Transcript Geo-neutrino: Experiments

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BNO
Geo-neutrino: Experiments
Jelena Maricic
Drexel University
Neutrino Champagne – LowNu2009
October 20, 2009
Outline
• Geological motivation for geo-neutrinos
• Experimental detection of geo-neutrinos and search for georeactor with KamLAND detector
•
Prospects for precision measurement of geo-neutrino flux
and geo-reactor discovery with current and planned
experiments
• Further developments of detection techniques
• Summary
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Geologists agree! We know more about the Sun than about Earth under
our feet
GEOLOGICAL MOTIVATION FOR
GEO-NEUTRINOS
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What and How We Learn About Earth
Interior?
•
Chemical composition:
– Depth up to 670 km studied directly: melts or
drilling (12km).
– Deep Earth inaccessible. Guess composition by
abundances in meteorites and sun.
(670-6400km)
•
Density profile:
– Sound velocities from seismic data
– Total mass and moments: infer density profile
– Does not resolve chemical composition!
•
Geodynamics:
– Continental drift energized by internal heat flow
– Geomagnetic field attributed to the dynamo
effect of the core
– Energy source that powers the dynamo not
understood!
•
Heat flow:
– 43-49 TW. Not well constrained due to model
dependence (maybe 30-32 TW ?!?)
– 17-23 TW are from radioactivity in
40K, 232Th, 238U (trace elements);
predominant heat source
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Where are Radioactive Elements
Located?
• Based on the Earth’s chemical composition model:
– U/Th expected mostly in the crust and mantle
– More U/Th expected in the crust than mantle
– No U/Th expected in the core, but deep Earth is highly
inaccessible. If it is there, does it burn, breed?
 deep-core fission reactor proposed by M. Herndon as
energy source driving geodynamo – radical hypothesis
Deep core
fission reactor?
• K seems to be under-abundant on Earth:
– Some models suggest that it is accumulated in the core
U, Th, K?
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Direct Measurement of U/Th Content
with Geoneutrinos
-
Inv.  reaction:
Antineutrinos (geo-neutrinos) are
emitted in the decay chains of
40K, 232Th, 238U
e p+  e+ + n
Inv.  does
not work
for 40K!
- Low energy < 3.4 MeV; 232Th
neutrinos have lower end point
Only good for
238U neutrinos
than
detection of
- Can engage in inverse β-decay
neutrinos with
reaction
energies > 1.8 MeV.
- Only U and Th geo-neutrinos
can be detected this way
-
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From the measurement of
geo-neutrino flux,
inferences about U/Th
content of the entire
Earth can be made!
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Geo-neutrinos vs. Conventional Geological
Tools in Surveying Earth Interior?
Conventional geology uses indirect methods to learn about the Earth’s composition:
- replicated
in the laboratory
Geo-neutrinos
 direct evidence for understanding:
- only the very outside surface layers can be directly sampled
- a lot of educated guessing must be invoked to fill in
- Earth energy budget (heat flow)
gaps in the story of Earth’s evolution
- Plate
- meteorite
datatectonics (driving mechanism)
Energyasource
geodynamo
(geomagnetism)
Geo-neutrinos -provide
direct of
method
– instantaneous
information about full
- Chemical
composition
radioactive heat
production
from 232Th and 238U from ENTIRE Earth.
238U fluxes provide evidence about the amounts and distribution
- 232Th and
- Planet
formation
(crust, mantle, or even core) of 238U and 232Th
- unique input in geochemistry and geodynamics.
Existence of geo-reactor neutrinos would provide direct evidence about
geo-reactor existence and viable explanation for the energy source of the
geomagnetic field + radical change
in planetary chemistry and evolution.
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How even crude measurement is very exciting
EXPERIMENTAL DETECTION OF GEONEUTRINOS AND SEARCH FOR GEOREACTOR WITH KAMLAND
EXPERIMENT
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KamLAND:
reactor
vs.
geo-neutrinos
Geoneutrinos
Reactor Background
with oscillation
γ
γ
νe
p
Prompt
Event
e+
n
p
γ
2.2MeV
200 μs Delayed Event
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• KamLAND – 1 kton
scintillator detector
• Detects electron
anti-neutrinos via
inverse beta decay
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Crust vs. Mantle Geo-Neutrinos at KamLAND
S. Enomoto
Crust thickness:
- continental ~40 km
- oceanic ~8 km
KamLAND
U, Th are lithophile:
strong tendency to
leave the mantle and
stay in the crust
U, Th more abundant
in the crust
Sensitivity to mantle
neutrinos small,
due to the vicinity of
continental crust
Geological Setting
• Boundary of Continent and Ocean
• Island Arc
• Zn, Pb, limestone mine (skarn)
Sea of Japan
KamLAND
Japan
Trench
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Local vs. Global Neutrinos at KamLAND
Assuming uniform crustal composition
(no local variation)!
