Download Geo-neutrinos - Neutrino Champagne 2009

Neutrino Champagne
LowNu 2009
Fabio Mantovani
INFN - Ferrara
Towards a Refined Reference
Model for Geo-neutrinos
Bonadiman C., Boraso R., Coltorti M., Di Carlo G., Ferrari N., Fiorentini G., Ianni A., Mantovani F.,
Mariani S., Morsilli M., Nisi S., Ricci B., Riva A., Rusciadelli G., Tassinari R., Tomei C.
Summary
• Overview on geo-neutrinos
• Open questions about radioactivity in the Earth
arXiv:0707.3203
• The Reference Model
• A Refined Reference Model for Geo-neutrinos
• A case study: KamLAND and the Japan Arc
• A study in progress: Borexino and the
Central Italy
• Conclusions and perspectives
Geo-neutrinos: anti-neutrinos from the Earth
U, Th and 40K in the Earth release heat together with
anti-neutrinos, in a well fixed ratio:
• Earth emits (mainly) antineutrinos
whereas
Sun shines in neutrinos.
• A fraction of geo-neutrinos from U and Th (not from 40K) are
above threshold for inverse b on protons: n  p  e   n  1.8 MeV
• Different components can be distinguished due to different
energy spectra: e. g. anti-n with highest energy are from Uranium.
Probes of the Earth’s interior
• Deepest hole is about 12 km
• Samples from the crust (and the
upper portion of mantle) are available
for geochemical analysis.
• Seismology reconstructs density
profile (not composition) throughout all
Earth.
Geo-neutrinos: a new probe of Earth's interior
• They escape freely and instantaneously from Earth’s
interior.
• They bring to Earth’s surface information about the
chemical composition of the whole planet.
Araki et al., 2005, Nature
Open questions about natural
radioactivity in the Earth
1 - What is the
radiogenic contribution
to terrestrial heat
production?
4 - What is hidden in the
Earth’s core?
(geo-reactor,
40K,
…)
2 - How much
U and Th in
the crust?
5 - Is the standard
geochemical model
3 - How much U and
Th in the mantle?
(BSE) consistent
with geo-neutrino data?
The World Wide Reference Model*
Geo-n signals from U and Th over the globe have been
calculated by using:
• A 2°x2° crustal model
(Laske G. – 2001).
• For each of the 16200 tiles
density and thickness of
sediments, upper, middle
and lower crust are given.
• Values of the U and Th mass
abundance in each layer taken
as mean values of GERM data.
• Spread of GERM data used
as indication of uncertainties.
• Mantle is divided into two
spherically symmetrical reservoirs
(UM and LM).
• For UM measured abundances
were used
• For LM the abundances were
deduced from BSE mass balance
* F. Mantovani et al. – Phys. Rev. D 69 –
2004 - hep-ph/0309013
• No U and Th in the core
Geo-n: predictions of the BSE Reference Model
Signal from U+Th
[TNU]
Mantovani et al.
(2004)
Fogli et al.
(2005)
Enomoto et al.
(2005)
Pyhasalmi
51.5
49.9
52.4
Homestake
51.3
Baksan
50.8
50.7
55.0
Sudbury
50.8
47.9
50.4
Gran Sasso
40.7
40.5
43.1
Kamioka
34.5
31.6
36.5
Curacao
32.5
Hawaii
12.5
13.4
13.4
• 1 TNU = one event per 1032 free protons per year
• All calculations in agreement to the 10% level
• Different locations are sensitive to the contributions of
radioactivity from crust and from mantle
KamLAND 2002-2007 results on geo-neutrino
• In five years data ~ 630
counts in the geo-n energy
range:
~ 340 reactors antineutrinos
~ 160 fake geo-n, from 13C(a,n)
Taup 2007
~ 60 random coincidences
~ 70 Geo-neutrino events are obtained from subtraction.
Adding the “Chondiritic hypoythesis” for Th/U:
N (U+Th) = 75 ± 27
S(U+Th) = 39 ± 14 TNU*
This pioneering experiment has shown that the technique
for identifying geo-neutrinos is now available!!!
* I. Shimizu (KamLAND), TAUP 2007.
The Reference Model for Kamioka
• Our* world wide reference model
(16200 2°x2° tiles) predicts for KamLAND:
• The contribution of the 6
S = 34.8 ± 8.9 TNU
tiles near Kamioka was
found by us as:
Sreg = 17.7 TNU
The regional contribution
has to be
controlled/determined by
study of regional geology,
if one wants to extract the
global information brought
in by geo-n’s
* F. Mantovani et al. – Phys. Rev. D
69 – 2004 - hep-ph/0309013
Refining the Reference Model for KamLAND*
• Use a geochemical study of
the Japan Arc exposed upper
crust (166 samples
distinguishing 10 geological
classes)
• Use detailed (± 1 km)
measurements of Conrad and
Moho depth
• Use selected values for
abundances LC
• Build a new crustal map of
the Japan Arc (scale ¼° x ¼°)
• Consider possible effect of
the subducting plate
below Japan
* G. Fiorentini et al. – Physical Review D72 –
2005 – arXiv:hep-ph/0501111
Kamioka
• Take into account several sources
of uncertainties:
 (3s) errors on sample activity
measurements
 Finite resolution of geochemical
study
 Uncertainty from the Japan sea
crust characterization
 Uncertainty from subducting
plates below Japan
 Uncertainty of seismic
measurements
Refining the Reference Model for KamLAND
CONTRIBUTIONS
S (U) [TNU]
6 tiles
12.7
Subducting slab
2.3
Japan Sea
0.4
UNCERTAINTIES*
DS (U)
[TNU]
Subducting slab
2.1
• By adding the different
Upper-crust
discretization
1.7
Composition of the
upper-crust sample
1.0
contributions and summing in
quadrature independent
uncertainties:
Lower-crust
composition
0.8
Crustal depths
0.7
Japan Sea
0.3
*Full range or 3 sigma uncertainties
Sreg = 19.1 ± 3.8 TNU
In good agreement with the
estimate of the rough 2°x2°
calculation (17.6 TNU).
