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Geo-neutrino: Experiments

Geo-neutrino: Experiments. BNO. Jelena Maricic Drexel University Neutrino Champagne – LowNu2009 October 20, 2009. Outline. Geological motivation for geo-neutrinos Experimental detection of geo-neutrinos and search for geo-reactor with KamLAND detector

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Geo-neutrino: Experiments

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  1. Geo-neutrino: Experiments BNO Jelena Maricic Drexel University Neutrino Champagne – LowNu2009 October 20, 2009

  2. Outline • Geological motivation for geo-neutrinos • Experimental detection of geo-neutrinos and search for geo-reactor with KamLAND detector • Prospects for precision measurement of geo-neutrino flux and geo-reactor discovery with current and planned experiments • Further developments of detection techniques • Summary J. Maricic, Drexel University

  3. Geologists agree! We know more about the Sun than about Earth under our feet Geological motivation for geo-neutrinos J. Maricic, Drexel University

  4. What and How We Learn About Earth Interior? • Chemical composition: • Depth up to 670 km studied directly: melts or • drilling (12km). • Deep Earth inaccessible. Guess composition by • abundances in meteorites and sun. • (670-6400km) • Density profile: • Sound velocities from seismic data • Total mass and moments: infer density profile • Does not resolve chemical composition! • Geodynamics: • Continental drift energized by internal heat flow • Geomagnetic field attributed to the dynamo • effect of the core • Energy source that powers the dynamo not • understood! • Heat flow: • 43-49 TW. Not well constrained due to model • dependence (maybe 30-32 TW ?!?) • 17-23 TW are from radioactivity in • 40K, 232Th, 238U (trace elements); • predominant heat source J. Maricic, Drexel University

  5. Where are Radioactive Elements Located? • Based on the Earth’s chemical composition model: • U/Th expected mostly in the crust and mantle • More U/Th expected in the crust than mantle • No U/Th expected in the core, but deep Earth is highly • inaccessible. If it is there, does it burn, breed? •  deep-core fission reactor proposed by M. Herndon as • energy source driving geodynamo – radical hypothesis • K seems to be under-abundant on Earth: • Some models suggest that it is accumulated in the core Deep core fission reactor? U, Th, K? J. Maricic, Drexel University

  6. Direct Measurement of U/Th Content with Geoneutrinos • Antineutrinos (geo-neutrinos) are emitted in the decay chains of • 40K, 232Th, 238U • - Low energy < 3.4 MeV; 232Th neutrinos have lower end point than 238U neutrinos • - Can engage in inverse β-decay • reaction • - Only U and Th geo-neutrinos • can be detected this way • From the measurement of geo-neutrino flux, • inferences about U/Th • content of the entire • Earth can be made! Inv.  reaction: e p+  e+ + n Only good for detection of neutrinos with energies > 1.8 MeV. Inv.  does not work for 40K! J. Maricic, Drexel University

  7. Geo-neutrinos vs. Conventional Geological Toolsin Surveying Earth Interior? Conventional geology uses indirect methods to learn about the Earth’s composition: - replicated in the laboratory - only the very outside surface layers can be directly sampled - a lot of educated guessing must be invoked to fill in gaps in the story of Earth’s evolution - meteorite data Geo-neutrinos provide a direct method – instantaneous information about full radioactive heat production from 232Th and 238U from ENTIRE Earth. - 232Th and 238U fluxes provide evidence about the amounts and distribution (crust, mantle, or even core) of 238U and 232Th - unique input in geochemistry and geodynamics. Existence of geo-reactor neutrinos would provide direct evidence about geo-reactor existence and viable explanation for the energy source of the geomagnetic field + radical change in planetary chemistry and evolution. • Geo-neutrinos  direct evidence for understanding: • - Earth energy budget (heat flow) • - Plate tectonics (driving mechanism) • - Energy source of geodynamo (geomagnetism) • - Chemical composition • - Planet formation J. Maricic, Drexel University

  8. How even crude measurement is very exciting Experimental Detection of geo-neutrinos and search for geo-reactor with Kamland experiment J. Maricic, Drexel University

  9. Geoneutrinos Reactor Background with oscillation KamLAND: reactor vs. geo-neutrinos • KamLAND – 1 kton scintillator detector • Detects electron anti-neutrinos via inverse beta decay Prompt Event γ γ e+ p γ νe p n 2.2MeV 200 μs Delayed Event J. Maricic, Drexel University

