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Probing the Earth's Interior with Neutrinos

Probing the Earth's Interior with Neutrinos. John Learned University of Hawaii at Manoa With thanks to Jelena Maricic, Steve Dye, KamLAND colleagues and others for slides. AGU Meeting Baltimore 10 May 2006. Outline. Whazza neutrino? Where they come from? How detect?

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Probing the Earth's Interior with Neutrinos

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  1. Probing the Earth's Interior with Neutrinos John Learned University of Hawaii at Manoa With thanks to Jelena Maricic, Steve Dye, KamLAND colleagues and others for slides AGU Meeting Baltimore 10 May 2006

  2. Outline • Whazza neutrino? Where they come from? How detect? • Why do geophysicists care? • Experimental detection of geo-neutrinos and search for geo-reactor with various existing and proposed detectors • Summary and conclusion.. fun with new initiatives. AGU Meeting Baltimore

  3. unstable u up c charm t top Atom Proton Quarks d down s strange b bottom Quarks Electrons Nucleus e electron μ muon τ tauon Neutron Leptons νe electron neutrino νμ muon neutrino ντ tau neutrino 3 Kinds of Neutrinos - Fundamental constituents of universe, 3 of 6. - Maybe most numerous particle. - As much mass as all the stars. - Pass through earth easily. - Weird property of changing types in flight. - Much ferment in field in last decade! The Fermions AGU Meeting Baltimore

  4. Nuclear Reactors (power stations, ships) and Nuclear Weapons  Sun  Particle Accelerator  Supernovae (star collapse) SN 1987A  Earth’s Atmosphere (Cosmic Rays)  Astrophysical Accelerators Soon ? Earth’s Crust (Natural Radioactivity) Big Bang (here 330 /cm3) Indirect Evidence Where do Neutrinos come from? AGU Meeting Baltimore 

  5. Prompt Event Cherenkov radiation ≈ 20µs Delayed Event n + Gd  Gd + g cascade Evis ≈ 3~8 MeV Detecting Electron Antineutrinosold Reines mechanism Inverse Beta Decay AGU Meeting Baltimore 2 flashes close in space and time Rejects most backgrounds

  6. What do we Know about the deep Earth? • Chemical composition: • Depth up to 670 km studied directly: melts or drilling (12km). • Deep earth inaccessible. Guess composition by abundances in meteorites and sun. • 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: • 30 – 45 TW. Not well constrained due to model dependence • 19 – 31 TW are from radioactivity in 40K, 232Th, 238U (trace elements); predominant over other heat sources AGU Meeting Baltimore We need direct probes…. Neutrinos!

  7. Where are Radioactive Elements Located? • Based on the Earth’s chemical composition model: • U/Th expected mostly in the crust and mantle • No U/Th expected in the core, but deep Earth is highly inaccessible. If it is there, does it burn, breed? • K seems to be under-abundant on Earth: • Some models suggest that it is accumulated in the core • Better constraints on the amounts and distribution of the radioactive elements throughout the Earth crucial for understanding of: • heat flow, geomagnetism, plate tectonics • chemical composition and planet formation AGU Meeting Baltimore

  8. 234U 238U 234Pa 230Th 234Th 228Th 232Th 40Ca 228Ac 40K 226Ra 224Ra 228Ra 40Ar 222Rn 220Rn 218At 210Po 214Po 218Po 212Po 216Po 210Bi 214Bi 212Bi 206Pb 210Pb 214Pb 208Pb 212Pb 210Tl 208Tl Radiogenic Isotopes Produce Neutrinos • Beta decays produce electron antineutrinos AGU Meeting Baltimore

  9. Expected Neutrino Spectrum at KamLAND, example • 408ton CH2 (5m radius volume), 749.14 days, 69% efficiency • Oscillation parameters from KamLAND 2nd Result geoneutrino analysis window reactor neutrino analysis window AGU Meeting Baltimore Geonu expected event rate: U series: 14.9 Th series: 4.0 Reactor (E<3.4MeV): 80.4

  10. Locations for Geonu Experiments SNO+ LENA Baksan Homestake Hanohano Kamland AGU Meeting Baltimore EARTH Borexino Color indicates U/Th neutrino flux; red-green: mostly from crust; blue: mostly mantle/core

  11. Compare Geonu Detectors AGU Meeting Baltimore 10.0 90 30 45 These may be first steps in worldwide reactor monitoring network.

