Geoneutrino Overview

Sanshiro EnomotoKamLAND CollaborationRCNS, Tohoku University

1 ． Review of Geoneutrino Physics (with KamLAND)2 ． KamLAND Result and Prospects3 ． Physics with Proposed Detectors

Neutrino Science 2007 – Deep Ocean Anti-Neutrino Observatory Workshop, Univ. of Hawaii at Manoa, March 23-25 2007

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)]

e4040

e4208232

e-4206238

νeCaK

ν4e4He6PbTh

ν6e 6 He8PbU

nepe

Threshold: 1.8 MeV

KamLAND: The First Detector Sensitive to Geoneutrinos

• Yields light on ionization (8000 photons / MeV)• Mainly consists of only C and H

20m

Liquid Scintillator

O

N

1.5g/l

HHHHHHHHHHHHHCCCCCCCCCCCCH HHHHHHHHHHHH

80%

CH3CH3

CH320%

Liquid Scintillator 1000 tonContained in plastic balloon

17-inch PMT 132520-inch 554

Detector Center

Surrounded by

(PMT : Photo Multiplier Tube, a photo sensor)

KamLAND Location

JapanTrench

Sea of Japan

You are here

Geological Setting• Boundary of Continent and Ocean• Island Arc (Orogenic)• ‘Hida’ Metamorphic Zone• Zn, Pb, limestone mine (skarn)• Surrounded by Gneiss Rocks

KamLAND

KamLAND

KamLAND is surrounded bya number of nuclear reactors

First Result from KamLAND

• Fiducial Volume: 408 ton• Live-time: 749 days• Efficiency: 68.7%

Expected Geoneutrinos• U-Series ： 14.9• Th-Series ： 4.0

Backgrounds• Reactor ： 82.3±7.2• (α,n) ： 42.4±11.1• Accidental ： 2.38±0.01

BG total ： 127.4±13.3Observed ： 152

Number of Geoneutrinos:＋ 19－ 1825

[T. Araki et al. (2005)]

Expected Geoneutrino Flux•U-Series 2.3x106 [1/cm2/sec]•Th-Series 2.0x106 [1/cm2/sec]

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

With 1032 target protons,•U-Series 32 events / year•Th-Series ８ events / year

Geoneutrino Origination PointsDetectable at KamLAND (MC)

South AmericaAntarctic

Australia

KamLAND

Greenland

50% within 500km25% from Mantle

Total 19 is predictedfor KamLAND 749 days

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

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

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

CRUST2.0

Zhao et al. (1992)

Comparison of CRUST 2.0 and Zhao et al.

Propagation of crustal thickness error

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%

Flux Prediction from Earth Models

Scale Bulk Composition

Fix Crustal Composition,Parameterize Mantle

U+Th Mass [kg]

Geoneutr

ino F

lux

[1/c

m2/s

ec]

KamLAND Result

• Fiducial Volume: 408 ton• Live-time: 749 days• Efficiency: 68.7%

Expected Geoneutrinos• U-Series ： 14.9• Th-Series ： 4.0

Backgrounds• Reactor ： 82.3±7.2• (α,n) ： 42.4±11.1• Accidental ： 2.38±0.01

BG total ： 127.4±13.3

Observed ： 152

Number of Geoneutrinos:＋ 19－ 1825

[T. Araki et al. (2005)]

KamLAND Spectrum Analysis

• Number of Geoneutrinos ： 28.0 • 99% C.L. upper limit ： 70.7 events• Significance 95.3% (1.99-sigmas)

＋ 15.6－ 14.6

Parameters NU, NTh: Number of Geoneutrinos sin22θ, Δm2 : Neutrino Oscillation α1, α2: Backgrounds Uncertainties

• KamLAND is insensitive to U/Th ratio→ adopt U/Th ~ 3.9 from Earth science

Discrimination of U and Th

Tota

l Num

ber o

f U a

nd T

h

Comparison with Earth Model Predictions

• Consistent with BSE model predictions• 99%C.L. upper limit too large to be converted to heat production (No Earth models applicable)

U+Th Mass [kg]

Geoneutr

ino F

lux

[1/c

m2/s

ec]

Earth Model Prediction

KamLAND 1-σ Range

KamLAND 99% Limit

KamLAND Problem

ReactorNeutrinoBG

(α,n) BG

206Pb210Bi 210Po

210Pb

5.013 d

22.3 y

stable138.4 d

222Rn3.8 d 13C (α,n) 16O n + p → n + p

210Po decay rate error 14%

Cross-section error: 20%

Quenting factor error: 10%

KamLAND Prospects (1)

• 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%

(α,n) Background error had been reduced

Po-C Calibration (MC/Data)P quenching measurement

KamLAND Prospects (2)

LS Distillation in Progress⇒ removes radioactivity by 10-5

Another 749 days operation after purification,• Error is reduced ： from 54% to 28% (error is dominated by reactor neutrinos)• Significance ： 99.96%

we remove these

BEFORE AFTER

KamLAND Prospects

28% uncertainty

Upper limit (~40TW)comparable withheat flow (~40TW)

Future Geoneutrino Experiments

Project LocationMass(kton)

Depth(m.w.e.)

KamLAND Kamioka / Japan 1.0 2700

Borexino Gran Sasso / Italy 0.3 3700

SNO+ Sudbury / Canada 0.7 5400

Hano-hano Hawaii / U.S. 10 4000

BNO Baksan / Russia 1.0 4800

LENAPhyasalm / FinlandNestor / Greece

5040004000

HSDKimballton / U.S.Homestake / U.S.Soudan / U.S.

100185042002070

The World Map of Geoneutrino Flux

from Crust 30~70 /1032P/year

from Mantle ~10 /1032P/year

Typical Rate

Reactor Neutrino Backgrounds

KamLAND-II 750 days（ expected ）

without reactor BG

The World Map of Geoneutrino S/N Ratio

Geoneutrino Flux @ Future Detector Sites

KamLAND

Borexino Hanohano

SNO+

LENA

Required Exposure for 20% precision determination

on CC, estimate BSE 0.5~1 [1032P ・ year]

on CC, estimate M ~30 [1032P ・ year]

on OC, estimate M 4.5 [1032P ・ year]

Typical Time

Sensitive toCrustal Composition

Sensitive toMantle Composition

Worst Place

Sensitivity to “Regional” Structure

Kamioka / Island Arc Gran Sasso / Mesozoic Crust

Sudbury / Archean CrustHawaii / Oceanic Island

• 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.

Plumes, Ocean Ridges, …

Neutrino Detector on Plume

Neutrino Detector on Mid-Ocean Ridge

At Tahiti, 13% comes from “hot” mantle⇒ sensitive to a factor enrichment

If the mantle beneath mid-ocean ridgeIs depleted by a factor, it should be visible

Portable detector (like Hanohano)will open new application

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

Backup Slides

Appendix

Geoneutrino Spectrum

Geoneutrino Angular Distribution at Kamioka