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Geoneutrino Overview

Geoneutrino Overview. 1 ． Review of Geoneutrino Physics (with KamLAND) 2 ． KamLAND Result and Prospects 3 ． Physics with Proposed Detectors. Sanshiro Enomoto KamLAND Collaboration RCNS, Tohoku University.

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Geoneutrino Overview

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  1. Geoneutrino Overview 1．Review of Geoneutrino Physics (with KamLAND) 2．KamLAND Result and Prospects 3．Physics with Proposed Detectors Sanshiro Enomoto KamLAND Collaboration RCNS, Tohoku University Neutrino Science 2007 – Deep Ocean Anti-Neutrino Observatory Workshop, Univ. of Hawaii at Manoa, March 23-25 2007

  2. Geoneutrinos • Geoneutrinos are produced by • Direct measurement of HPE • U:~8TW, Th: ~8TW, K: ~3TW • Geoneutrinos are detected by • Two consecutive signals • Threshold 1.8 MeV • Not sensitive to 40K;other targets discussed [M.C.Chen (2005)] Threshold: 1.8 MeV

  3. KamLAND: The First Detector Sensitive to Geoneutrinos Detector Center Liquid Scintillator 1000 tonContained in plastic balloon Surrounded by 17-inch PMT1325 20-inch 554 (PMT : Photo Multiplier Tube, a photo sensor) Liquid Scintillator 20m • Yields light on ionization (8000 photons / MeV) • Mainly consists of only C and H

  4. KamLAND Location Geological Setting • Boundary of Continent and Ocean • Island Arc (Orogenic) • ‘Hida’ Metamorphic Zone • Zn, Pb, limestone mine (skarn) • Surrounded by Gneiss Rocks KamLAND You are here Sea of Japan KamLAND JapanTrench KamLAND is surrounded bya number of nuclear reactors

  5. First Result from KamLAND [T. Araki et al. (2005)] • Fiducial Volume: 408 ton • Live-time: 749 days • Efficiency: 68.7% • Expected Geoneutrinos • U-Series： 14.9 • Th-Series：4.0Backgrounds • Reactor： 82.3±7.2 • (α,n) ： 42.4±11.1 • Accidental：2.38±0.01BG total： 127.4±13.3 • Observed： 152 Number of Geoneutrinos: 25 ＋19 －18

  6. A Reference Earth Model to Predict Flux • BSE composition by [McDonough1999] • Crustal composition by [Rudnick et al. 1995] • Crustal thickness by CRUST 2.0 • Uniform Mantle Model • No U/Th in the Core • Expected Geoneutrino Flux • U-Series • 2.3x106 [1/cm2/sec] • Th-Series • 2.0x106 [1/cm2/sec] Geoneutrino Origination PointsDetectable at KamLAND (MC) 50% within 500km25% from Mantle KamLAND • With 1032 target protons, • U-Series • 32 events / year • Th-Series • ８ events / year Australia Greenland Total 19 is predictedfor KamLAND 749 days Antarctic South America

  7. Uncertainties of the Model • Geochemical / Geophysical datararely come with error estimation • Fiorentini et al. (2005) • Error is given as “spread in published estimates” • Fogli et al. (2006): GeoNeutrino Source Model (GNSM) • Correlations (reservoirs, elements) added • Enomoto et al. (2005) • Inversion framework discussed

  8. Local Geological Effects • ~50% of flux comes within ~500km radius • ~25% within ~50km • Characteristic U/Th depletion in Japan Arc[Togashi et al. (2000)] • U: -17%, Th: 22% ⇒ affects total flux at 6.4% (U) and 8.4% (Th) • Surface heterogeneity[Enomoto et al. (2005)] • 20% flux variation possible ⇒ 3.2% uncertainty in total flux • Vertical heterogeneity ??? ~500km

  9. Other Source of Uncertainties • Crustal Thickness Map Resolution (2×2 deg) • 3~4% Total Flux Uncertainty • Neutrino Oscillation Parameter (sin22θ=0.82±0.07) • 6% Flux Uncertainty Comparison of CRUST 2.0 and Zhao et al. CRUST2.0 Propagation of crustal thickness error Zhao et al. (1992)

  10. Summary of Total Flux Uncertainties • Global Modeling (not uncertainty; our interest) • BSE comopsition: ~20% • Mantle models (uniform / layered): <3% • Local Geological Effects • Island Arc Characteristics: 6-8% • Surface Geology Heterogeneity: 3.2% • Vertical Heterogeneity: ??? • Other Uncertainties • Crustal Thickness Map Resolution: 3~4% • Neutrino Oscillation Parameter: 6%

