Experimental Status of Geo-reactor Search with KamLAND Detector Jelena Maričić University of Hawaii at Manoa

Experimental Status of Experimental Status of Geo-reactor SearchGeo-reactor Search

with with KamLAND DetectorKamLAND Detector

Jelena Maričić

University of Hawaii at Manoa

Neutrino Geophysics, Honolulu 2December, 15 2005

OutlineOutline

• KamLAND detector: design and features• Motivation for experimental geo-reactor search in

KamLAND• Geo-reactor analysis anti-neutrino event selection and backgrounds• Anti-neutrino flux at KamLAND• Analysis• Summary and conclusion


KamLAND Detector: Design and Features

KamLAND Detector: Design and Features


KamLAND: Purpose and Location

KamLAND: Purpose and Location

- KamLAND - anti-neutrino detector; built to study

anti-neutrino oscillations. - Japan - natural choice for

location of anti-neutrino detector :

- large number of nuclear plants. - Nuclear plants - the

largest man-made νe sources.

- Nuclear plant


Reactors as Neutrino Sources and KamLANDReactors as Neutrino Sources and KamLAND

• Nuclear reactor is an excellent source of electron anti-neutrinos from β decay.

• Average 3 GWth plant has a flux of 6•1020 anti-neutrinos/s!

• KamLAND - disappearance experiment

ννeeννee

ννee

ννee

ννee

ννee

ννee

ννeeνe detector

nucle

ar

nucle

ar

reacto

r

reacto

r

ννxx ??

LL

Look for a deficit of νe at a distance Lννee

KamLANDKamLAND


Anti-neutrino SpectrumAnti-neutrino Spectrum

E (MeV)

Nu

mb

er o

f ob

serv

ed e

ven

ts

(1/M

eV)

Observed spectrum

Interaction cross-section (~10-43cm2)

Reactorspectrum


Detector SchemeDetector Scheme• 1kton of LS surrounded

by buffer oil and acrylic Rn barrier.

• 1325 17” PMTs• 554 20” PMTs• 34% photocatode

coverage• 225 20” PMTs - veto water Cherenkov detector• 300 p.e./MeV observed at

the center. *KamLAND oil has the best

radiopurity ever achieved in the world: U (3.5 + 0.5) x 10-18 g/g

Th (5.2 + 0.8) x 10-17 g/gK < 2.7 x 10-16 g/g

Motivation for the Experimental Geo-reactor Search

with KamLAND

Motivation for the Experimental Geo-reactor Search

with KamLAND


IntroductionIntroduction

• Natural nuclear fission reactor with power up to 10 TW in the center of the Earth was proposed by M. Herndon as the energy source of geo-magnetic field.

• 4.5 billion years ago, 235U/238U ratio was high enough for the nuclear fission reaction to occur.

• If such a reactor exists, its anti-neutrino flux would be visible by KamLAND.

235U/238U > 5%

Fast breeder nuclear reactor was simulated using the SCALE code package (by D. Hollenback and M. Herndon) and shown feasibility and sustainability for 4.5 billion years.

Neutrino Geophysics, Honolulu 10

December, 15 2005

Motivation for Geo-reactor SearchMotivation for Geo-reactor Search

Small positive offset of 0.03e/daywith VERY LARGE ERROR may be present, for 0 ev/day expected!

Small positive offset of 0.03e/daywith VERY LARGE ERROR may be present, for 0 ev/day expected!

Large error!

90% C.L.

• Rate from the putative geo-reactor very small!

• Incoming daily flux varies due

to nuclear reactors varying work regime.


December, 15 2005

Is the Event Excess for Real and if So, What is the Source ?

Is the Event Excess for Real and if So, What is the Source ?

• The possible surplus of detected events implies that there may be another source of anti-neutrinos that have not been accounted for.

• Proposed 3-10 TW georeactor if exists would produce anti-neutrino signal of 4-14% of the KamLAND signal.

• The goal of this analysis is to set the upper limit on the power

of the putative geo-reactor.

Is it there and if so, how large is it?