  12. Mantle Geo-neutrinos are Scarce (1032 proton-yrs = 1 TNU ≈ 1.2 kT-y of KamLAND oil) • Predicted geo-neutrino signal at different world location, based on the traditional Earth model • In the oceans, far from continents, signal dominated by mantle geo-neutrinos (oceanic crust is very thin: 5km compared to 30km on continents • U/Th concentration in mantle thought to be very small. AGU Meeting Baltimore

  13. Japan: ~1:3 Hawaii: ~3:1 What is Important for Mantle Geo-neutrino Measurement? Keep backgrounds small! Location! Signal Backgrounds AGU Meeting Baltimore + geo-reactor }mantle : crust ~ 8 events/Kt•year expected from mantle

  14. Long Range Future:Other Neutrino Geophysics Possibilities • Earth tomography using neutrino factories plus giant detectors. • Maybe also with natural high energy neutrinos. • Potential to search for oil, measure earth inhomogeneities, directly measure core properties AGU Meeting Baltimore

  15.  Summary and Conclusion • Interest in geo-neutrinos have risen dramatically over the last year. • First ever detection of geo-neutrinos • First ever upper limit on the power of geo-reactor • Promising future for precision measurements that will reveal secrets of the Earth’s interior. • Moving toward larger and larger detectors, makes neutrinos viable for applications. • Physics prospects will mega-ton size detectors also amazing: geo-neutrino tomography, supernova neutrino detection, nucleon decay search, exotic particles searches, ... • We look to an interesting multi-disciplinary future! AGU Meeting Baltimore   Join the Fun!

  16. AGU Meeting Baltimore

  17. Introduction

  18. Convection in the Earth AGU Meeting Baltimore • The mantle convects even though it is solid. • It is responsible for the plate tectonics and earthquakes. • Oceanic crust is being renewed at mid-ocean ridges and recycled at trenches. Image: http://www.dstu.univ-montp2.fr/PERSO/bokelmann/convection.gif

  19. Overview of Earth Heat AGU Meeting Baltimore *Abundances from John Verhoogen, 1973

  20. Total Heat Flow from the Earth Bore-hole Measurements • Conductive heat flow measured from bore-hole temperature gradient and conductivity • Deepest bore-hole (12km) is only ~1/500 of the Earth’s radius. • Total heat flow 44.21.0TW (87mW/m2), or 311TW (61mW/m2) according to more recent evaluation of same data despite the small quoted errors. AGU Meeting Baltimore Image: Pollack et. al

  21. KamLAND: Detector Design 1000ton 225 20-inch 13m diameter AGU Meeting Baltimore LS: 13m 80%: dodecane20%: pseudocumene1.5g/l: PPO 1.75m thickness 1325 17-inch 554 20-inch ~ 8000 photons/MeV λ~ 10m MO: 20m 50%: dodecane50%: isoparafin photo-coverage: 34% ~ 500 p.e. / MeV ρLS/ρMO = 1.0004

  22. KamLAND Experiment • Observes low energy anti-neutrinos. • Located in Japan. • Placed in the mine, under mountain Ikenoyama, 1000 meters underground. • Consists of 1000 ton scintillator detector surrounded by 1845 PMTs. • Reaction: 1km 20m AGU Meeting Baltimore

  23. Where KL Geo-neutrinos Come From? Assuming uniform crustal composition(no local variation), KamLAND Australia Greenland AGU Meeting Baltimore Antarctica South America ‘Earth around Japan’ Japan Island Arc KamLAND is looking at‘Earth around Japan’,if local variation is averaged enough Hida Metamorphic Zone Kamioka Mine

  24. Geo-neutrino Detection Summary +19 - 18 • KamLAND result: (25 ) - in agreement with Earth model predictions (19 geo-neutrinos). • The first ever detection of geological neutrinos. • Zero geo-neutrino hypothesis excluded at almost 2σ • However, KamLAND result: • Does not constrain models  precision measurement needed! • Predominantly sensitive to geo-neutrinos from the crust  • mantle geo-neutrinos measurement needed (make geologists very happy!) AGU Meeting Baltimore

  25. Geo-reactor Search Analysis Summary • Upper limit on the power of the geo-reactor have been set for the first time. • The best fit is: • Upper limit on geo-reactor power is 19 TW at 90% C.L. • Final result greatly influenced by the input oscillation parameters. • KamLAND size detector far away from nuclear reactors needed for high confidence (>99.99%) measurement. • Hawaii presents an excellent choice for a definite geo-reactor measurement (Hanohano). PRELIMINARY AGU Meeting Baltimore

