KamLAND and Geoneutrinos

Sanshiro EnomotoKamLAND CollaborationRCNS, Tohoku University

1. Review of Previous Results2. Recent Improvements (Preliminary)3. Future Prospects4. Far Future Dreams

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

Reaction:

1000m

Kamioka Mine

• 2002 Jan: Start data taking• 2002 Dec: Evidence for reactor neutrino disappearance (145 days)• 2005 Jan: Evidence of reactor neutrino spectral distortion (514 days)• 2005 Jul: Investigation of geoneutrinos (749 days)• 2007 Dec: 1491 day data accumulated

KamLAND Detector

• 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)

PC: 20% dodecane: 20% PPO: 1.5 g/l

Antineutrino Detection Method

time

MeV8.0prompt e

EE

τ~210 μsec

nepe

(2.2MeV) dpn

(0.511MeV)2 ee

MeV2.2delayed E

MeV8.1threshold E

τ~210 μsec

Two characteristic signals

Clear event identificationGreat BG suppression

KamLAND Detector

Japan ArcKamioka Mine

KamLAND Outer View

KamLAND Inner View

Photo Multiplier Tube

Scintillator Container

Antineutrino Sources

Nuclear Power ReactorsHPE (U/Th) in the Earth

~50% fromsurrounding crust

~25% frommantle

e4208232

e-4206238

ν4e4He6PbTh

ν6e 6 He8PbU

Reactor Neutrino Flux Calculation

Example of Reactor Operation Data

Neutrino Flux at KamLAND (no oscillation case)

• Japanese Reactors (95.5%): Operation data, including fuel burn-up, for each core are provided by operators.

• Korean Reactors (3.4%): Flux are calculated based on published electrical output

• Other Reactors (1.1%): Nominal power is assumed

Total ~2% error (conservative)

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

Geoneutrino Flux Prediction

• 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

[Earth.Plan.Sci.Lett, 258, 147 (2007)]

KamLAND Antineutrino Spectrum (expected)

MeV8.0prompt e

EE

nepe MeV8.1threshold E

Neutrino Property Study

• Signature of Neutrino Oscillation• Precision Measurement of Oscillation Parameters[Phys.Rev.Lett. 94, 081801 (2005)]

Geoneutrinos: Neutrino Application• Direct measurement of HPE in the Earth

[Nature 436, 499 (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%

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

[Nature 436, 499 (2005)]

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

Earth ModelPrediction

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]

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

Total TerrestrialHeat Flow (44TW)

KamLAND Problem: Overwhelming Backgrounds

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%

Improvements

• 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%

(α,n) Background error reduced

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

Improved Results (Preliminary)• 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)

Earth Model Prediction

KamLAND 1-σ Range

KamLAND 99% Limit

• Error is reduced from 56% to 36%• Consistent with BSE model predictions• 99%C.L. upper limit is approaching to the total terrestrial heat

Preliminary

Future Prospects

LS Distillation in Progress⇒ removes radioactivity by 10-5

we remove these

distilled scintillator

Preliminary

Future Prospects

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)

BEFOREAFTER

we remove these

Assuming:• 10-4 reduction of 210Pb• Enlarged fiducial volume (5.5m)• Improved selection criteria• 749 days livetime

Future Prospects

25% uncertainty

749 days after purification, combined with current 1491 day data

• Measurement error is comparable with Earth model predictions• 99%C.L. limit can exclude some “upper limit” models

99% upper limit1.6 times above BSE

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 emissionand・ good resolution detector (~1cm)

Towards Directional Sensitivity 1

Neutron Capture Position (MC) Delayed Event Position (MC)

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%

Various chemical forms for Li loading are being tested…

Towards Directional Sensitivity 2~1M pixel imaging can achieve 1 cm resolution

LS lends imageintensifier

10cm

CCD

lenslens

LS

imageintensifier

CCD

Fresnel lens

• Proper optics need to be implemented• Sensitivity to 1 p.e. and high-speed readout required

First step for LS imaging, just started…

Muon Event ??? Isotope Decay Event ???

(Bis-MSB added)

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