev -4 (1 1 m (b) 3-flavor analysis KamLAND+Solar KamLAND 95% C.L. 95% C.L. 99% C.L % C.L. best fit 99% C.L % C.L. best fit Solar 95% C.L. 99% C.L % C.L. best fit = free tan 1 solar + KamLAND Δm 1 = ev tan θ1 = same result for Δm tan 1 solar + KamLAND Δm 1 = ev tan θ1 = sin θ13 =

19 Geo Neutrino Status (Preliminary)

20 + BG Rate (Events/Day) Reactor e Event rate time variation:.9 MeV -.6 MeV expected event rate (best-fit oscillation, BG estimation, Earth Model) (A) pre-purification expected reactor observed update reactor + non-ν BG + geo-neutrino reactor + non-ν BG preliminary Date Observed Rate (Events/Day) (B) correlation preliminary best-fit reactor + non-ν BG + geo-neutrino reactor + non-ν BG Expected Rate (Events/Day) Constant contribution above the estimated reactor neutrino + non-neutrino background in.9 < E <.6 MeV region Time information is useful to extract the geo neutrino signal

21 Observed Energy Spectrum:.9 MeV -.6 MeV Events /. MeV Efficiency (%) ton-yr data-set (135 days) preliminary KamLAND data E p (MeV) Rate + Shape + Time analysis E p best-fit (U, Th) = (65, 33) Selection efficiency for Geo e Data - BG - best-fit Rea. e Reference Geo e best-fit Reactor e accidental O C(,n) best-fit Geo e best-fit Reactor e + best-fit Geo e estimated fitted + BG w/ solar osci. constraint Rate analysis (.9 < E <.6 MeV) 841 candidates 9 Li. ±.1 Accidental 77.4 ±.1 Fast neutron <.8 (α, n) ± 18. Reactor ν ± 6.5 BG total 79.4 ± excess 111 events 43 Null signal exclusion (rate) 99.55% C.L.

22 Rate + Shape + Time analysis best-fit (U, Th) = (65, 33) U/Th mass ratio fixed Th/U = 3.9 earth model prediction EPSL 58, 147 (7) N Th % C.L. 95.4% C.L. 99.7% C.L. (A) preliminary earth model prediction EPSL 58, 147 (7) 15 1 preliminary (B) 4 model w/o neutrino osc. 3 ratio fixed N U signal is rejected at % C.L. (> 4σ C.L.) N U + N Th +9 Ngeo = 16 8 events Fgeo = /cm /sec +1.3 ( TNU)

23 Radiogenic Heat and Flux s -1 ) - Flux (cm e BSE model (16 TW) crust mantle crust + mantle Kamioka Gran Sasso Hawaii fully radiogenic Radiogenic Heat Production (TW) Fully-radiogenic model KamLAND preliminary Borexino crust mantle Kamioka Gran Sasso Hawaii fully-radiogenic model EPSL 58, 147 (7) crust ( 38 U, 3 Th) 7. TW 4 K, 35 U 3.5 TW mantle ( ) TW uniform mantle mantle bottom only earth model prediction EPSL 58, 147 (7) 38 U, 3 Th 16 TW 4 K, 35 U 3.5 TW Multi-site measurements have just started! Fully-radiogenic model Radiogenic heat production = Surface heat flow (scale U and Th amount in mantle assuming fixed crustal contribution)

24 Test of Fully-Radiogenic Model s -1 ) - Flux (cm e KamLAND preliminary Borexino mantle fully-radiogenic model EPSL 58, 147 (7) crust ( 38 U, 3 Th) 7. TW 4 K, 35 U 3.5 TW mantle ( ) TW uniform mantle mantle bottom only crust Kamioka Gran Sasso v Hawaii earth model prediction EPSL 58, 147 (7) 38 U, 3 Th 16 TW 4 K, 35 U 3.5 TW The observed flux is consistent with the 16 TW model prediction Fully-radiogenic models start to be disfavored KamLAND only.4σ C.L. KamLAND + Borexino.3σ C.L.

