Experimental Investigation of Geologically Produced Antineutrinos with KamLAND

Experimental Investigation of Geologically Produced

Antineutrinos with KamLAND

Stanford University

Department of Physics

Kazumi Ishii

8/9/2005 SLAC seminar 2

Outline

• Geologically Produced Antineutrinos (Geoneutrinos)

• KamLAND

• Background Events

• Results


Structure of the Earth

• Seismic data splits Earth into 5 basic regions: core, mantle, oceanic crust, continental crust, and sediment.

• All these regions are solid except the outer core.

Image by: Colin Rose and Dorling Kindersley


Convection in the Earth

• The mantle convects even though it is solid. • It is responsible for the plate tectonics and earthquakes.• Oceanic crust is being renewed at mid-ocean ridges and recycled at

trenches.

Image: http://www.dstu.univ-montp2.fr/PERSO/bokelmann/convection.gif

5

Total Heat Flow from the Earth• Conductive heat flow

measured from bore-hole temperature gradient and conductivity

• Deepest bore-hole (12km) is only ~1/500 of the Earth’s radius.

• Total heat flow 44.21.0TW (87mW/m2), or 311TW (61mW/m2) according to more recent evaluation of same data despite the small quoted errors.

Image: Pollack et. al

Bore-hole Measurements

Radiogenic Heat

• 238U, 232Th and K generate 8TW, 8TW, and 3TW of radiogenic heat in the Earth

• Beta decays produce electron antineutrinos


Urey Ratio and Mantle Convection Models

• Urey ratio indicates what fraction of heat dissipated comes from radiogenic heat. Urey ratio can be defined as

• Some mantle convection models predict

Urey ratio > ~0.7.

Urey Ratio =

mantle heat productionmantle heat dissipation


Discrepancy?

• The measured total heat flow, 44 or 31TW, and the estimated radiogenic heat produced in the mantle, 13TW, gives Urey Ratio ~0.3 or ~0.5.

• Problem with– Mantle convection model?– Total heat flow measured?– Estimated amount of radiogenic heat production

rate?

• Geoneutrino can serve as a cross-check of the radiogenic heat production.

8/9/2005 9

Geoneutrino Signal

• KamLAND is only sensitive to antineutrinos above 1800keV• Geoneutrinos from K decay cannot be detected with KamLAND.

8/9/2005 10

U and Th in the EarthChondritic Meteorites

• U and Th concentrations in the Earth are based on measurement of chondritic meteorites.

• Chondritic meteorites consist of elements similar to those in the solar photosphere.

• Th/U ratio is 3.9 • Th/U ratio is known better

than the absolute concentrations.


U and Th Distributionsin the Earth

• U and Th are thought to be absent from the core and present in the mantle and crust.– The core is mainly Fe-Ni alloy.– U and Th are lithophile (rock-loving), and not

siderophile (metal-loving) elements.

• U and Th concentrations are the highest in the continental crust and continental sediment.– Mantle crystallized outward from the core-mantle

boundary.– U and Th prefer to enter a melt phase.

Reference Earth ModelConcentrations of U and Th

• Total amounts of U and Th in the Earth are estimated from the condritic meteorites.• Concentrations in the sediments and crusts are based on the samples on the surface, seismic data, and tectonic model.• Concentrations in the mantle are estimated by subtracting the amounts in the sediments and the crusts.

Geological Uncertainty

Variations in local U and Th concentrations contribute ~3% error in the total flux.

U and Th concentration variations due to various crustal types contribute ~7% error in the total flux.

• We assigned 10% for the observable geological uncertainty.• This does not include uncertainties in the total amounts or distributions of U and Th.

U concentrations


Neutrino Oscillations

• The weak interaction neutrino eigenstates may be expressed as superpositions of definite mass eigenstates

• The electron neutrino survival probability can be estimated as a two flavor oscillations:

3

1l li i

i

Uν ν=

=∑

( )2 2

2 2 1212

1.27 [eV ] [m], 1 sin 2 sin

[MeV]

m LP E L

Eνν

θ⎛ ⎞Δ

= − ⎜ ⎟⎝ ⎠

8/9/2005 15

KamLAND Neutrino Oscillation Measurement

• KamLAND saw an antineutrino disappearance and a spectral distortion.

• KamLAND result combined with solar experiments precisely measured the oscillation parameters.

sin2 2θ12 =0.82 ±0.07

Δm122 =7.9−0.5

+0.6 ×10−5eV 2

8/9/2005 16

• A survival probability due to neutrino oscillations,

for geoneutrino energy range.