50% of flux within
500 km from KL.
Geoneutrinos from
the crust dominant!
KamLAND is looking at
‘Earth around Japan’,
if local variation is averaged enough
S. Enomoto
‘Earth around Japan’
Japan Island Arc
Hida Metamorphic Zone
Kamioka Mine
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Expected Neutrino Spectrum at KamLAND
Antineutrinos coming from nuclear reactors around Japan present
the largest source of bkg in KamLAND.
Geo-neutrino
analysis window
U/Th flux small
comparing to reactor
flux and bkgs.
Reactor neutrino
analysis window
Geoneutrinos + BG
Poor signal to bkg
ratio!
Total BG
Reactor
(,n)
Accidental
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Expected event rate:
U series: 14.9
Th series: 4.0
Reactor (E<3.4MeV): 80.4
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*749.14 days of livetime
Analysis Results (749.14 days livetime)
Unbinned spectrum-shape Maximum
Likelihood method used for analysis.
Confirmation
101 years after
Rutherford proposed
radioactivity as the
source of Earth’s heat
Best fit point
Incorporates
Th/U = 3.9 constraint
Geophysical model
Comparison of energy spectrum of observed
events with expectation.
Good
Agreement
+19
Observed: (25 - 18 ) events
• 90% confidence interval: 4.5 to 54.2
• 99% C.L. upper limit：70.7
• Ngeo=0 excluded at 95.3%(1.99σ)
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KamLAND
Results (2008)
Model
Data Fit
- Enlarged fiducial volume (6 m vs.
4.5 m)
- Livetime: 1491 days
- Analysis threshold: 0.9 MeV
Events
- Geonu flux from Enomoto et al.
model: 16TW U+Th total
- U&Th strongly
anti-correlated
Model
U/Th
56.6
13.1
Best fit
U/Th
25
36
Fit with3.9
ratio fixed
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73±27
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Search for Geo-reactor Neutrino
Signal at KamLAND
• Reactor anti neutrinos only - above 3.4 MeV
• The possible surplus of detected events implies that there may be another
source of antineutrinos that has not been accounted for  geo-reactor.
• With 2.5 times more data, statistics improved:
90%
68%
First results
The best fit value (66) TW
and 90% C.L. limit 19 TW
with
515 days of livetime (2005)
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New results
The best fit value (04) TW
and 90% C.L. limit 6.2 TW
with 1491 days of livetime (2008)
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KamLAND Prospects
Scintillator purification
decreased it - 1/10
or better
Reactor flux
~50% in last
2 years
• Next result – improved geo-neutrino and geo-reactor measurement (prospects –
exclude 0 geo-neutrino hypothesis and fully radiogenic heat hypothesis > 3)
• Precision measurement unlikely – can not constrain/differentiate among
different geological models
• No discovery level geo-reactor neutrino measurement (5 level)
• Low sensitivity to geo-neutrinos from the mantle (in high demand by geologists)
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BNO
What it takes for precision measurement
PROSPECTS WITH OTHER RUNNING
AND PLANNED NEUTRINO
EXPERIMENTS
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Locations for Possible Geonu Experiments
SNO+ (soon – 1 kton)
5400 mwe
DUSEL
(R&D – 300 kton)
4200 mwe
LENA(R&D – 50 kton)
Baksan(R&D)
Hanohano
(R&D – 10 kton)
4000 mwe
KamLAND
(running – 1kton)
2700 mwe
EARTH
(R&D)
Borexino
(running – 300 ton, 3700 mwe)
Color indicates U/Th neutrino flux, mostly from crust
(Fiorentini et al JHEP2004)
Geonu Crust and Mantle Signal at Various Detector
Sites
S. Enomoto
M. Chen
Hanohano Hawaii
KamLAND Japan
Canada
Geoneutrino flux determination – synergy among experiments:
-Continental (KamLAND, SNO+,
Borexino, LBNE at DUSEL, LENA, …)  geo-neutrino flux from the crust – multiple
sites crucial for reliable Earth model
-Oceanic (Hanohano)  geoneutrino flux from the mantle
Reactor Neutrino Backgrounds
Commercial nuclear reactor background
Geoneutrinos
KamLAND
Reactor
Background
with oscillation
Hawaii
Hanohano
Japan
KamLAND
Borexino experiment