25 Future Prospects

26 KamLAND-Zen Experiment KamLAND-Zen test balloon in water R. S. Raghavan PRL (1994) Xenon loaded LS decane 8.3% pseudo-cumene 17.7% PPO.7 g/liter Xenon 3. wt% 4 kg 136 Xe loaded Why use Xe? reactor & geo neutrino measurements continue KamLAND LS dodecane 8% pseudo-cumene % PPO 1.36 g/liter - Isotopic enrichment, purification established - Soluble to LS more than 3 wt%, easily extracted - Slow νββ (T1/ > 1 years) requires modest energy resolution neutrino-less double beta decay search with 136 Xe LS Zero Neutrino Double Beta ν ν νββ 136 Xe

27 KamLAND-Zen Experiment KamLAND-Zen chimney enlargement capability to accommodate CANDLES, CdWO4, NaI and others LS renewal KL LS 8, photon/mev standard LS 1, photon/mev x1.4 > sensitivity (9%C.L.) [mev] <m , kg 136 Xe loaded ~ 5 mev KKDC claim inverted hierarchy Year 17 PMT PMT ~ mev KamLAND ( Xe, 4kg) 136 KamLAND ( Xe, 1kg) 15 SNO+ ( Nd), 56kg 48 CANDLES III ( Ca 3g) 48 CANDLES IV ( Ca 3kg) 1 NEMO-3 ( Mo 7kg) 15 8 SuperNEMO ( Nd or Se 1-) 76 MAJORANA ( Ge), 3-6kg 76 GERDA phasei( Ge:17.66kg) 76 GERDA phaseii( Ge:37.5kg) 76 GERDA phaseiii + MAJORANA( Ge:~8kg) 13 CUORE- ( Te ~1kg) 13 CUORE ( Te 4kg) 136 EXO- ( Xe kg) 136 EXO ( Xe 1t) Winstone Cone photo-coverage > x photon collection > x1.8 target sensitivity ~ mev / 5 years KamLAND-Zen (4 kg 136 Xe) + KamLAND-Zen (1, kg 136 Xe) w/ improved energy resolution useful also for geo neutrino measurement

28 Time Line of KamLAND and KamLAND-Zen item FY Xe enrichment (9%) Mini balloon 14 kg 6 kg 3 kg 3 kg total 14 kg total 4 kg total 7 kg total 1 kg film survey rehearsal production rehearsal production Peripheral R&D installation Others Mirror R&D Physics targets high performance LS R&D 16 event expected (16 TW) 1st phase νβ 4 kg KamLAND upgrade & regal inspection nd phase ~ event expected (16 TW) νβ 1 kg Reactor neutrinos Geo-neutrinos Reactor neutrinos Geo-neutrinos Solar neutrinos

29 Super-KamLAND(-Zen) Experiment Super-KamLAND-Zen Toward further improvement of KamLAND-Zen - Increase the pressure of Xe x4 at 3 m depth - Increase number of photo electrons x3.3 - Reduce 1 C BG by multiple vertex identification 1/1 reduction - Target 136 Xe mass 4 kg 4 tons x1 $M (highest cost) sensitivity ~ 7.6 mev normal hierarchy? 1 ~ 5 mev Super-KamLAND 5 kton LS Another possibility is high statistics LS detector geo neutrino ~ 1 events / 5 kton / yr flux at < 1% accuracy but... effect from local geology ~ 1% s -1 ) - Flux (cm e 1 1 KamLAND preliminary Borexino mantle precise subtraction of the crustal contribution is more important crust Kamioka Gran Sasso Hawaii

30 data-set : 881 ton-yr 416 ton-yr Summary Anti-neutrino results in KamLAND are improved. improved radio-purify by LS purification Geo-neutrino (preliminary result) reactor power reduction (α, n) B.G. reduction ~ 1 / Reactor-neutrino (available at hep-ex/ ) - Three-flavor oscillation analysis is presented solar + KamLAND Δm +.19 tan θ1 = = ev (3-flavor) sin θ13 = Observed flux is fully consistent with Earth model - Fully-radiogenic model starts to be disfavored Observed geo-neutrino event flux events /cm /sec (mass Th/U = 3.9)

31 Multi-site measurements have just started! Multi-site measurements and/or a measurement on the oceanic crust (e.g. Hawaii) will be important to advance neutrino geophysics. Future Prospects KamLAND-Zen starts in 11 with 4 kg 136 Xe, aiming at the effective mass ~ 5 mev. KamLAND, KamLAND-Zen,... experiments will continue to measure the geo neutrino flux including future detector improvements.