  10. Crust vs. Mantle Geo-Neutrinos at KamLAND S. Enomoto • Crust thickness: • - continental ~40 km • oceanic ~8 km • U, Th are lithophile: • strong tendency to • leave the mantle and • stay in the crust • U, Th more abundant • in the crust • Sensitivity to mantle • neutrinos small, • due to the vicinity of • continental crust KamLAND Sea of Japan Geological Setting KamLAND • Boundary of Continent and Ocean • Island Arc • Zn, Pb, limestone mine (skarn) JapanTrench J. Maricic, Drexel University S. Enomoto

  11. Local vs. Global Neutrinos at KamLAND Assuming uniform crustal composition(no local variation)! 50% of flux within 500 km from KL. Geoneutrinos from the crust dominant! KamLAND is looking at‘Earth around Japan’,if local variation is averaged enough S. Enomoto ‘Earth around Japan’ Japan Island Arc Hida Metamorphic Zone Kamioka Mine J. Maricic, Drexel University

  12. Expected Neutrino Spectrum at KamLAND Antineutrinos coming from nuclear reactors around Japan present the largest source of bkg in KamLAND. Geo-neutrino analysis window U/Th flux small comparing to reactor flux and bkgs. Reactor neutrino analysis window Geoneutrinos + BG Poor signal to bkg ratio! Total BG Expected event rate: U series: 14.9 Th series: 4.0 Reactor (E<3.4MeV): 80.4 Reactor (,n) Accidental *749.14 days of livetime J. Maricic, Drexel University

  13. Analysis Results (749.14 days livetime) Unbinned spectrum-shape Maximum Likelihood method used for analysis. Confirmation 101 years after Rutherford proposed radioactivity as the source of Earth’s heat Best fit point Incorporates Th/U = 3.9 constraint Good Agreement Comparison of energy spectrum of observed events with expectation. Geophysical model +19 - 18 Observed: (25 ) events • 90% confidence interval: 4.5 to 54.2 • 99% C.L. upper limit：70.7 • Ngeo=0 excluded at 95.3%(1.99σ) J. Maricic, Drexel University

  14. KamLANDResults (2008) Model Data Fit • - Enlarged fiducial volume (6 m vs. 4.5 m) • - Livetime: 1491 days • - Analysis threshold: 0.9 MeV • - Geonu flux from Enomotoet al. • model: 16TW U+Th total • U&Th strongly anti-correlated J. Maricic, Drexel University

  15. Search for Geo-reactor Neutrino Signal at KamLAND • Reactor anti neutrinos only - above 3.4 MeV • The possible surplus of detected events implies that there may be another source of antineutrinos that has not been accounted for  geo-reactor. • With 2.5 times more data, statistics improved: 90% 68% First results New results The best fit value (04) TW and 90% C.L. limit 6.2 TW with 1491 days of livetime (2008) The best fit value (66) TW and 90% C.L. limit 19 TW with 515 days of livetime (2005) J. Maricic, Drexel University

  16. KamLAND Prospects • Next result – improved geo-neutrino and geo-reactor measurement (prospects – exclude 0 geo-neutrino hypothesis and fully radiogenic heat hypothesis > 3) • Precision measurement unlikely – can not constrain/differentiate among different geological models • No discovery level geo-reactor neutrino measurement (5 level) • Low sensitivity to geo-neutrinos from the mantle (in high demand by geologists) Scintillator purification decreased it - 1/10 or better Reactor flux ~50% in last 2 years J. Maricic, Drexel University

  17. BNO What it takes for precision measurement Prospects with other running and planned neutrino experiments J. Maricic, Drexel University

  18. Locations for Possible Geonu Experiments SNO+ (soon – 1 kton) 5400 mwe LENA(R&D – 50 kton) Baksan(R&D) DUSEL (R&D – 300 kton) 4200 mwe Hanohano (R&D – 10 kton) 4000 mwe KamLAND (running – 1kton) 2700 mwe EARTH (R&D) (Fiorentini et al JHEP2004) Borexino (running – 300 ton, 3700 mwe) Color indicates U/Th neutrino flux, mostly from crust

  19. Geonu Crust and Mantle Signal at Various Detector Sites S. Enomoto M. Chen Hanohano Hawaii KamLAND Japan KamLAND Canada Hanohano • Geoneutrino flux determination – synergy among experiments: • Continental (KamLAND, SNO+, • Borexino, LBNE at DUSEL, LENA, …)  geo-neutrino flux from the crust – multiple • sites crucial for reliable Earth model • Oceanic (Hanohano)  geoneutrino flux from the mantle

