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Geoneutrino Overview
1．Review of Geoneutrino Physics (with KamLAND)
2．KamLAND Result and Prospects
3．Physics with Proposed Detectors
Sanshiro Enomoto
KamLAND Collaboration
RCNS, Tohoku University
Neutrino Science 2007 – Deep Ocean Anti-Neutrino Observatory Workshop, Univ. of Hawaii at Manoa, March 23-25 2007
Geoneutrinos
• Geoneutrinos are produced by
238
U
232
Th 
40
K
206
40
Pb  8 4 He  6 e -  6 ν e
208
Pb  6 4 He  4 e   4 ν e
Ca  e   ν e
– Direct measurement of HPE
– U:~8TW, Th: ~8TW, K: ~3TW
• Geoneutrinos are detected by
 e  p  e  n
– Two consecutive signals
– Threshold 1.8 MeV
– Not sensitive to 40K;
other targets discussed
[M.C.Chen (2005)]
Threshold: 1.8 MeV
KamLAND: The First Detector Sensitive to Geoneutrinos
Detector Center
Liquid Scintillator 1000 ton
Contained in plastic balloon
Surrounded by
17-inch PMT 1325
20-inch
554
(PMT : Photo Multiplier Tube, a photo sensor)
Liquid Scintillator
CH3
CH3
CH3
HHHHHHHHHHHH
HCCCCCCCCCCCCH
HHHHHHHHHHHH
80%
N
O
1.5g/l
20%
20m
• Yields light on ionization (8000 photons / MeV)
• Mainly consists of only C and H
KamLAND Location
Geological Setting
KamLAND
• Boundary of Continent and Ocean
• Island Arc (Orogenic)
• ‘Hida’ Metamorphic Zone
• Zn, Pb, limestone mine (skarn)
• Surrounded by Gneiss Rocks
You are here
Sea of Japan
KamLAND
Japan
Trench
KamLAND is surrounded by
a number of nuclear reactors
First Result from KamLAND
• Fiducial Volume: 408 ton
• Live-time:
749 days
• Efficiency:
68.7%
[T. Araki et al. (2005)]
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:
25
＋19
－18
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
Geoneutrino Origination Points
Detectable at KamLAND (MC)
KamLAND
50% within 500km
25% from Mantle
Australia
Greenland
Antarctic
South America
Expected Geoneutrino Flux
•U-Series
2.3x106 [1/cm2/sec]
•Th-Series
2.0x106 [1/cm2/sec]
With 1032 target protons,
•U-Series
32 events / year
•Th-Series
８ events / year
Total 19 is predicted
for KamLAND 749 days
Uncertainties of the Model
• Geochemical / Geophysical data
rarely 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
~500km
• 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 ???
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
Comparison of CRUST 2.0 and Zhao et al.
CRUST2.0
Propagation of crustal thickness error
Zhao et al. (1992)
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%
Geoneutrino Flux [1/cm2/sec]
Flux Prediction from Earth Models
Scale Bulk Composition
Fix Crustal Composition,
Parameterize Mantle
U+Th Mass [kg]
KamLAND Result
[T. Araki et al. (2005)]
• 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:
25
＋19
－18
KamLAND Spectrum Analysis
Parameters
NU, NTh:
Number of Geoneutrinos
sin22θ, Δm2 : Neutrino Oscillation
α 1, α 2:
Backgrounds Uncertainties
Total Number of U and Th
• KamLAND is insensitive to U/Th ratio
→ adopt U/Th ~ 3.9 from Earth science
• Number of Geoneutrinos：28.0 ＋15.6
－14.6
• 99% C.L. upper limit：70.7 events
• Significance 95.3% (1.99-sigmas)
Discrimination of U and Th
Geoneutrino Flux [1/cm2/sec]
Comparison with Earth Model Predictions
KamLAND 99% Limit
KamLAND 1-σ Range
Earth Model Prediction
U+Th Mass [kg]
• Consistent with BSE model predictions
• 99%C.L. upper limit too large to be converted to heat production
(No Earth models applicable)
KamLAND Problem
(α,n) BG
Reactor
Neutrino
BG
210Pb
222Rn
22.3 y
3.8 d
210Bi
5.013 d
210Po
210Po
138.4 d
206Pb
stable
decay rate error 14%
13C
(α,n) 16O
n+p→n+p
Cross-section error: 20%
Quenting factor error: 10%
KamLAND Prospects (1)
(α,n) Background error had been reduced
• 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%
P quenching measurement
Po-C Calibration (MC/Data)
KamLAND Prospects (2)
LS Distillation in Progress
⇒ removes radioactivity by 10-5
we remove these
BEFORE
AFTER
Another 749 days operation after purification,
• Error is reduced：from 54% to 28% (error is dominated by reactor neutrinos)
• Significance： 99.96%
KamLAND Prospects
Upper limit (~40TW)
comparable with
heat flow (~40TW)
28% uncertainty
Future Geoneutrino Experiments
Mass
(kton)
Depth
(m.w.e.)
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
LENA
Phyasalm / Finland
Nestor / Greece
50
4000
4000
HSD
Kimballton / U.S.
Homestake / U.S.
Soudan / U.S.
100
1850
4200
2070
Project
Location
KamLAND
The World Map of Geoneutrino Flux
Typical Rate
from Crust
30~70 /1032P/year
from Mantle
~10 /1032P/year
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
SNO+
LENA
Borexino
Hanohano
Required Exposure for 20% precision determination
Typical Time
on CC, estimate BSE
0.5~1 [1032P・year]
Sensitive to
Crustal Composition
on CC, estimate M
~30 [1032P・year]
on OC, estimate M
4.5 [1032P・year]
Worst Place
Sensitive to
Mantle Composition
Sensitivity to “Regional” Structure
Kamioka / Island Arc
Gran Sasso / Mesozoic Crust
Hawaii / Oceanic Island
Sudbury / Archean Crust
• 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
At Tahiti, 13% comes from “hot” mantle
⇒ sensitive to a factor enrichment
Neutrino Detector on
Mid-Ocean Ridge
If the mantle beneath mid-ocean ridge
Is 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
Appendix
Backup Slides
Geoneutrino Spectrum
Geoneutrino Angular Distribution at Kamioka