  26. Hawaiian Anti-Neutrino ObservatoryHanohano • 10 kiloton “KamLAND in the ocean” type of detector • Portable design, construct and test at pier. • Physics objectives: • 15% measurement of mantle geo-neutrinos (U/Th) – (81) TW (haven’t been measured so far) • Search for > 1 TW geo-reactor • Neutrino applications objective: • Benchmark study for the potential future neutrino detector array designed for remote monitoring of nuclear reactors. • Background study • Feasibility study AGU Meeting Baltimore

  27. Planned Detector Design and Location Now 10 kiloton AGU Meeting Baltimore - Designed as 4 kton liquid scintillator detector. - Detection reaction: Oahu Pier construction Constraint! Big Island Hanohano Design not completely set yet! 4 km depth

  28. U and Th in the EarthChondritic Meteorites • U and Th concentrations in the Earth are based on measurement of chondritic meteorites. • Chondritic meteorites consist of elements similar to those in the solar photosphere. • Th/U ratio is 3.9 • Th/U ratio is known better than the absolute concentrations. AGU Meeting Baltimore

  29. Reference Earth ModelConcentrations of U and Th • Total amounts of U and Th in the Earth are estimated from the condritic • meteorites. • Concentrations in the sediments and crusts are based on the samples • on the surface, seismic data, and tectonic model. • Concentrations in the mantle are estimated by subtracting the amounts in • the sediments and the crusts. AGU Meeting Baltimore

  30. Is the Event Excess for Real and if So, What is the Source ? • The possible surplus of detected events implies that there may be another source of anti-neutrinos that have not been accounted for. • Proposed 3-10 TW georeactor if exists would produce anti-neutrino signal of 4-14% of the KamLAND signal. • The goal is to set an upper limit on the power of the hypothetical geo-reactor. AGU Meeting Baltimore Is it there and if so, how large is it?

  31. Expected Anti-neutrino Flux from Man-made reactors and Geo-reactor E > 2.4 MeV • Reactor spectrum for the deep Earth reactor is assumed to be a typical commercial reactor spectrum. • It is assumed that its output is very stable (on the data taking scale) AGU Meeting Baltimore 0.0137 events/TW·day 0.0102 events/TW·day • - 79% is within range 138-214km • ave. dist. 180 km • - Expected number of events in 515.1 days of livetime: • 365 + 23.7 (syst) 493.2 + 32.0 (syst.) • in the unoscillated case. E > 3.4 MeV E > 2.4 MeV

  32. Energy Spectrum for the Best Fit Result Observed spectrum is time integrated, while the best fit is obtained from the time varying maximum likelihood function best fit. PRELIMINARY AGU Meeting Baltimore

  33. The Δχ2 Test as a Function of Geo-reactor Power The best fit with SNO old (2003) choice of mixing parameters PRELIMINARY AGU Meeting Baltimore Very wide minimum

  34. Comparison of the Best Fit Result with Geological Data PRELIMINARY 31-44 TW AGU Meeting Baltimore 19-31 TW 0-12 TW

  35. Geoneutrino References • G. Marx, Menyhard N, Mitteilungen der Sternwarte, Budapest No. 48 (1960) • M.A. Markov, Neutrino, Ed. "Nauka", Moscow, 1964 • G. Eders, Nucl. Phys., 78 (1966) 657 • G. Marx, Czech. J. of Physics B, 19 (1969) 1471 • G. Marx and I. Lux, Acta Phys. Acad. Hung., 28 (1970) 63 • C. Avilez et al., Phys. Rev. D23 (1981) 1116 • L. Krauss et al., Nature 310 (1984) 191 • J.S. Kargel and J.S. Lewis, Icarus 105 (1993) 1 • R.S. Raghavan et al., Phys. Rev. Lett. 80 (1998) 635 • C.G. Rothschild, M.C. Chen, F.P. Calaprice, Geophys. Rev. Lett. 25 (1998) 1083 • F. Montovani et al., Phys. Rev. D69 (2004) 013001 AGU Meeting Baltimore

  36. Direct Measurement of U/Th Content - Anti-neutrinos (geo-neutrinos) are emitted in the decay chains of 40K, 232Th, 238U • Anti-neutrinos are highly penetrating particles • Anti-neutrinos can engage in inverse β-decay reaction • Only U and Th geo-neutrinos can be detected this way • KamLAND detector is an anti-neutrino detector • From the geo-neutrino flux detected in KamLAND, inferences about U/Th content can be made. Inv. Beta does not work for 40K! AGU Meeting Baltimore Inverse β-decay energy threshold 1.8 MeV.

