Transcript n - KamLAND - Stanford University

Experimental Investigation of
Geologically Produced
Antineutrinos with KamLAND
Stanford University
Department of Physics
Kazumi Ishii
Outline
• Geologically Produced Antineutrinos
(Geoneutrinos)
• KamLAND
• Background Events
• Results
8/9/2005
SLAC seminar
2
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
8/9/2005
SLAC seminar
3
Convection in the Earth
Image: http://www.dstu.univ-montp2.fr/PERSO/bokelmann/convection.gif
• 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.
8/9/2005
SLAC seminar
4
Total Heat Flow from the Earth
Bore-hole Measurements
• 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
44.21.0TW (87mW/m2),
or 311TW (61mW/m2)
according to more recent
evaluation of same data
despite the small quoted
errors.
5
Image: Pollack et. al
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
mantle heat production
Urey Ratio 
mantle heat dissipation
• Some mantle convection models predict
Urey ratio > ~0.7.
8/9/2005
SLAC seminar
7
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
SLAC seminar
8
Geoneutrino Signal
• KamLAND is only sensitive to antineutrinos above 1800keV
• Geoneutrinos from K decay cannot be detected with KamLAND.
8/9/2005
9
U and Th in the Earth
Chondritic 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.
8/9/2005
10
U and Th Distributions
in 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.
8/9/2005
SLAC seminar
11
Reference Earth Model
Concentrations 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.
Sediment
Continental Crust
Oceanic Crust
Mantle
Core
Continental
Oceanic
Upper
Middle
Lower
U [ppm]
2.8
1.68
2.8
1.6
0.2
0.1
0.012
0
Th [ppm]
10.7
6.91
10.7
6.1
1.2
0.22
0.048
0
Geological Uncertainty
• 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
U and Th concentration variations due to
various crustal types contribute ~7% error in
the total flux.
Variations in local U and Th
concentrations contribute ~3% error
in the total flux.
Neutrino Oscillations
• The weak interaction neutrino eigenstates may
be expressed as superpositions of definite mass
eigenstates
3
 l   U li  i
i 1
• The electron neutrino survival probability can be
estimated as a two flavor oscillations:
 1.27m122 [eV2 ]L[m] 
P  E , L   1  sin 212 sin 

E
[MeV]



2
8/9/2005
2
SLAC seminar
14
KamLAND Neutrino Oscillation
Measurement
• KamLAND saw an antineutrino disappearance and a
spectral distortion.
• KamLAND result combined with solar experiments
precisely measured the oscillation parameters.
2
0.6
5
2
2
m

7.9

10
eV
sin 212  0.82  0.07
12
0.5
8/9/2005
15
The Expected Geoneutrino Flux
• Given an Earth model and neutrino oscillation parameters, the
antineutrino flux per unit energy at KamLAND is given by

d E ,r
dE
  A dn E 

dE

V
3
d r'


a r '  r ' P E ,| r  r ' |
4 r  r '
2
• 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
• A survival probability due to neutrino oscillations,
r r
P E ,| r  r ' | 1 12 sin 2 212  0.59 for geoneutrino energy range.
8/9/2005
16
Reference Earth Model Flux
• Expected geoneutrino flux at KamLAND
–
–
8/9/2005
238U
geoneutrinos: 2.34106 cm-2s-1
232Th geoneutrinos: 1.98 106 cm-2s-1
17
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: 3.010-31 per target proton year
232Th geoneutrinos: 0.8510-31 per target proton year
Geoneutrino Map of the Earth
Simulated origins of geoneutrinos detectable with KamLAND
using the reference Earth model
KamLAND
8/9/2005
19
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
8/9/2005
SLAC seminar
20
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
Background Events
Results
8/9/2005
SLAC seminar
23
1km Overburden
KamLAND
Detector
Electronics Hut
Steel Sphere, 8.5m radius
Inner detector
1325 17” PMT’s
554 20” PMT’s
34% coverage
1 kton liquidscintillator
Transparent balloon, 6.5m radius
Buffer oil
Water Cherenkov outer detector
225 20” PMT’s
8/9/2005
SLAC seminar
24
Inside the Detector
8/9/2005
SLAC seminar
25
Determining Event Vertices
• Vertex determined using the photon arrival times at PMTs.
• Calibrated using sources deployed down the center of the
detector.
8/9/2005
SLAC seminar
26
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.
8/9/2005
SLAC seminar
27
Tracking Muons
Monte Carlo (line) and Data (+)
Detecting Antineutrinos with
KamLAND
Delayed
• KamLAND (Kamioka
Liquid scintillator
AntiNeutrino Detector)
• Inverse beta decay
e + p → e+ + n
E ~ Te + 1.8MeV
Prompt
0.5 MeV 
e
0.5 MeV 
2.2 MeV
e+ n
p
p
d
e
• The positron loses its energy then annihilates
with an electron.
• The neutron first thermalizes then captures a
proton with a mean capture time of ~200ms.
8/9/2005
SLAC seminar
29