December, 15 2005

Geo-reactor Analysis Anti-neutrino Event

Selection and

Backgrounds

Geo-reactor Analysis Anti-neutrino Event

Selection and

Backgrounds


December, 15 2005

Detection Reaction in KamLANDDetection Reaction in KamLAND• Inverse beta decay reaction

combined with delayed neutron capture reaction.

• Distinctive signature in time and space:Prompt event: e+ - e- annihilation – 2 γ rays

Delayed event: 2.2 MeV

γ ray about 200 μs later.

n

e+γ

γ

γνe2.2MeV

e + p+ e+ + nEthreshold = 1.806 MeV

PromptEvent

Delayed Event

p

200 μsEprompt = E - 0.8 MeV


December, 15 2005

Event Selection CutsEvent Selection Cuts- target volume cut (R < 5.5 m)

4.61 x 1031 target protons, - inverse β decay cut

- timing correlation cut (0.5μs < ΔT < 1000μs)- vertex correlation cut (ΔR < 2.0 m)- delayed energy cut (1.8MeV < Edelay < 2.6MeV)

***Efficiency of inverse β decay cut (89.8 + 1.5)%- prompt energy analysis threshold (2.6 MeV < Eprompt< 8.5 MeV)*- cosmic ray muon spallation event cut (spallation - shattering of a nucleus by a highly energetic cosmic-ray particle)

*As a cross-check, analysis with lower energy threshold of 1.6 MeV prompt energy has been performed as well. Data sample increase 40%. However, lower energy threshold requires additional background subtraction.


December, 15 2005

Cosmic Ray Muon Spallation CutsCosmic Ray Muon Spallation Cuts

- Cosmic muon rate in KamLAND is 0.34 Hz.- 2 ms veto is applied after each tagged muon- 2 sec veto is applied after showering muon- 2 sec veto along LS muon track with 3 m radius

*** Spallation cuts introduce

around 9.7% additional dead time.


December, 15 2005

Anti-neutrino CandidatesAnti-neutrino Candidates

• From March 9th 2002 to January 11th 2004 total livetime is:

515.1 days• After applying selection cuts,

the number of selected anti-neutrino candidates is:

258 events (Eprompt>2.6MeV)

or

362 events (Eprompt>1.6MeV)


December, 15 2005

Estimated Systematic Uncertainties

Estimated Systematic Uncertainties

• Target volume 4.7%• Energy threshold 2.3%• Efficiency of cuts 1.6%• Livetime 0.06%• Reactor power 2.1%• Fuel composition 1.0%• Anti-neutrino spectra 2.5%• Anti neutrino cross-section 0.2%• Total 6.5%

The largest contribution


December, 15 2005

Analysis BackgroundsAnalysis Backgrounds

- Geo-neutrinos coming from

the radioactive decay chains

of 238U and 232Th negligible (14 + 5)

- Accidental backgrounds (2.69 + 0.05) (10.73 + 0.04)

- 9Li/8He Background (4.8 + 0.9) (6.2 + 1.0)

- 13C(,n)16O background (10.3 + 7.1) (13.5 + 10.8)

- Total (17.73 +8.05) (44.43 + 16.84)

E > 3.4 MeV E > 2.4 MeV


December, 15 2005

Anti-neutrino Flux at

KamLAND

Anti-neutrino Flux at

KamLAND


December, 15 2005

Anti-neutrino Flux from Man-made ReactorsAnti-neutrino Flux from Man-made Reactors

- 79% is within range 138-214km

- ave. dist. 180 km- Expected number of

events in 515.1 days of livetime:

365 + 23.7 (syst)

493.2 + 32.0 (syst.)

in the unoscillated case.

E > 3.4 MeV

E > 2.4 MeV


December, 15 2005

Anti-neutrino Spectrum from Geo-reactorAnti-neutrino Spectrum from Geo-reactor

• Reactor spectrum for the deep Earth reactor is assumed to be a typical commercial reactor spectrum.

• It is assumed that its output is very stable (on the data taking scale) 0.0102 events/TW·day

0.0137 events/TW·day

E > 2.4 MeV


December, 15 2005

AnalysisAnalysis


December, 15 2005

Detecting a Geo-reactorDetecting a Geo-reactor

• Geo-reactor signal - 0 to 14% (10 TW) of the signal at KamLAND.

