Towards a Refined Reference Model for Geo-neutrinos

Towards a Refined Reference Model for Geo-neutrinos

Neutrino ChampagneLowNu 2009

Fabio MantovaniINFN - Ferrara

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.

• Overview on geo-neutrinos

• Open questions about radioactivity in the Earth

• 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

arXiv:0707.3203

SummarySummary

Geo-neutrinos: anti-neutrinos from the EarthGeo-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 on protons:

• Different components can be distinguished due to different energy spectra: e. g. anti- with highest energy are from Uranium.

p e n 1.8 MeV

Probes of the Earth’s interiorProbes 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

Open questions about natural radioactivity in the Earth

1 - What is the

radiogenic contribution

to terrestrial heat

production?

2 - How much

U and Th in

the crust?

3 - How much U and

Th in the mantle?

4 - What is hidden in the

Earth’s core?

(geo-reactor,40K, …)

5 - Is the standard

geochemical model

(BSE) consistent

with geo-neutrino data?

Next talk by

Maricic

The World Wide Reference Model*The World Wide Reference Model*

Geo- 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

• No U and Th in the core* F. Mantovani et al. – Phys. Rev. D 69 – 2004 - hep-ph/0309013

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

Geo-: predictions of the BSE Reference ModelGeo-: predictions of the BSE Reference Model

• In five years data ~ 630

counts in the geo- energy

range:

~ 340 reactors antineutrinos

~ 160 fake geo-, from 13C(,n)

~ 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*

Taup 2007

KamLAND 2002-2007 results on geo-neutrinoKamLAND 2002-2007 results on geo-neutrino

This pioneering experiment has shown that the technique

for identifying geo-neutrinos is now available!!!* I. Shimizu (KamLAND), TAUP 2007.

• The contribution of the 6

tiles near Kamioka was

found by us as:

Sreg = 17.7 TNU

• Our* world wide reference model

(16200 2°x2° tiles) predicts for KamLAND:

S = 34.8 ± 8.9 TNU

* F. Mantovani et al. – Phys. Rev. D 69 – 2004 - hep-ph/0309013

The Reference Model for KamiokaThe Reference Model for Kamioka

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-’s

• 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 platebelow Japan

• Take into account several sources of uncertainties:

(3) 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

Kamioka

* G. Fiorentini et al. – Physical Review D72 – 2005 – arXiv:hep-ph/0501111

Refining the Reference Model for KamLAND*Refining the Reference Model for KamLAND*

Refining the Reference Model for KamLANDRefining the Reference Model for KamLAND

CONTRIBUTIONS S (U) [TNU]

6 tiles 12.7

Subducting slab 2.3

Japan Sea 0.4

UNCERTAINTIES*S (U) [TNU]

Subducting slab 2.1

Upper-crust discretization

1.7

Composition of the upper-crust sample

1.0

Lower-crust composition

0.8

Crustal depths 0.7

Japan Sea 0.3

• By adding the different

contributions and summing in

quadrature independent

uncertainties:

Sreg = 19.1 ± 3.8 TNU

In good agreement with the

estimate of the rough 2°x2°

calculation (17.6 TNU).*Full range or 3 sigma uncertainties

The Reference Model for Gran SassoThe Reference Model for Gran Sasso

• The contribution of the 6

tiles near Borexino was

found by us (Ref. Mod.)

as:

• A 2°x2° tile centered at

Gran Sasso gives:

Sreg = 15.5 TNU

SCT = 12.2 TNU

Can we provide a more precise

assessment of this regional contribution?

• Our world wide reference model (16200 2°x2° tiles)

predicts for Borexino: S = 40.5 ± 6.5 TNU

• INPUT

- Data of CROP seismic sections

- Data from 38 deep oil and gas wells

• OUTPUTA 3D dimensional model, built on 106 1 km3 cells

3D model of the central tile3D model of the central tile

• IDENTIFY SIX RESERVOIRSCenozoic terrigenous unitsMeso-Cenozoic Basinal Carbonate

unitsMesozoic Carbonate unitsPermian and Paleozoic clastic unitsUpper crustLower crust

Extension of the different reservoirs in the vertical profile

Extension of the different reservoirs in the vertical profile

3D model

[km]

Ref. Model

[km]

Sediments ~ 13 ~ 0.5

Upper crust ~ 13 ~ 10

Middle crust / ~ 10

Lower crust ~ 8 ~ 10.5

Note the different proportions, although the total depth is practically the same.

Compare the average thickness of different reservoirs…

3D

model

Ref. model

• We collected representative samples of the sedimentary

cover and measured U and Th content by using ICP-MS:

ReservoirVolume

[%]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:

Reservoir in

Ref. Mod.a(U) [ppm] a(Th) [ppm]

Density

[gr/cm3]

Sediments 1.7 6.9 2.1 - 2.5

SSed = ~6.2 TNU

• To be compared with that estimated in Ref. Mod.:(remind the 0.5 km sediment layer)

SSed = 0.5 TNU

* Standard deviation of measured samples

Preliminary

The sedimentary cover of the central tileThe sedimentary cover of the central tile

• 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):

• By using the 3D model, we estimates

the total signal from the crust of the central tile:

• To be compared with that estimated in Ref. Model:

Reservoir a(U) [ppm] a(Th) [ppm]

Upper crust 1.54 7.89

Lower crust 0.30 3.53

SCrust = 11.7 TNUReservoir 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 = ~4.0 TNU

Preliminary

The crust composition of the CTThe crust composition of the CT

Preliminary

The total signal from the central tileThe total signal from the central tile

ReservoirSignal from Ref. Model

[TNU]

Signal from 3D model

[TNU]

Sediments 0.5 6.2

Crust 11.7 4.0

Total 12.2 ~ 10.2

The total geo-neutrino signal from the

central tile at Gran Sasso:

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

Preliminary

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

The rest of the regional contributionThe rest of the regional contribution

Preliminary

The signal is to be compared with

that estimated in Ref. Mod.: S = 40.5

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

For 80% eff. and 300 tons C9H12 fiducial

mass, we expect ~ 5.5 events/year at

LNGS.

We can estimate the expected geoneutrinos signal at LNGS:

Preliminary Pre

limin

ary

ConclusionsConclusions

Preliminary

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

• …

The picture is not completed yet…The picture is not completed yet…The contributing uncertainties…The contributing uncertainties…