Transcript KamLAND Detector

KamLAND and Geoneutrinos
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4.
Review of Previous Results
Recent Improvements (Preliminary)
Future Prospects
Far Future Dreams
Sanshiro Enomoto
KamLAND Collaboration
RCNS, Tohoku University
Applied Antineutrino Physics 2007, APC Laboratory Paris, December 13-14 2007
KamLAND Experiment
• observes low energy anti-neutrinos in the Kamioka Mine, Hida, Japan
• consists of 1000ton Liquid Scintillator, surrounded by 1845 PMT’s
Kamioka Mine
1000m
Reaction:
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2002
2002
2005
2005
2007
Jan:
Dec:
Jan:
Jul:
Dec:
Start data taking
Evidence for reactor neutrino disappearance (145 days)
Evidence of reactor neutrino spectral distortion (514 days)
Investigation of geoneutrinos (749 days)
1491 day data accumulated
KamLAND Detector
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
PC: 20%
CH3
CH3
CH3
20m
dodecane: 20%
HHHHHHHHHHHH
HCCCCCCCCCCCCH
HHHHHHHHHHHH
80%
PPO: 1.5 g/l
N
O
1.5g/l
20% light on ionization (8000 photons / MeV)
• Yields
• Mainly consists of only C and H
Antineutrino Detection Method
 e  p  e  n
τ~210 μsec
e   e   2 (0.511MeV)
Ethreshold  1.8 MeV
Eprompt  E e  0.8 MeV
n  p  d   (2.2MeV)
Edelayed  2.2 MeV
Two characteristic signals
Clear event identification
Great BG suppression
time
τ~210 μsec
KamLAND Detector
Kamioka Mine
KamLAND Inner View
Japan Arc
KamLAND Outer View
Scintillator Container
Photo Multiplier Tube
Antineutrino Sources
HPE (U/Th) in the Earth
~50% from
surrounding crust
~25% from
mantle
238
U
232
Th 
Pb  8 4 He  6 e-  6 ν e
206
Pb  6 4 He  4 e   4 ν e
208
Nuclear Power Reactors
Reactor Neutrino Flux Calculation
Example of Reactor Operation Data
• Japanese Reactors (95.5%):
Operation data, including
fuel burn-up, for each core
are provided by operators.
Neutrino Flux at KamLAND
(no oscillation case)
• Korean Reactors (3.4%):
Flux are calculated based on
published electrical output
• Other Reactors (1.1%):
Nominal power is assumed
Total ~2% error (conservative)
Geoneutrino Flux Prediction
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[Earth.Plan.Sci.Lett, 258, 147 (2007)]
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
KamLAND Antineutrino Spectrum (expected)
 e  p  e  n
Ethreshold  1.8 MeV
Eprompt  E e  0.8 MeV
Neutrino Property Study
Geoneutrinos: Neutrino Application
• Direct measurement of HPE in the Earth
[Nature 436, 499 (2005)]
• Signature of Neutrino Oscillation
• Precision Measurement of Oscillation Parameters
[Phys.Rev.Lett. 94, 081801 (2005)]
Geoneutrino Expected Rate and Spectrum
• 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
First Geoneutrino Result
• Fiducial Volume: 408 ton
• Live-time:
749 days
• Efficiency:
68.7%
[Nature 436, 499 (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
Spectrum Analysis
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
• 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
Total Number of U and Th
Earth Model
Prediction
Geoneutrino Flux [1/cm2/sec]
Flux Prediction from Earth Models
Scale Bulk Composition
Fix Crustal Composition,
Parameterize Mantle
U+Th Mass [kg]
Geoneutrino Flux [1/cm2/sec]
Comparison with Earth Model Predictions
KamLAND 99% Limit
Total Terrestrial
Heat Flow (44TW)
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: Overwhelming Backgrounds
(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%
Improvements
(α,n) Background error reduced
• New (α,n) Cross section data available
• Vertex reconstruction improved (for 210Po decay rate)
• Proton quenching factor measured
• 210Po-13C source calibration performed
⇒ (α,n) error reduced from ~26% to ~11%
P quenching measurement
Po-C Calibration (MC/Data)
Improved Results (Preliminary)
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More statistics accumulated: 749 day to 1491 day
(α,n) error reduced: ~26% to ~11%
Reconstruction improved (off-axis calibration)
Analysis improved:
– Fiducial volume increased
– Time variation included
– Optimal event selection with figure-of-merit basis
Preliminary
Preliminary
Geophysics with Improved Results (Preliminary)
Preliminary
KamLAND 99% Limit
KamLAND 1-σ Range
Earth Model Prediction
• Error is reduced from 56% to 36%
• Consistent with BSE model predictions
• 99%C.L. upper limit is approaching to the total terrestrial heat
Future Prospects
LS Distillation in Progress
⇒ removes radioactivity by 10-5
we remove these
distilled scintillator
Preliminary
Future Prospects
Assuming:
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10-4 reduction of 210Pb
Enlarged fiducial volume (5.5m)
Improved selection criteria
749 days livetime
BEFORE
we remove these
AFTER
If combined with the current 1491 day data,
• Error is reduced：from 36% to 25% (error is dominated by reactor neutrinos)
• Significance： 99.992% (3.96 sigmas)
Future Prospects
749 days after purification, combined with current 1491 day data
99% upper limit
1.6 times above BSE
25% uncertainty
• Measurement error is comparable with Earth model predictions
• 99%C.L. limit can exclude some “upper limit” models
Far Future Dreams: Directional Sensitivity
Directional information provides:
・Rejection of backgrounds
・Separation of crust and mantle
・Earth tomography by multiple detectors
Good News:
・Recoiled neutron remembers direction
Bad News:
・Thermalization blurs the info
・Gamma diffusion spoils the info
・Reconstruction resolution is too poor
Wish List:
・large neutron capture cross-section
・(heavy) charged particle emission
and
・good resolution detector (~1cm)
Towards Directional Sensitivity 1
6Li
loading helps preserving directional information
• Large neutron capture cross-section: 940 barn
• 6Li + n → α + T : no gamma-ray emission
• Natural abundance 7.59%
Neutron Capture Position (MC)
Delayed Event Position (MC)
Various chemical forms for Li loading are being tested…
Towards Directional Sensitivity 2
~1M pixel imaging can achieve 1 cm resolution
• Proper optics need to be implemented
• Sensitivity to 1 p.e. and high-speed readout required
First step for LS imaging, just started…
image
lens intensifier
lens
10cm
LS
(Bis-MSB added)
Muon Event ???
lends image
intensifier
CCD
LS
CCD
Fresnel lens
Isotope Decay Event ???
Summary
• KamLAND, low-energy antineutrino detector,
– determined oscillation parameters precisely
– made first experimental investigation on geoneutrinos
• Recent updates with more stat. and less syst. err.,
– reduced geoneutrino measurement error from 54% to 36%
– Upper limit is comparable with Earth model limits
• Further LS purification is in progress
– will reduce error to ~25%
– Measurement error will be comparable with Earth models
• R&D for directional sensitivity underway