Selecting Geoneutrino Events
Delayed
Prompt
0.5 MeV
0.5 MeV

2.2 MeV

e+

•
•
•
•
•
•
•
Δr < 1m
0.5μs < ΔT < 500μs
1.7MeV < E,p< 3.4MeV
1.8MeV < Ed< 2.6MeV
Veto after muons
Rp, Rd < 5m
ρd>1.2m
*These cuts are different from the reactor antineutrino event selection cuts
because of the excess background events for lower geoneutrino energies.
8/9/2005
SLAC seminar
30
Outline
•
•
•
•
Geoneutrinos
KamLAND
Background Events
Results
8/9/2005
SLAC seminar
31
Reactor Background Introduction
Geoneutrinos
KamLAND
Reactor Background
with oscillation
• KamLAND was designed to measure reactor
antineutrinos.
• Reactor antineutrinos are the most significant
background.
8/9/2005
SLAC seminar
32
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
Fractional Increase in energy spectra
235U
fission
products
239Pu
fission
products
Antineutrino Energy[MeV]
Kopeikin et al. Physics of Atomic Nuclei 64 (2001) 849
• 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.
13C(α,n)16O
Background
np scattering
13C(a,n)16O*
n(12C,12C*)n
8/9/2005
SLAC seminar
• 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.
35
Cosmic Muon Induced
Background
Muon Veto
Fiducial
Volume
• 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
8/9/2005
SLAC seminar
36
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).
8/9/2005
SLAC seminar
37
Background Event Summary
• The following is a summary of the expected
numbers of background coincidence events.
Background Source
Reactor
Short-lived isotope
Long-lived Isotope
LS Radioactivity (a,n)
Random Coincidence
Spontaneous Fissions
Cascade Decays
(,n)
Muon Induced Spallation Products
Fast Neutrons
Neutrons
Total
8/9/2005
SLAC seminar
Events
80.4
1.91
42
2.38
< 0.1
negligible
negligible
0.30
< 0.1
negligible
127.0
Error
7.2
0.24
11
0.01
0.05
13.1
38
Pulse Shape Discrimination
From AmBe source
Neutrons
Gammas
PMT hits
S

i
8/9/2005
n(ti )  e(ti )
ti
n(ti )  e(ti )
• 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.
SLAC seminar
39
Pulse Shape Discrimination Part
2
From AmBe source
Neutrons
8/9/2005
Gammas
• This study assumes
similarities in time
distributions of
positrons and
gammas.
• This method yields
consistent 13C(α,n)16O
background event
rate.
SLAC seminar
40
Outline
•
•
•
•
Geoneutrinos
KamLAND
Background Events
Results
8/9/2005
SLAC seminar
41
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.
8/9/2005
SLAC seminar
42
Geoneutrino Candidate Energy
Distribution
Expected total
Candidate
Data
Expected total
background
Expected
reactor
(a,n)
Random
Expected Th
Expected U
Rate Analysis
•
•
•
•
152 candidate events
127±13 expected background events.
+19
25-18 geoneutrinos.
+3.9
-31
5.1-3.6  10 e / (target proton-year)
detected geoneutrino rate.
8/9/2005
SLAC seminar
44
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.
8/9/2005
SLAC seminar
45
Log Likelihood Equation
logL  
 
2 N   
NN
2
N
  N
dN E
dE
2
U
  N
dPU E
dE
  
 