• KamLAND can detect signature spectrum from

geo-reactor, as a constant νe flux on the top of varying νe flux from terrestrial reactors.

- Upper limit on the geo-reactor thermal power set using statistical approach: Maximum Likelihood Method*.

*Maximum likelihood estimation (MLE) is a popular statistical method used to make inferences about parameters of the underlying probability distribution of a given data set.


December, 15 2005

Analysis OutlineAnalysis Outline

• The analysis is based on 776 ton-year exposure of KamLAND to neutrinos.

• Geo-reactor power is treated as a completely free parameter

• Analysis consists of 2 parts:– Rate + Spectrum shape analysis using global solar

solution for oscillation parameters (independent of KamLAND) for E > 3.4 MeV.

– Cross-check analysis with lower energy threshold

E > 2.4 MeV


December, 15 2005

Two Different Choices for Global Solar Oscillation Parameters

Two Different Choices for Global Solar Oscillation Parameters

• Two different sets of oscillation parameters used.• Effects on the geo-reactor power output results tested.

SNO old

2003

SNO new

2005

m2 = 6.45 ·10-5 eV2

sin2 2 = 0.82

m2 = 6.5 ·10-5 eV2

sin2 2 = 0.86


December, 15 2005

Time dependent survival probabilityTime dependent survival probability

Survival probability changes daily due to the distance flux variation (reactors being turned off etc.).

Also energy spectrum is time dependent.

Difference in shapedue to the difference inoscillation parameters.


December, 15 2005

Choice of Maximum Likelihood Function

Choice of Maximum Likelihood Function

• Analysis takes into account both daily rate and spectrum shape information with flux time variation included.

• Variable parameters in the fit are:– Geo-reactor rate (free)

– Detection efficiency (constrained)

– 9Li muon spallation background (constrained)

– 13C(α,n)16O background (constrained)

– Δ m2 (constrained)

– sin2 2θ (constrained)*Geoneutrino background from terrestrial uranium is also treated as a fit parameter in the lower energy cross-check analysis.

} BG

}OP


December, 15 2005

Analysis ResultsAnalysis ResultsGeo-reactor power < 19 TW at 90% C.L.

16 geo-reactor events in the data sample


December, 15 2005

Energy Spectrum for the Best Fit Result

Energy Spectrum for the Best Fit Result

Observed spectrum is time integrated, while the best fit is obtained from the time varying maximum likelihood function best fit.


December, 15 2005

The Δχ2 Test as a Function of Geo-reactor Power

The Δχ2 Test as a Function of Geo-reactor Power

The best fit with SNO old (2003) choice of mixing parameters

Very wide minimumVery wide minimum


December, 15 2005

Summary and ConclusionSummary and Conclusion


December, 15 2005

Comparison of the Best Fit Result with Geological Data

Comparison of the Best Fit Result with Geological Data

19-31 TW

31-44 TW

0-12 TW


December, 15 2005

ConclusionConclusion• Upper limit on the power of the geo-reactor have been set Upper limit on the power of the geo-reactor have been set

for the first time.for the first time.• The best fit is: The best fit is:

• UpperUpper limit on geo-reactor power is 19 TW at 90% C.L. limit on geo-reactor power is 19 TW at 90% C.L.• Final result greatly influenced by the input oscillation

parameters. • KamLAND size detector far away from nuclear reactors

needed for high confidence (>99.99%) measurement. • Hawaii presents an excellent choice for a definite

geo-reactor measurement (Hanohano).


December, 15 2005


December, 15 2005

The Existence of Geo-reactor …The Existence of Geo-reactor …

…can explain the following unresolved question:

- provide the energy source for driving the Earth’s magnetic field (0.02-10 TW of power running for more than 3 billion years!!!).

- easily explains reversals of the geo-magnetic field

(171 reversals recorded in the last 70 million years).

- provide explanation for the up to 40 times higher measured ratios (comparing to average atmospheric ratio) of 3He/4He observed in volcanic plumes in Hawaii, Iceland some other places.


December, 15 2005

Earth ModelsEarth ModelsTraditional Model (BSE): content of the inner core based on carbonaceous, chondrites. As a result, U and Th are in the form of oxides, act as lithophiles and can exist in the crust and mantle only.