  20. Reactor Neutrino Backgrounds Geoneutrinos Reactor Background with oscillation Commercial nuclear reactor background KamLAND Japan KamLAND Hawaii Hanohano

  21. Borexino experiment • 300 ton liquid scintillator detector • (running from 2007) • Mostly sensitive to geo-neutrinos • from the crust • Comparable signal from crust and reactors (Fiorentini et al JHEP2004) • 5-7 geo-neutrinos/year; 2 years for 3 • (Borexino collaboration - European Physical Journal C 47 21 (2006) - arXiv:hep-ex/0602027) • Geo-reactor signal: 5-21% of reactor • signal (1-6 TW) J. Maricic, Drexel University

  22. SNO+ experiment • 1 kton liquid scintillator detector (will start 2011) • Mostly sensitive to geo-neutrinos from the crust • Comparable signal from the crust and reactors • 28-38 events/year (Chen, M. C., 2006, Earth Moon Planets 99, 221) • Should measure U/Th ratio of the crust • Geo-reactor signal: 2.7 – 16% of reactor signal (1-6 TW) J. Maricic, Drexel University

  23. Hanohano • 10 kton liquid scintillator detector (R&D) • Very sensitive to mantle neutrinos • 60 – 100 events/year (J. G. Learned et al. – ``XII-th International Workshop on Neutrino Telescope'', Venice, 2007) • Should measure mantle U/Th • 1:1 geo-reactor and man-made reactor signal ratio • Almost 5 C.L. even for 1 TW gr. J. Maricic, Drexel University

  24. LENA • 50 kton liquid scintillator detector (R&D) • Mostly sensitive to crust neutrinos • Geo-neutrino signal dominates over reactor signal • Should measure U/Th ratio in the crust • 800-1200 events/year (K. A. Hochmuth et al. - Astropart.Phys. 27 (2007) – arXiv:hep-ph/0509136) • LS loaded with 0.1% Gd • Geo-reactor signal: 6.2 – 37.5% of reactor signal (1 – 6 TW) J. Maricic, Drexel University

  25. LBNE at DUSEL • 300 kton detector (WCh maybe loaded with Gd or LS) • If filled with LS – very sensitive to geo-neutrinos from the crust • Should obtain U/Th in crust • 4800 – 7200 events/year (scaled from LENA) • Sensitive to geo-reactor even in the case of Gd loading (4.5 MeV threshold vs. 3.4 MeV) • Geo-reactor signal: 15 – 92.3 % of reactor signal (1-6 TW) J. Maricic, Drexel University

  26. What geologists would really like to know Potassium 40 J. Maricic, Drexel University

  27. Measuring Potassium 40 Content • Radiogenic heat from potassium 40 estimated at 3 TW • Potassium 40 below inverse beta decay threshold • Neutrino flux overwhelmed by solar neutrinos by 2-3 orders of magnitude • Other low Qb and low ft elements searched like 106Cd(see M. Chen, Neutrino Sciences 2005) and many others (Kobayashi et al, Geophys. Res. Lett 18(633) 1991 J. Maricic, Drexel University

  28. Uncovering neutrino detection in scintillation detectors Improving detection technique with directionality J. Maricic, Drexel University

  29. Directionality of neutrino in inverse beta decay • Neutron remembers the direction – useful for geo-neutrino detection • Rejection of reactor backgrounds • Problems: blurred due to thermalization, poor reconstruction and gamma diffusion • Improvement: element with large neutron c-s; heavy particle emission; good vertex resolution • Li under study at Tohoky University • Transparency • 45% of KL light yield • 7.59% natural abundance - possible enrichement Prompt Event γ γ e+ p γ νe p n 2.2MeV 200 μs Delayed Event J. Maricic, Drexel University S. Enomoto

  30. J. Maricic, Drexel University

  31.  Summary • Geo-neutrinos provide direct measurement of radioactive elements and heat produced • Geo-neutrinos are the only chemical probes of entire planet • KamLAND measured geo-neutrinos at 2  and 4  expected in 2 years • Limit on geo-reactor set by KamLAND at 6.2 TW (90% C.L.) –range of interest for core • Borexino is operational, while SNO+ soon • Future hopes – detectors in the ocean, very large LS detectors, several locations, directionality , K40…   J. Maricic, Drexel University

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