• 300 ton liquid scintillator detector
(running from 2007)
• Mostly sensitive to geo-neutrinos
from the crust
• Comparable signal from crust and
reactors (Fiorentini et al JHEP2004)
• 5-7 geo-neutrinos/year; 2 years for 3
(Borexino collaboration - European Physical Journal
C 47 21 (2006) - arXiv:hep-ex/0602027)
•
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Geo-reactor signal: 5-21% of reactor
signal (1-6 TW)
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SNO+ experiment
• 1 kton liquid scintillator detector (will start
2011)
• Mostly sensitive to geo-neutrinos from the
crust
• Comparable signal from the crust and
reactors
• 28-38 events/year (Chen, M. C., 2006, Earth Moon
Planets 99, 221)
• Should measure U/Th ratio of the crust
• Geo-reactor signal: 2.7 – 16% of reactor
signal (1-6 TW)
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Hanohano
• 10 kton liquid scintillator
detector (R&D)
• Very sensitive to mantle
neutrinos
• 60 – 100 events/year (J. G. Learned
et al. – ``XII-th International Workshop on
Neutrino Telescope'', Venice, 2007)
• Should measure mantle U/Th
• 1:1 geo-reactor and man-made
reactor signal ratio
• Almost 5 C.L. even for 1 TW gr.
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LENA
• 50 kton liquid scintillator
detector (R&D)
• Mostly sensitive to crust
neutrinos
• Geo-neutrino signal dominates
over reactor signal
• Should measure U/Th ratio in
the crust
• 800-1200 events/year (K. A.
Hochmuth et al. - Astropart.Phys. 27 (2007) –
arXiv:hep-ph/0509136)
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• LS loaded with 0.1% Gd
• Geo-reactor signal: 6.2 – 37.5%
of reactor signal (1 – 6 TW) 24
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LBNE at DUSEL
• 300 kton detector (WCh maybe
loaded with Gd or LS)
• If filled with LS – very sensitive
to geo-neutrinos from the crust
• Should obtain U/Th in crust
• 4800 – 7200 events/year (scaled
from LENA)
• Sensitive to geo-reactor even in
the case of Gd loading (4.5 MeV
threshold vs. 3.4 MeV)
• Geo-reactor signal: 15 – 92.3 %
of reactor signal (1-6 TW)
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What geologists would really like to know
POTASSIUM 40
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Measuring Potassium 40 Content
• Radiogenic heat from potassium
40 estimated at 3 TW
• Potassium 40 below inverse beta
decay threshold
• Neutrino flux overwhelmed by
solar neutrinos by 2-3 orders of
magnitude
• Other low Qb and low ft elements
searched like 106Cd(see M. Chen,
Neutrino Sciences 2005) and
many others (Kobayashi et al,
Geophys. Res. Lett 18(633) 1991
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Uncovering neutrino detection in scintillation detectors
IMPROVING DETECTION
TECHNIQUE WITH DIRECTIONALITY
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Directionality of neutrino in inverse
beta decay
• Neutron remembers the direction –
useful for geo-neutrino detection
• Rejection of reactor backgrounds
• Problems: blurred due to
thermalization, poor reconstruction
and gamma diffusion
• Improvement: element with large
neutron c-s; heavy particle emission;
good vertex resolution
γ
γ
νe
• Li under study at Tohoky University
p
Prompt
Event
e+
n
p
γ
2.2MeV
200 μs Delayed Event
– Transparency
– 45% of KL light yield
– 7.59% natural abundance - possible
enrichement
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S. Enomoto
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
Summary

• Geo-neutrinos provide direct measurement of
radioactive elements and heat produced
• Geo-neutrinos are the only chemical probes of
entire planet
• KamLAND measured geo-neutrinos at 2  and
4  expected in 2 years
• Limit on geo-reactor set by KamLAND at 6.2 TW
(90% C.L.) –range of interest for core
• Borexino is operational, while SNO+ soon
• Future hopes – detectors in the ocean, very large
LS detectors, several locations, directionality ,
K40…

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