The Expected Geoneutrino Flux

• The decay rate per unit mass

• The number of antineutrinos per decay chain per unit energy• The mass concentration as a function of position in the Earth

• The density as a function of position in the Earth

• Given an Earth model and neutrino oscillation parameters, the antineutrino flux per unit energy at KamLAND is given by

dΦ Eν ,rr( )

dEν=A

dn Eν( )dEν

d3rr '

arr '( )ρ

rr '( )P Eν ,|

rr −

rr '|( )

4π rr −

rr '

2V⊕∫

P Eν ,|

rr −

rr '|( ) ≈1−1

2sin2 2θ12 ≈0.59

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Reference Earth Model Flux

• Expected geoneutrino flux at KamLAND– 238U geoneutrinos: 2.34106 cm-2s-1

– 232Th geoneutrinos: 1.98 106 cm-2s-1

Expected Geoneutrino Detection Rate

• By multiplying the expected geoneutrino flux and cross-sections, detection rates for geoneutrinos from U and Th at KamLAND are– 238U geoneutrinos: 3.010-31 per target proton year– 232Th geoneutrinos: 0.8510-31 per target proton year

8/9/2005 19

Geoneutrino Map of the Earth

KamLAND

Simulated origins of geoneutrinos detectable with KamLAND using the reference Earth model


Geoneutrino References

• G. Marx, Menyhard N, Mitteilungen der Sternwarte, Budapest No. 48 (1960)

• M.A. Markov, Neutrino, Ed. "Nauka", Moscow, 1964• G. Eders, Nucl. Phys., 78 (1966) 657• G. Marx, Czech. J. of Physics B, 19 (1969) 1471• G. Marx and I. Lux, Acta Phys. Acad. Hung., 28 (1970) 63• C. Avilez et al., Phys. Rev. D23 (1981) 1116• L. Krauss et al., Nature 310 (1984) 191• J.S. Kargel and J.S. Lewis, Icarus 105 (1993) 1• R.S. Raghavan et al., Phys. Rev. Lett. 80 (1998) 635• C.G. Rothschild, M.C. Chen, F.P. Calaprice, Geophys. Rev. Lett. 25

(1998) 1083• F. Montovani et al., Phys. Rev. D69 (2004) 013001

Have Geoneutrinos Been Measured before?

Fred Reines’ neutrino detector (circa 1953)

By Gamow in 1953

Were Fred Reines Background Events from Geoneutrinos?

~30TW


Outline

• Geoneutrinos

• KamLAND


• Results


KamLAND Detector

Electronics Hut

Steel Sphere, 8.5m radius

Water Cherenkov outer detector225 20” PMT’s

1 kton liquid-scintillator

Inner detector1325 17” PMT’s554 20” PMT’s34% coverage

1km Overburden

Buffer oil

Transparent balloon, 6.5m radius


Inside the Detector


Determining Event Vertices

• Vertex determined using the photon arrival times at PMTs.• Calibrated using sources deployed down the center of the

detector.


Determining Event Energies

• The “visible” energy is calculated from the amount of photo-electrons correcting for spatial detector response.

• The “real” energy is calculated from the visible energy correcting for Cherenkov photons and scintillation light quenching.

Tracking Muons

Monte Carlo (line) and Data (+)


Detecting Antineutrinos with KamLAND

• KamLAND (Kamioka Liquid scintillator AntiNeutrino Detector)

dp

e+

0.5 MeV 2.2 MeV

np

0.5 MeV

νe

e-

• Inverse beta decay

νe + p → e+ + n

Eν ~ Te + 1.8MeV

• The positron loses its energy then annihilates with an electron.

• The neutron first thermalizes then captures a proton with a mean capture time of ~200s.

PromptDelayed


Selecting Geoneutrino Events

• Δr < 1m• 0.5μs < ΔT < 500μs• 1.7MeV < Eν,p< 3.4MeV • 1.8MeV < Ed< 2.6MeV • Veto after muons• Rp, Rd < 5m• ρd>1.2m

e+

0.5 MeV 2.2 MeV

0.5 MeV

PromptDelayed

*These cuts are different from the reactor antineutrino event selection cuts because of the excess background events for lower geoneutrino energies.


Outline

• Geoneutrinos

• KamLAND


• Results


Reactor Background Introduction

• KamLAND was designed to measure reactor antineutrinos.

• Reactor antineutrinos are the most significant background.

KamLAND

Reactor Backgroundwith oscillation

Geoneutrinos

Reactor Background Measurement• Reactor antineutrino signals are identical to

geoneutrinos except for the prompt energy spectrum.

• To calculate the reactor antineutrino interaction rate per target proton per year, we need to know the neutrino oscillation parameters, the detection cross-section (~0.2%) and each reactor’s• Location• Reactor thermal power (~2.1%)• Fuel composition (~1.0%)• Antineutrino spectrum (~2.5%)

Long-lived Reactor Background

• Fission fragments with half-lives greater than a few hours (97Zr, 132I, 93Y, 106Ru, 144Ce, 90Sr) may not have reached equilibrium.