  37. Detection Reaction in KamLAND e p  e- + n Ethreshold = 1.806 MeV • Inverse beta decay reaction combined with delayed neutron capture reaction. • Distinctive signature in time and space: Prompt event: e+ - e- annihilation – 2 γ rays Delayed event: 2.2 MeV γ ray about 200 μs later. Prompt Event γ γ e+ γ νe AGU Meeting Baltimore p n 2.2MeV Eprompt = E - 0.8 MeV 200 μs Delayed Event

  38. Uranium in the Core? • Radical hypothesis… not geologists paradigm • Natural nuclear reactor with power up to 10 TW operating in the center of the Earth, proposed by M. Herndon as the energy source of geo-magnetic field. • Although not a mainstream theory, not ruled out by any evidence. • If the geo-reactor exists, its anti-neutrino flux is visible in KamLAND! • If discovered, geo-reactor would revolutionize geology in the same way plate tectonics did: dramatic changes in understanding of the Earth formation and deep-Earth composition. AGU Meeting Baltimore

  39. Geo-reactor Pros and Cons • …requires substationally different inner core content: • Traditional Model (BSE): content of the inner core based on carbonaceous, chondrites. As a result, U and Th are in the form of oxides, act as lithophiles and can exist in the crust and mantle only. • Nuclear Earth Model (by M. Herndon): content of the inner core based on rare enstatite chondrites. U and Th are alloyed with Fe or S, act as siderophiles and due to high density can exist in the inner core and particularly the Earth’s center. …can explain the following unresolved question: - provide the energy source for driving the Earth’s magnetic field (0.02-10 TW of power running for more than 3 billion years!!!). - perhaps explains reversals of the geo-magnetic field (171 reversals recorded in the last 70 million years). - provide explanation for the up to 40 times higher measured ratios (comparing to average atmospheric ratio) of 3He/4He observed in volcanic plumes in Hawaii, Iceland some other places. AGU Meeting Baltimore

  40. accidentalcoincidencevertices Event Selection • Fiducial Volume • Muon Spallation Cut (9Li etc) • Coincidence Event Selection • selects500 cm radius from center • removes 120 cm radius from vertical axis • 2sec full volume veto following showering muons • 2sec 3m-cylindrical veto following non-showering muons • Distance： 0 < ΔR < 100cm • Interval： 0.5 μsec < ΔT < 1000 μsec • Delayed Signal Energy： 1.8 MeV < Edelayed < 2.6 MeV AGU Meeting Baltimore 152 events observed

  41. Background Summary • Neutrinos • Reactor: 80.4±7.2 • Spent Fuel : 1.9±0.2 • Cosmic Muon Induced • Fast neutrons (from outside): < 0.1 • Spallation products (9Li): 0.30±0.047 • Radioactive Impurity • Accidental coincidence 2.38±0.0077 • Cascade decay negligible • Spontaneous fission < 0.1 • (α,n) reaction 42.4±11.1 • (γ,n) reactionnegligible AGU Meeting Baltimore 152 eventsobserved total: 127.4 ± 13.3 (syst.)

  42. Effects of Location on Geo-neutrino Detection KamLAND Hawaii AGU Meeting Baltimore Sea of Japan KamLAND Geological Setting • Boundary of Continent and Ocean • Island Arc • Zn, Pb, limestone mine (skarn) • Sensitivity to mantle neutrinos small, • due to the vicinity of continental crust JapanTrench

  43. Unbinned Spectrum-Shape Analysis • Comparison of energy spectrum of observed events with expectation. Incorporates Th/U = 3.9constraint AGU Meeting Baltimore • KamLAND result: (25 ) • 90% confidence interval: 4.5 to 54.2 • 99% C.L. upper limit：70.7 • Ngeo=0 excluded at 95.3%(1.99σ)

  44. Number of observed events (1/MeV) Motivation for Geo-reactor Search Observed spectrum; Same shape for commercial reactors and geo-reactor. • Rate from the putative geo-reactor very small! • Incoming daily flux varies due to nuclear reactors varying work regime. E (MeV) Large error! 90% C.L. AGU Meeting Baltimore Small positive offset of 0.03e/day with VERY LARGE ERROR may be present, for 0 ev/day expected!

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