  11. Flux Prediction from Earth Models Scale Bulk Composition Geoneutrino Flux [1/cm2/sec] Fix Crustal Composition, Parameterize Mantle U+Th Mass[kg]

  12. KamLAND Result [T. Araki et al. (2005)] • Fiducial Volume: 408 ton • Live-time: 749 days • Efficiency: 68.7% • Expected Geoneutrinos • U-Series： 14.9 • Th-Series：4.0Backgrounds • Reactor： 82.3±7.2 • (α,n) ： 42.4±11.1 • Accidental：2.38±0.01BG total： 127.4±13.3 • Observed： 152 Number of Geoneutrinos: 25 ＋19 －18

  13. KamLAND Spectrum Analysis Parameters NU, NTh: Number of Geoneutrinos sin22θ, Δm2 : Neutrino Oscillation α1, α2: Backgrounds Uncertainties Total Number of U and Th • KamLAND is insensitive to U/Th ratio→ adopt U/Th ~ 3.9from Earth science • Number of Geoneutrinos：28.0 • 99% C.L. upper limit：70.7 events • Significance 95.3% (1.99-sigmas) ＋15.6 －14.6 Discrimination of U and Th

  14. Comparison with Earth Model Predictions KamLAND 99% Limit Geoneutrino Flux [1/cm2/sec] KamLAND 1-σ Range Earth Model Prediction U+Th Mass[kg] • Consistent with BSE model predictions • 99%C.L. upper limit too large to be converted to heat production (No Earth models applicable)

  15. KamLAND Problem (α,n) BG Reactor Neutrino BG 210Pb 222Rn 22.3 y 3.8 d n + p → n + p 13C (α,n) 16O 210Bi 210Po 206Pb Cross-section error: 20% 5.013 d 138.4 d stable Quenting factor error: 10% 210Po decay rate error 14%

  16. New (α,n) Cross section data available Vertex reconstruction algorithm improved Proton quenching factor measurement 210Po-C source calibration performed⇒ (α,n) error reduced from ~26% to ~5% KamLAND Prospects (1) (α,n) Background error had been reduced P quenching measurement Po-C Calibration (MC/Data)

  17. KamLAND Prospects (2) LS Distillation in Progress⇒ removes radioactivity by 10-5 we remove these BEFORE AFTER Another 749 days operation after purification, • Error is reduced：from 54% to 28% (error is dominated by reactor neutrinos) • Significance： 99.96%

  18. KamLAND Prospects Upper limit (~40TW)comparable withheat flow(~40TW) 28% uncertainty

  19. Future Geoneutrino Experiments

  20. The World Map of Geoneutrino Flux Typical Rate from Crust 30~70 /1032P/year from Mantle ~10 /1032P/year

  21. Reactor Neutrino Backgrounds KamLAND-II 750 days （expected） without reactor BG

  22. The World Map of Geoneutrino S/N Ratio

  23. Geoneutrino Flux @ Future Detector Sites KamLAND SNO+ Hanohano Borexino LENA

  24. Required Exposure for 20% precision determination Typical Time on CC, estimate BSE 0.5~1 [1032P・year] on CC, estimate M ~30[1032P・year] on OC, estimate M 4.5 [1032P・year] Sensitive to Crustal Composition Sensitive to Mantle Composition Worst Place

  25. Sensitivity to “Regional” Structure Gran Sasso / Mesozoic Crust Kamioka / Island Arc Hawaii / Oceanic Island Sudbury / Archean Crust • We have to discriminate the global and regional signature • Correlation matrix used by GNSM (Fogli et al (2006)) could be extended ?? • if correlation coefficients among different crustal types are given.

  26. Plumes, Ocean Ridges, … Neutrino Detector on Plume At Tahiti, 13% comes from “hot” mantle⇒ sensitive to a factor enrichment Neutrino Detector on Mid-Ocean Ridge If the mantle beneath mid-ocean ridge Is depleted by a factor, it should be visible Portable detector (like Hanohano)will open new application

  27. Summary • Geoneutrino provides a direct measurement of heat producing elements (HPE) • KamLAND measurement will be improved • Reduced systematic error for existing data • Radioactive BG reduction by LS distillation • Multiple site measurement is important • Reduction of local geological effects • Separation of mantle and core • Sensitivity to regional characteristics • No nuclear reactor BG • Wish List • Error estimations for U/Th content in each reservoir • Better resolution crustal map

  28. Backup Slides Appendix

  29. Geoneutrino Spectrum

  30. Geoneutrino Angular Distribution at Kamioka

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