• The reactor antineutrino spectrum is based on the measured β spectrum after ~1day exposure of 235U, 239Pu, and 241Pu to a thermal n flux.

• Long-lived isotopes occur in the core and spent fuel.

• Spent fuel is assumed to be at the reactor location.

Kopeikin et al. Physics of Atomic Nuclei 64 (2001) 849

235U fission products

239Pu fissionproducts

Fractional Increase in energy spectra

Antineutrino Energy[MeV]


13C(α,n)16O Background

• Alpha source, 210Po→206Pb+α.

• Natural abundance of 13C is 1.1%

• 13C(α,n)16O.• n loses energy

creating a prompt event, and is later captured creating a delayed event.

13C(,n)16O*

n(12C,12C*)n

np scattering


Cosmic Muon Induced Background

• Muons produce unstable isotopes and neutrons as they go through the detector.

• 9Li and 8He -decay producing n, mimicking inverse -decay signals.

• Any events after muons are vetoed.– 2ms after all muons– 2s within 3m cylinder of the muon

track– 2s whole detector for muons with

high light yield

FiducialVolume

Muon Veto


Random Coincidence Background

• There is a probability that two uncorrelated events pass the coincidence cuts.

• The random coincidence background event rates are calculated by different delayed event time window (10ms to 20s instead).


Background Event Summary

• The following is a summary of the expected numbers of background coincidence events.


Pulse Shape Discrimination

• Antineutrino prompt event is caused by e+ whereas

13C(α,n)16O prompt event is caused by n.

• These different prompt events produce different scintillation light time distributions allowing a statistical discrimination.

Neutrons

Gammas

S =n(ti )−e(ti )n(ti ) + e(ti )i

PMT hits

∑ ti

From AmBe source


Pulse Shape Discrimination Part 2

• This study assumes similarities in time distributions of positrons and gammas.

• This method yields consistent 13C(α,n)16O background event rate.

Neutrons Gammas

From AmBe source


Outline

• Geoneutrinos

• KamLAND


• Results


Data-set• From March, 2002 to October, 2004.

• 749.1±0.5 day of total live-time.

• (3.46 ± 0.17) × 1031 target protons.

• (7.09 ± 0.35) × 1031 target proton years.

• 0.687±0.007 of the total efficiency for geoneutrino detection.

• 14.8 ± 0.7 238U geoneutrinos and 3.9 ± 0.2 232Th geoneutrinos are expected.

Geoneutrino Candidate Energy Distribution

Expected total

Expected reactor

Expected total background

Expected U

(,n)

Random

Expected Th

Candidate Data


Rate Analysis

• 152 candidate events

• 127±13 expected background events.

• geoneutrinos.

• / (target proton-year) detected geoneutrino rate.

25-18+19

5.1-3.6+3.9 ×10 -31νe


Likelihood Analysis

• Uses un-binned likelihood analysis.

• Uses the expected prompt event energy distribution.

• Uses the neutrino oscillation parameters determined from results of KamLAND reactor antineutrino and solar neutrino experiments.

Log Likelihood Equation

logL =−N−N( )

2

2 N +σN2( )+ log

i=1

N

∑ 1N

dN E i( )dEν

⎛

⎝⎜

⎞

⎠⎟−

p −1( )2

2σ p2−

q −1( )2

2σq2−χ 2 Δm12

2 ,sin2 2θ12( )2

• : Number of candidate events observed

• : Number of candidate events expected

• : (,n) background energy scaling factor

• : (,n) background rate scaling factor

N N

q

p

dN Eν( )dEν

=NU

dPU Eν( )dEν

+NTh

dPTh Eν( )dEν

+dNr Eν ;Δm12

2 ,sin2 2θ12( )dEν

+ pdN Eν / q( )

dEν

+dNk Eν( )

dEνk

otherBG

∑

For given NU and NTh, log L is maximized by varying the other parameters.


How Many Geoneutrinos Did We See?

Expected resultfrom reference Earth model

Expected ratio from chondritic meteorites

Best fit3 U geoneutrinos18 Th geoneutrinos


How Many Geoneutrinos Did We See, Part 2?

Expected resultfrom reference Earth model

Central Value 28

Δχ2 = 2(logLmax - logL)


Reality Check…

• Could all “geoneutrinos” come from an undiscovered uranium deposit?

• Not likely

• The antineutrino flux from a 100kton uranium deposit (the world’s largest) located 1km away from KamLAND would be only 3% of expected geoneutrino flux.

Conclusions• This is the first experimental investigation of

geoneutrinos.• This is the first chemical analysis of the mantle of

the Earth.• We observed 4.5 to 54.2 geoneutrinos with 90%

C.L. • Scaling concentrations in all regions of our

reference Earth model, the 99% upper limit on geoneutrino rate corresponds to radiogenic power from U and Th decays of less than 60TW.