The Reference Model for Gran Sasso
• Our world wide reference model (16200 2°x2° tiles)
predicts for Borexino:
S = 40.5 ± 6.5 TNU
• The contribution of the 6
tiles near Borexino was
found by us (Ref. Mod.)
as:
Sreg = 15.5 TNU
• A 2°x2° tile centered at
Gran Sasso gives:
SCT = 12.2 TNU
Can we provide a more precise
assessment of this regional contribution?
3D model of the central tile
•
-
INPUT
Data of CROP seismic sections
Data from 38 deep oil and gas wells
•
IDENTIFY SIX RESERVOIRS
Cenozoic terrigenous units
Meso-Cenozoic Basinal Carbonate
units
Mesozoic Carbonate units
Permian and Paleozoic clastic units
Upper crust
Lower crust
•
OUTPUT
A 3D dimensional model, built
on 106 1 km3 cells
Extension of the different reservoirs in the
vertical profile
Compare the average thickness of different reservoirs…
3D model
[km]
Ref. Model
[km]
Sediments
~ 13
~ 0.5
Upper crust
~ 13
~ 10
Middle crust
/
~ 10
Lower crust
~8
~ 10.5
Ref. model
3D
model
Note the different proportions, although the total depth is practically the same.
The sedimentary cover of the central tile
• We collected representative samples of the sedimentary
cover and measured U and Th content by using ICP-MS:
Reservoir
Volume
[%]
a(U)
[ppm]*
a(Th)
[ppm]*
Density
[gr/cm3]
Mesozoic Carbonate units
74.6
0.31 ± 0.19
0.21 ± 0.19
2.5
Cenozoic terrigenous
18.0
2.28 ± 0.62
8.31 ± 2.45
2.1
Permian and Paleozoic clastic
5.4
2.44 ± 0.70
8.76 ± 2.52
2.6
Meso-Cenozoic Basinal
Carbonate
1.9
2.08 ± 1.47
1.62 ± 1.76
2.3
• By using these abundances and the 3D model, the estimated
signal from the sedimentary cover is:
SSed = ~6.2 TNU
• To be compared with that estimated in Ref. Mod.:
(remind the 0.5 km sediment layer)
* Standard deviation of measured
samples
SSed = 0.5 TNU
Reservoir in
Ref. Mod.
a(U) [ppm]
a(Th) [ppm]
Density
[gr/cm3]
Sediments
1.7
6.9
2.1 - 2.5
The crust composition of the CT
• We collected representative samples from
outcropping Adriatic Crust on Western Alps.
• We measured U and Th content by using ICP-MS
• To fix the relative amounts of acid and mafic rocks
in the UC we used seismic arguments, increasing
the fraction of mafic rock with depth (LC):
Reservoir
a(U) [ppm]
a(Th) [ppm]
Upper crust
1.54
7.89
Lower crust
0.30
3.53
• By using the 3D model, we estimates
the total signal from the crust of the central tile: SCrust = ~4.0 TNU
• To be compared with that estimated in Ref. Model:
Reservoir
a(U) [ppm]
a(Th) [ppm]
Upper Crust
2.5
9.8
Middle Crust
1.6
6.1
Lower Crust
0.6
3.7
SCrust = 11.7 TNU
The total signal from the central tile
The total geo-neutrino signal from the
central tile at Gran Sasso:
Reservoir
Signal from
Ref. Model
[TNU]
Signal from
3D model
[TNU]
Sediments
0.5
6.2
Crust
11.7
4.0
Total
12.2
~ 10.2
Note that:
• The increased contribution from the sediment is mainly
originated by different vertical profile of the reservoirs
• The adopted U and Th abundance and the reduced total
volume decrease the total signal from the crust
The rest of the regional contribution
We consider the region out of the central tile and refine the
model by using:
• Data of the main CROP seismic sections
• Depth conversion velocities of the crustal stratigraphic layers
• Detailed measurements of
Moho depth
By using the deduced U and
Th abundance, the signal
from the refined out-region is:
SOut = ~ 2.5 TNU
To be compared with that
estimated in Ref.:
SOut = 3.3 TNU
Conclusions
We can estimate the expected geoneutrinos signal at LNGS:
CONTRIBUTIONS
S [TNU]
Sediments of the 3D mod. central tile
6.2
Crust of the of the 3D mod. central tile
4.0
Rest of the region
2.5
Rest of the world
25.0
Total
~ 37.7
The signal is to be compared with
that estimated in Ref. Mod.: S = 40.5
For 80% eff. and 300 tons C9H12 fiducial
mass, we expect ~ 5.5 events/year at
LNGS.
The
is not completed
yet…
Thepicture
contributing
uncertainties…
For the regional contribution to the
signal, uncertainties arise from:
• Variations within measured
samples
• Measurement methods
(ICMS – Gamma spectroscopy)
• Mixture felsic/mafic rocks in the UC and LC
• Time-Depth conversion of velocities of the crustal layers
• Matching between the types of rocks and observed vp data
•…