2
 1 dN Ei 
 2 m12
,sin2 212
pa  1
qa  1
  log 



2
2
dE
2
N
2

2

i 1



p
q
N
Th
2
  dN E ;m
dPTh E
dE
r

2
12
,sin2 212
dE
2
 p
a

dNa E / qa
dE

other BG

k

 
dNk E
dE
•
N : Number of candidate events observed
• N : Number of candidate events expected
•
qa : (a,n) background energy scaling factor
•
pa : (a,n) background rate scaling factor
For given NU and NTh, log L is maximized by varying the other parameters.
How Many Geoneutrinos Did We
See?
Expected ratio
from
chondritic
meteorites
Best fit
3 U geoneutrinos
18 Th geoneutrinos
8/9/2005
Expected result
from reference
Earth model
SLAC seminar
47
How Many Geoneutrinos Did We
See, Part 2?
2 = 2(logLmax - logL)
Expected result
from reference
Earth model
8/9/2005
Central Value 28SLAC seminar
48
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.
8/9/2005
SLAC seminar
49
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 (a,n) background events.
• More accurate (a,n) cross section can lower the
error on the (a,n) background rate.
– S. Harissopulos et al. submitted to Phys. Rev. C calculated
new (a,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 31+14 geoneutrinos,
-13
~2.5 above 0.
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
8/9/2005
SLAC seminar
52
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
8/9/2005
SLAC seminar
53
KamLAND Collaborators
T. Arak i1, S. Enomoto 1, K. Furuno1, Y.Gando1, K. Ichim ura 1, H. Ikeda 1, K. Inoue1, Y. Kishim oto1, M. Koga 1, Y. Koseki1,
T. Maeda 1, T. Mitsui1, M. Motoki1, K. Nakajim a1, H. Ogawa 1, M. Ogawa 1, K. Owada1, J.-S. Ricol1, I. Shimi zu 1, J. Shirai1,
F. Suekane1, A. Suzuk i1, K. Tada 1, S.Takeuc hi1, K. Tamae1, Y. Tsuda 1, H. Watanabe1, J. Busenitz2, T. Classen2, Z. Djurcic2,
G. Keefer2, D. Leonard2, A. Piepke2, E. Yakushev2, B.E. Berger 3, Y.D. Chan3, M.P. Decowski3, D.A. Dwyer3, S.J. Freedman3,
B.K. Fujikawa 3, J. Goldman3, F. Gray3, K.M. Heeger 3, L. Hsu 3, K.T. Lesko3, K.-B. Luk 3, H. Murayama3, T. OΥDonnell 3,
A.W.P. Poon3, H.M. Steiner3, L.A. Winslow3, C. Mauger 4, R.D. McKeown4, P. Vogel4, C.E. Lane5, T. Mil etic5, G. Guilli an6,
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. Detwil er10, G. Gratta10, K. Ishii 10, N. Tolich10, Y. Uchida10, M. Batygov11, W. Bugg11, Y. Efremenko11,
Y. Kamyshkov11, A. Kozlov11, Y. Nakamura 11, H.J. Karwowski12, D.M. Markoff12, K. Nakamura 12, R.M. Rohm12, W. Tornow12,
R. Wendell 12, M.-J. Chen13, Y.-F. Wang13, and F. Piquemal14
1
Research Center for Neutrino Science, Tohoku University, Sendai 980-8578, Japan
2
Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487, USA
3
Physics Department, University of California at Berkeley and Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
4
W. K. Kellogg Radiation Laboratory, California Institute of Technology, Pasadena, California 91125, USA
5
Physics Department, Drexel University, Philadelphia, Pennsylvania 19104, USA
6
Department of Physics and Astronomy, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA
7
Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA
8
Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA
9
Physics Department, University of New Mexico, Albuquerque, New Mexico 87131, USA
10
Physics Department, Stanford University, Stanford, California 94305, USA
11
Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA
12
Triangle 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
13
Institute of High Energy Physics, Beijing 100039, People's Republic of China
14
CEN Bordeaux-Gradignan, IN2P3-CNRS and University Bordeaux I, F-33175 Gradignan Cedex, France
8/9/2005
SLAC seminar
54
Geoneutrino Results in Nature
Nature 436, 499-503 (28 July 2005) | doi: 10.1038/nature03980
http://www.nature.com/nature/journal/v436/n7050/full/nature03980.html
8/9/2005
SLAC seminar
55