• The measurement is consistent with the current geological models.

Future of Geoneutrino Measurement with KamLAND

• The reactor background is irreducible for KamLAND.

• We are working on purifying the liquid scintillator, which will reduce the (,n) background events.

• More accurate (,n) cross section can lower the error on the (,n) background rate.– S. Harissopulos et al. submitted to Phys. Rev. C calculated

new (,n) cross sections with more accuracy.– G. Fiorentini et al. arXiv:hep-ph/0508048 recalculated the

number of geoneutrinos using the above cross sections and our data. They claim that we detected geoneutrinos, ~2.5σ above 0. 31-13

+14


Future Geoneutrino Experiment Considerations

• Location and geoneutrino data purity:– No nearby nuclear reactors– On oceanic crust to probe mantle – On continental crust to probe continental crust– Needs to be shielded from cosmic muons– Low radioactive background

• People are talking about – Hawaii (oceanic crust with no reactors)– Canada, South Dakota, Australia, the Netherlands, and

South Africa (continental crust with no reactors)

• Geoneutrino Meeting in Hawaii, December 2005


Acknowledgement

• Prof. E. Ohtani (Tohoku University) and Prof. N. Sleep (Stanford University)

• Japanese Ministry of Education, Culture, Sports, Science, and Technology

• United States Department of Energy• Electric associations in Japan: Hokkaido, Tohoku,

Hokuriku, Chubu, Kansai, Chugoku, Shikoku, and Kyushu Electric Companies, Japan Atomic Power Co. and Japan Nuclear cycle Development Institute

• Kamioka Mining and Smelting Company


KamLAND CollaboratorsT. Arak i1, S. Enomoto1, K. Furuno1, Y.Ga ndo1, K. Ichimura1, H. Ikeda1, K. Inoue1, Y. Kishimoto1, M. Koga1, Y. Koseki1,

T. Maeda1, T. Mitsui1, M. Motoki1, K. Nakajima1, H. Ogawa1, M. Ogawa1, K. Owada1, J.-S. Ricol1, I. Shimizu1, J. Shirai1,

F. Suekane1, A. Suzuki1, K. Tada1, S.Takeuchi1, K. Tamae1, Y. Tsuda1, H. Watanabe1, J. Busenitz2, T. Classen2, Z. Djurcic2,

G. Keefer2, D. Leonard2, A. Piepke2, E. Yakushev2, B.E. Berger3, Y. D. Chan3, M.P. Decowski3, D.A. Dwyer3, S.J. Freedman3,

B.K. Fujikawa3, J. Goldman3, F. Gray3, K.M. Heeger3, L. Hsu3, K.T. Lesko3, K.-B. Luk3, H. Murayama3, T. O’Donnell3,

A.W.P. Poon3, H.M. Steiner3, L.A. Winslow3, C. Mauger4, R.D. McKeown4, P. Vogel4, C.E. Lane5, T. Miletic5, G. Guillian6,

J.G. Learned6, J. Maricic6, S. Matsuno6, S. Pakvasa6, G.A. Horton-Smith7, S. Dazeley8, S. Hatakeyama8, A.Rojas8, R. Svoboda8,

B.D. Dieterle9, J. Detwiler10, G. Gratta10, K. Ishii10, N. Tolich10, Y. Uchida10, M. Batygov11, W. Bugg11, Y. Efremenko11,

Y. Kamyshkov11, A. Kozlov11, Y. Nakamura11, H.J. Karwowski12, D.M. Markoff12, K. Nakamura12, R.M. Rohm12, W. Tornow12,

R. Wendell12, M.-J. Chen13, Y.-F. Wang13, and F. Piquemal14 1Research Center for Neutrino Science, Tohoku University, Sendai 980-8578, Japan 2Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487, USA 3Physics Department, University of California at Berkeley and Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA 4W. K. Kellogg Radiation Laboratory, California Institute of Technology, Pasadena, California 91125, USA 5Physics Department, Drexel University, Philadelphia, Pennsylvania 19104, USA 6Department of Physics and Astronomy, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA 7Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA 8Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA 9Physics Department, University of New Mexico, Albuquerque, New Mexico 87131, USA 10Physics Department, Stanford University, Stanford, California 94305, USA 11Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA 12Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708, USA and Physics Departments at Duke University, North Carolina State University, and the University of North Carolina at Chapel Hill 13Institute of High Energy Physics, Beijing 100039, People's Republic of China 14CEN Bordeaux-Gradignan, IN2P3-CNRS and University Bordeaux I, F-33175 Gradignan Cedex, France


Geoneutrino Results in Nature

http://www.nature.com/nature/journal/v436/n7050/full/nature03980.htmlNature 436, 499-503 (28 July 2005) | doi: 10.1038/nature03980

Experimental Investigation of Geologically Produced Antineutrinos with KamLAND

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