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

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 10/20/20092J. Maricic, Drexel University

GEOLOGICAL MOTIVATION FOR GEO-NEUTRINOS Geologists agree! We know more about the Sun than about Earth under our feet 10/20/20093J. Maricic, Drexel University

What and How We Learn About Earth Interior? J. Maricic, Drexel University4 Chemical composition: – Depth up to 670 km studied directly: melts or drilling (12km). – Deep Earth inaccessible. Guess composition by abundances in meteorites and sun. ( km) 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: – TW. Not well constrained due to model dependence (maybe TW ?!?) – TW are from radioactivity in 40 K, 232 Th, 238 U (trace elements); predominant heat source 10/20/2009

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 U, Th, K? Deep core fission reactor?

10/20/2009J. Maricic, Drexel University 6 Direct Measurement of U/Th Content with Geoneutrinos -Antineutrinos (geo-neutrinos) are emitted in the decay chains of 40 K, 232 Th, 238 U - Low energy < 3.4 MeV; 232 Th neutrinos have lower end point than 238 U 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! Only good for detection of neutrinos with energies > 1.8 MeV. Inv.  does not work for 40 K!  e  p +  e + + n Inv.  reaction:

10/20/2009J. Maricic, Drexel University7 Geo-neutrinos vs. Conventional Geological Tools in 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 ENTIRE Geo-neutrinos provide a direct method – instantaneous information about full radioactive heat production from 232 Th and 238 U from ENTIRE Earth Th and 238 U fluxes provide evidence about the amounts and distribution (crust, mantle, or even core) of 238 U and 232 Th - unique - 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

EXPERIMENTAL DETECTION OF GEO- NEUTRINOS AND SEARCH FOR GEO- REACTOR WITH KAMLAND EXPERIMENT How even crude measurement is very exciting 10/20/2009J. Maricic, Drexel University8

KamLAND: reactor vs. geo-neutrinos KamLAND – 1 kton scintillator detector Detects electron anti-neutrinos via inverse beta decay 10/20/2009 J. Maricic, Drexel University9 n e+e+ γ γ γ νeνe 2.2MeV Prompt Event Delayed Event p 200 μs p Reactor Background with oscillation Geoneutrinos

10/20/2009J. Maricic, Drexel University10 Crust vs. Mantle Geo-Neutrinos at KamLAND Japan Trench Sea of Japan Geological Setting Boundary of Continent and Ocean Island Arc Zn, Pb, limestone mine (skarn) KamLAND 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 S. Enomoto

10/20/2009J. Maricic, Drexel University11 Local vs. Global Neutrinos at KamLAND Kamioka Mine Hida Metamorphic Zone Japan Island Arc ‘Earth around Japan’ KamLAND is looking at ‘Earth around Japan’, if local variation is averaged enough Assuming uniform crustal composition (no local variation)! 50% of flux within 500 km from KL. Geoneutrinos from the crust dominant! S. Enomoto

10/20/2009J. Maricic, Drexel University12 Expected Neutrino Spectrum at KamLAND Expected event rate: U series: 14.9 Th series: 4.0 Reactor (E<3.4MeV) : 80.4 Geo-neutrino analysis window Reactor neutrino analysis window U/Th flux small comparing to reactor flux and bkgs. Reactor Accidental ( ,n) Total BG Geoneutrinos + BG Antineutrinos coming from nuclear reactors around Japan present the largest source of bkg in KamLAND. * days of livetime Poor signal to bkg ratio!

10/20/2009 J. Maricic, Drexel University 13 Analysis Results ( days livetime) Comparison of energy spectrum of observed events with expectation. 90% confidence interval: 4.5 to % C.L. upper limit ： 70.7 N geo =0 excluded at 95.3%(1.99σ) Incorporates Th/U = 3.9 constraint Best fit point Unbinned spectrum-shape Maximum Likelihood method used for analysis. Geophysical model Good Agreement Observed: (25 ) events Confirmation 101 years after Rutherford proposed radioactivity as the source of Earth’s heat

10/20/2009J. Maricic, Drexel University 14 KamLAND Results (2008) Enlarged fiducial volume (6 m vs. 4.5 m) - Enlarged fiducial volume (6 m vs. 4.5 m) - Livetime: 1491 days - Analysis threshold: 0.9 MeV - Geonu flux from Enomoto et al. model: 16TW U+Th total model: 16TW U+Th total -U&Th strongly anti-correlated Events Model U/Th Best fit U/Th2536 Fit with3.9 ratio fixed 73±27 Model Data Fit

10/20/2009J. Maricic, Drexel University15 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: 68% 90% First results New results The best fit value (6  6) TW and 90% C.L. limit 19 TW with 515 days of livetime (2005) The best fit value (0  4) TW and 90% C.L. limit 6.2 TW with 1491 days of livetime (2008)

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) 10/20/2009J. Maricic, Drexel University16 Scintillator purification decreased it - 1/10 or better Reactor flux ~50% in last 2 years

PROSPECTS WITH OTHER RUNNING AND PLANNED NEUTRINO EXPERIMENTS What it takes for precision measurement 10/20/2009J. Maricic, Drexel University17 BNO

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

Geonu Crust and Mantle Signal at Various Detector Sites Hanohano Hawaii KamLAND Japan Hanohano KamLAND 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 Canada S. Enomoto M. Chen

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

Borexino experiment 10/20/2009J. Maricic, Drexel University 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 (2006) - arXiv:hep-ex/ ) Geo-reactor signal: 5-21% of reactor signal (1-6 TW)

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 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) 10/20/2009J. Maricic, Drexel University22

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. 10/20/2009J. Maricic, Drexel University23

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 events/year ( K. A. Hochmuth et al. - Astropart.Phys. 27 (2007) – arXiv:hep-ph/ ) LS loaded with 0.1% Gd Geo-reactor signal: 6.2 – 37.5% of reactor signal (1 – 6 TW) 10/20/2009J. Maricic, Drexel University24

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) 10/20/2009J. Maricic, Drexel University25

POTASSIUM 40 What geologists would really like to know 10/20/2009J. Maricic, Drexel University26

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 Q b and low ft elements searched like 106 Cd(see M. Chen, Neutrino Sciences 2005) and many others (Kobayashi et al, Geophys. Res. Lett 18(633) /20/2009J. Maricic, Drexel University27

IMPROVING DETECTION TECHNIQUE WITH DIRECTIONALITY Uncovering neutrino detection in scintillation detectors 10/20/2009J. Maricic, Drexel University28

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 10/20/2009J. Maricic, Drexel University29 n e+e+ γ γ γ νeνe 2.2MeV Prompt Event Delayed Event p 200 μs p S. Enomoto

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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… 10/20/2009J. Maricic, Drexel University31

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