Geoneutrino Overview
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Transcript of Geoneutrino Overview
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