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

Geo-neutrino: ExperimentsJelena Maricic

Drexel UniversityNeutrino Champagne – LowNu2009

October 20, 2009

ννν ν

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νν

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

10/20/2009 2J. Maricic, Drexel University

GEOLOGICAL MOTIVATION FOR GEO-NEUTRINOS

Geologists agree! We know more about the Sun than about Earth under our feet

10/20/2009 3J. Maricic, Drexel University

What and How We Learn About Earth Interior?

J. Maricic, Drexel University 4

• 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 10/20/2009

10/20/2009 J. Maricic, Drexel University5

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?

10/20/2009 J. Maricic, Drexel University6

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!

Only good fordetection of neutrinos with energies > 1.8 MeV.

Inv. does not work for 40K!

e p+ e+ + n

Inv. reaction:

10/20/2009 J. Maricic, Drexel University 7

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

Geo-neutrinos provide a direct method – instantaneous information about full radioactive heat production from 232Th and 238U from ENTIREENTIRE Earth.

- 232Th and 238U fluxes provide evidence about the amounts and distribution

(crust, mantle, or even core) of 238U and 232Th - - uniqueunique 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


KamLAND: reactor

vs. geo-neutrinos

• KamLAND – 1 kton scintillator detector • Detects electron anti-neutrinos via inverse beta decay10/20/2009

J. Maricic, Drexel University 9

n

e+γ

γ

γνe

2.2MeV

PromptEvent

Delayed Event

p

200 μs

p

Reactor BackgroundReactor Backgroundwith oscillationwith oscillation

GeoneutrinosGeoneutrinos


Crust vs. Mantle Geo-Neutrinos at KamLANDCrust vs. Mantle Geo-Neutrinos at KamLAND

JapanTrench

Sea of JapanGeological Setting• Boundary of Continent and Ocean• Island Arc• Zn, Pb, limestone mine (skarn)

KamLAND

KamLAND

Crust thickness:- continental ~40 km- oceanic ~8 km

U, Th are lithophile: strong tendency to leave the mantle andstay in the crustU, Th more abundant in the crust

Sensitivity to mantle Sensitivity to mantle neutrinos small, neutrinos small, due to the vicinity of due to the vicinity of continental crustcontinental crust

S. Enomoto

S. Enomoto


Local vs. Global Neutrinos at KamLAND

Kamioka MineHida Metamorphic Zone

Japan Island Arc‘Earth around Japan’

KamLAND is looking atKamLAND is looking at‘‘Earth around JapanEarth around Japan’,’,

if local variation is averaged enoughif local variation is averaged enough

Assuming uniform crustal composition(no local variation)!

50% of flux within500 km from KL.Geoneutrinos from the crust dominant!

50% of flux within500 km from KL.Geoneutrinos from the crust dominant!

S. Enomoto


Expected Neutrino Spectrum at KamLANDExpected Neutrino Spectrum at KamLAND

Expected event rate: U series: 14.9 Th series: 4.0 Reactor (E<3.4MeV): 80.4

Geo-neutrinoanalysis window

Reactor neutrinoanalysis window

U/Th flux smallcomparing to reactorflux and bkgs.

U/Th flux smallcomparing to reactorflux and bkgs.

Reactor

Accidental

(,n)

Total BG

Geoneutrinos + BG

Antineutrinos coming from nuclear reactors around Japan present the largest source of bkg in KamLAND.

*749.14 days of livetime

Poor signal to bkg ratio!


Analysis Results (749.14 days livetime)Analysis Results (749.14 days livetime)

Comparison of energy spectrum of observed events with expectation.

• 90% confidence interval: 4.5 to 54.2 • 99% C.L. upper limit ： 70.7 • Ngeo=0 excluded at 95.3%(1.99σ)

• 90% confidence interval: 4.5 to 54.2 • 99% C.L. upper limit ： 70.7 • Ngeo=0 excluded at 95.3%(1.99σ)

Incorporates Th/U = 3.9 constraint

Best fit pointBest fit point

Unbinned spectrum-shape MaximumLikelihood method used for analysis.

Geophysical model GoodAgreement

GoodAgreement

Observed: (25 ) events +19- 18

Confirmation101 years after Rutherford proposed radioactivity as the source of Earth’s heat


KamLAND KamLAND Results (2008)Results (2008)

- Enlarged fiducial volume (6 m Enlarged fiducial volume (6 m vs. 4.5 m)vs. 4.5 m)

- - Livetime: 1491 days Livetime: 1491 days

- Analysis threshold: 0.9 MeV - Analysis threshold: 0.9 MeV

- Geonu flux from Enomoto - Geonu flux from Enomoto et et alal..

model: 16TW U+Th totalmodel: 16TW U+Th total

- U&Th strongly U&Th strongly anti-correlatedanti-correlated

Events

Model

U/Th

56.6

13.1

Best fitBest fit

U/ThU/Th

2525

3636

Fit with3.9 Fit with3.9 ratio fixedratio fixed

73±2773±27

Model

Data Fit


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 (66) TWand 90% C.L. limit 19 TWwith 515 days of livetime (2005)

The best fit value (04) TWand 90% C.L. limit 6.2 TWwith 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)


Scintillator purificationdecreased it - 1/10 or better

Reactor flux~50% in last2 years

PROSPECTS WITH OTHER RUNNING AND PLANNED NEUTRINO EXPERIMENTS

What it takes for precision measurement


BNO

Locations for Possible Geonu ExperimentsLocations 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 HawaiiKamLAND Japan

HanohanoKamLAND

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

HawaiiHanohano

Commercial nuclear reactor background

JapanKamLAND

Reactor Reactor BackgroundBackgroundwith oscillationwith oscillation

GeoneutrinosGeoneutrinos

KamLAND

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)

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)


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.


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)10/20/2009 J. Maricic, Drexel University 24

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)


POTASSIUM 40What geologists would really like to know


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


IMPROVING DETECTION TECHNIQUE WITH DIRECTIONALITY

Uncovering neutrino detection in scintillation detectors


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


n

e+γ

γ

γνe

2.2MeV

PromptEvent

Delayed Event

p

200 μs

p

S. Enomoto


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…




Documents

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