Nuclear Earth Model (by M. Herndon): content of the inner core based on rare enstatite chondrites. U and Th are alloyed with Fe or S, act as siderophiles and due to high density can exist in the inner core and particularly the Earth’s center.


December, 15 2005

Geo-reactor Sustainability Geo-reactor Sustainability

- 4.5 billion years ago,235U/238U ratio was high enough for the nuclear fission reaction to occur.

- Fast breeder nuclear reactor was simulated using the SCALE code package (by M. Herndon) and shown feasibility and sustainability for 4.5 billion years.

235U/238U > 5%

Fission products must be removed


December, 15 2005

Geo-reactor and 3He/4He anomalyGeo-reactor and 3He/4He anomaly

• SCALE code package was used (by M. Herndon) to estimate tritium production, since tritium decays into 3He with 12 years lifetime.

• Estimated ratios resemble observations from vents in Hawaii, Iceland and MORBs.


December, 15 2005

Has Natural Nuclear Reactor Ever Been Observed?

Has Natural Nuclear Reactor Ever Been Observed?

• YES!… Natural nuclear reactor has already been seen in nature.And not just one, but 17 of them were found. Although, these reactors came to be, by a different process, they operated 2 billion years ago, for about a million years in total, as fast breeder reactors. They were discovered in Oklo uranium mine in Gabon, Africa in 1972.

2 billion years ago, natural nuclear reaction could occur, due to the larger percentage of 235U (~3%)


December, 15 2005

Rate TermRate Term

• Rate term is described by Poisson distribution

Ndays is a number of days in the chosen data set

μi = Eff · Lti · (P0 ·R0 + P1i ·Ri )+ (Lti /TotalLt)·(Nli + NC + Nacc)

P0 is geo-reactor survival probability

R0 is geo-reactor expected daily rate

P1 is terrestrial reactors survival probability dependent on mixing parameters and distribution of reactor flux

Ri is terrestrial reactors expected daily rate

Nli, NC and Nacc are total Li, carbon and accidental background in the data sample


December, 15 2005

Shape TermShape Term

• In the unbinned analysis, at each event’s energy contributions are added according to their spectral shape.

• The geo-reactor spectrum looks like unoscillated spectrum.

In the binned analysis, events are divided into 0.1 MeV energy bins. Each bin is described by Poisson distribution.


December, 15 2005

Constraints TermConstraints Term

• Gaussian distribution is used to constrain efficiency and mixing parameters.

• Gaussian distribution is used to constrain backgrounds.

Binned

Unbinned


December, 15 2005

The Δχ2 Test as a Function of Geo-reactor Power and Δm2

The Δχ2 Test as a Function of Geo-reactor Power and Δm2

R0[TW]

log10 Δm2 [eV2]

Δm2 region favored by KamLAND data

Δm2 region favored by KamLAND data

Δm2 region favored by solar data


December, 15 2005

The Δχ2 Test as a Function of Geo-reactor Power and sin22θThe Δχ2 Test as a Function of Geo-reactor Power and sin22θ

R0[TW]

sin2 2θ

Wide valley for sin22θ!Wide valley for sin22θ!


December, 15 2005

Unbinned Rate+Shape AnalysisUnbinned Rate+Shape Analysis• Contributions of Rate, Shape and Constraint

Likelihood Terms for the Constrained Rate+Shape Unbinned Analysis

SK I SNO SK II

Rate RateRate

Shape ShapeShape

Constr ConstrConstr

Shape termthe most constraining!

Shape termthe most constraining!


December, 15 2005

Unbinned Rate+Shape Analysis

Unbinned Rate+Shape Analysis

R0 = 6.9 TW R0 = 4.9 TWR0 = 5.9 TWR90% = 20.7 TW R90% = 18.2 TWR90% = 18.2 TW

The best fit around 6 TW90% C.L. around 19 TW

The best fit around 6 TW90% C.L. around 19 TW

The best fit moves toward larger Δm2 favored by KamLAND data

Documents

Experimental Status of Geo-reactor Search with KamLAND Detector Jelena Maričić University of Hawaii at Manoa