Present and future detectors for Geo-neutrinos: Borexino and

LENA

Applied Antineutrino Physics Workshop

APC, Paris, Dec. 2007

L. Oberauer, TU München

Physics Goals• BOREXINO (0.3kt, data taking since May 2007)

solar neutrinos 7Be, CNO, pep, 8B at low energiesgeo-neutrinosreactor neutrinossupernova neutrinos (~102 for 8Msol @ 10 kpc)

• LENA (50kt, proposed for CUPP, Pyhäsalmi)diffuse supernova neutrino backgroundproton decaygeo-neutrinossupernova neutrinos (~1.5 x 104 for 8Msol @ 10 kpc)solar neutrinos (7Be with 5600 / day)reactor neutrinosatmospheric neutrinoslong baseline accelerator neutrinos

Geo-neutrino detection

nepe • Q-value ~ 1.8 MeV

• E~ Ee - Q ( spectroscopy)

• suppress background via delayed coincidence method

n + p D + (2.2 MeV)

• position reconstruction => fiducial volume (suppress external background)

Prompt signal

Delayed signal (~200 s)

Target and detector medium: Liquid scintillator with free protons

Sensitivity on U, Th

Energy threshold

1st detection of Geo-neutrinos in KamLAND in 2005 (1kt liquid scintillator detector)

arbi

trar

y un

its

Expected event rates

• BOREXINO

around ~ 10 per year

• LENA

between ~ 3 x 102 and ~ 3 x 103 per year

(in Pyhäsalmi, Finland, continental crust)

this is extrapolated from KamLAND result

BOREXINO

Solar Neutrino electron scattering e e

Liquid scintillator technology (~300t):

Low energy threshold (~60 keV, ~15 Hz single event rate)

Good energy resolution (~500 pe/MeV and ~4.5% @ 1 MeV)

Online since May 16th, 2007

Borexino Collaboration

Kurchatov Institute(Russia)

Dubna JINR(Russia)

Heidelberg(Germany)

Munich(Germany)

Jagiellonian U.Cracow(Poland)

Perugia

Genova

APC Paris

MilanoPrinceton University

Virginia Tech. University

BOREXINO in the Italian Gran Sasso Underground Laboratory in the mountains of Abruzzo, Italy,

~120 km from Rome

LaboratoriNazionali del Gran Sasso LNGS

Shielding~3800 m.w.e

Borexino Detector and Plants

External Labs

BOREXINO Detector layout

Water Tank: and n shield water Č detector208 PMTs in water2100 m3

Carbon steel plates

Scintillator:270 t PC+PPO in a 150 m thick nylon vessel

Stainless Steel Sphere:2212 PMTs +

concentrators1350 m3

Nylon vessels:Inner: 4.25 mOuter: 5.50 m

Excellent shielding of external background

Increasing purity from outside to the central region

14C dominates below 200 KeV

210Po NOT in eq. with 210Pb

Mainly external s and s

Photoelectrons

Statistics of this plot: ~ 1 day

Arb

itra

ry u

nit

sEnergy Spectrum (no cuts)

Final Spectrum

210Po

1 Background for Geo-neutrino detection in BOREXINO

13C(,n)16O reaction main problem in KamLAND

Alphas from 210Po decay in the scintillator!

210Po in KamLAND: 39.5 mBq/m3 down to 8.8 mBq/m3 (after purification)

210Po in BOREXINO: 0.6 mBq/m3 and it decays (T1/2=138d)…

…because 210Bi < 0.0023 mBq/m3 !

(KamLAND 210Bi = 2.5 mBq/m3 (after purification))

Estimated 13C(,n)16O background rate for geo-neutrino detection in BOREXINO: ~ 0.2 per year (total volume) now

<< 0.1 per year (total volume) in one year from now

=> Signal/background > 10

2. Background: reactor

neutrinosFrom Raghavan et al., Phys. Rev. Lett. 80 (1998)

(no neutrino oscillations)

BOREXINO:

There are no reactors in Italy

Average distance ~ 800 km

Expected total rate above 1.8 MeV ~ 15 per year (oscillations included)

Backgrounds in LENA

• ~ 240 per year in [1.8 MeV – 3.2 MeV] from reactor neutrinos

• < 30 per year due to 210Po alpha-n reaction on 13C (Borexino purity assumed)

• ~ 1 per year due to cosmogenic background (9Li - beta-neutron cascade)

K. Hochmuth et al., Astropart.Phys. 27 (2007) 21-29

Can be statistically subtracted

Geo-neutrinos and LENA

Displacement rn - re for measurement of directionality ?

zenith angle distribution of geo-neutrino signals (rn – re+) in LENA

e.g. separartion between the „standard“ model from a 21 TW core model: only an Indication (1) after 10 years

-1 +1

Conclusions

• From BOREXINO we expect a good signal/background ratio

• If signal is ~ 10 / year or even less in the total volume, the measurement time should be at least 5 years

• In LENA we expect between 300 to 3000 events per year (“best bet” ~ 1500 / year)

• Also here a good signal/background ratio is expected