Status of Reactor Neutrino Oscillation and Geo Neutrino Measurement in KamLAND

Transcription

1 Status of Reactor Neutrino Oscillation and Geo Neutrino Measurement in KamLAND The 3rd GCOE International Symposium Feb. 17, 11 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 Kamioka Liquid Scintillator Anti-Neutrino Detector neutrino ニュートリノ cosmic-ray 宇宙線 operated since Kamioka Mine 13 m 1, m depth 1, ton Liquid Scintillator Dodecane (8%) Pseudocumene (%) PPO (1.5 g/l) 1,35 17 inch inch PMTs commissioned in February, 3 photocathode coverage : % 34% 18 m Water Cherenkov Outer Detector

4 Reactor Neutrino Oscillation

5 MNS (Maki-Nakagawa-Sakata) Matrix V = ν e ν µ ν τ = V e1 V e V e 3 V µ1 V µ V µ 3 V τ1 V τ V τ 3 Δm 3 Δm 1 θ 3 θ 13, CP phase θ 1 1 c 3 s 3 s 3 c 3 atmospheric Neutrino Oscillation ν 1 ν ν 3 c 13 s 13 e iδ s 13 c 13 m ν 3 6 parameters : 3 mixing angle, mass difference, 1 CP phase ν ν 1 c 1 s 1 s 1 c 1 1 solar normal atmospheric solar Majorana phase e iρ e iσ 1 m inverted ν solar ν 1 atmospheric ν 3 + Majorana phase Investigated by neutrino oscillation experiments future subject : determination of θ 13 and CP phase

6 Reactor Neutrino Oscillation L Inner tank ν e ν e 1, ton LS Outer water tank Kamioka effective L ~ 18 km P(νe νe) P( e --> e ) sin θ1 =.9, sin sin 13 =.1 θ13 assumed =.1 assumed Normal Hierarchy Inverted Hierarchy KamLAND L L(km) (km) flavor neutrino oscillation 1.7 m P (ν e ν e )=1 sin θ 1 sin 1 [ev ]L[m] E[MeV] 3 flavor neutrino oscillation 1.7 m P (ν e ν e ) cos 4 θ 13 1 sin θ 1 sin 1 [ev ]L[m] E[MeV] F. ERICE9 + sin 4 θ 13

7 Anti-Neutrino Detection inverse beta-decay reaction γ e + ν e p prompt γ n mean n-capture time on proton ~ 7 µsec delayed. MeV Tight background rejection by delayed coincidence γ (a) accidental B.G. discrimination.5 < ΔT < 1 µs ΔR < m 1.8 MeV < E delayed <.6 MeV or 4. MeV < E delayed < 5.8 MeV.9 MeV < E prompt < 8.5 MeV R prompt, R delayed < 6. m L-selection from 6 parameters (b) µ spallation cut ΔTµ > s after showing µ ΔTµ > s or ΔL > 3 m after non-showering µ (ΔQ < 1 6 p.e.)

8 Dominant Background : (α, n) Reaction 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 kev(nd excited state) kev(1st excited state) + + prompt γ (6.1MeV) or e + e - (6.MeV) recoil proton 16 p O delayed n γ (.MeV) 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

9 Background Summary backgrounds from cosmic-ray muons backgrounds from radioactive impurity without geo neutrinos Oscillation analysis (Rate + Shape + Time) reduced by LS purification! geo neutrinos Time evolution of reactor neutrinos and backgrounds is incorporated in the likelihood term free parameter (no time evolution)

10 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

11 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 strong evidence of neutrino oscillation

12 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.)

13 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 =

14 global analysis: solar + KamLAND + CHOOZ + Atmospheric + LBL significance of nonzero θ13 79% C.L. sin θ13 = Global Analysis % C.L. 95% C.L. 9% C.L. Global CHOOZ + Atmospheric + LBL KamLAND + Solar Solar KamLAND sin M. Gonzalez-Garcia et al. hep-ph/11.454v3 Global analysis: significance of nonzero θ 13 is at 79% C.L. 13 This work

15 Oscillation Parameters Results from 3 flavor oscillation analysis Δm 1 is determined with.7% precision from KamLAND θ1 and θ13 are measured from global analysis hint of nonzero θ13? More definitive information on the value of θ 13 will come from accelerator and reactor experiments in the near future 3

16 Geo Neutrino Measurement

17 Geophysical Activity formation of mountains geomagnetic reversal volcano Question on geophysical activity mantle convection plate motion earthquake What are energy sources How much energy? How is the mantle convecting, single or multi-layer convection? Why is the frequency of geomagnetic reversals random

18 Neutrino from the Earth Heat sources in the Earth (1) Radiogenic heat from U, Th, K decay () Release of gravitational energy through accretion or metallic core separation (3) Latent heat from the growth of inner core U series Th series anti-neutrinos from beta-decay Radiogenic heat : α-decay or β-decay emitting anti-neutrinos

19 Heat Balance Surface heat flow 44TW > Radiogenic heat 19 TW Bulk Silicate Earth (BSE) model chondrite meteorite U : 8 TW Th : 8 TW K : 3 TW Almost half of radiogenic heat contributes to the surface heat flow secular cooling Heat source at the core Geomagnetic field is generated by convection in the fluid outer core heat source for the convection latent heat or release of gravitational energy or radiogenic heat? Geo neutrino directly tests radiogenic heat generation

20 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) 4 K Window for KamLAND 38 U 6 Pb 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 MeV(1.7%)

21 + 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

22 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 ± 3.3 excess events Null signal exclusion (rate) 99.55% C.L.

23 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 N U + N Th signal is rejected at % C.L. (> 4σ C.L.) Ngeo = 16 Fgeo = events 1 6 /cm /sec +1.3 ( TNU)

24 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! The observed flux is consistent with the 16 TW model prediction Fully-radiogenic models are disfavored KamLAND only.4σ C.L. KamLAND + Borexino.3σ C.L.

25 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) - Observed flux is fully consistent with Earth model - Fully-radiogenic models are disfavored 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 geo-neutrino event events flux /cm /sec (mass Th/U = 3.9)

26 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 experiment starts in 11, to search for neutrino-less double beta decay see Shirai s talk We will continue the anti-neutrino measurements also in KamLAND-Zen phase for further improvement