Present and future detectors for Geo-neutrinos: Borexino and LENA Applied Antineutrino Physics Workshop APC, Paris, Dec L. Oberauer, TU München

Physics Goals BOREXINO (0.3kt, data taking since May 2007) solar neutrinos 7 Be, CNO, pep, 8 B at low energies geo-neutrinos reactor neutrinos supernova neutrinos (~10 2 for 8M 10 kpc) LENA (50kt, proposed for CUPP, Pyhäsalmi) diffuse supernova neutrino background proton decay geo-neutrinos supernova neutrinos (~1.5 x 10 4 for 8M 10 kpc) solar neutrinos ( 7 Be with 5600 / day) reactor neutrinos atmospheric neutrinos long baseline accelerator neutrinos

Geo-neutrino detection Q-value ~ 1.8 MeV E  ~ E e - 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) arbitrary units

Expected event rates BOREXINO around ~ 10 per year LENA between ~ 3 x 10 2 and ~ 3 x 10 3 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 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 Milano Princeton University Virginia Tech. University

BOREXINO in the Italian Gran Sasso Underground Laboratory in the mountains of Abruzzo, Italy, ~120 km from Rome Laboratori Nazionali 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 detector 208 PMTs in water 2100 m 3 Carbon steel plates Scintillator: 270 t PC+PPO in a 150  m thick nylon vessel Stainless Steel Sphere: 2212 PMTs + concentrators 1350 m 3 Nylon vessels: Inner: 4.25 m Outer: 5.50 m Excellent shielding of external background Increasing purity from outside to the central region

14 C dominates below 200 KeV 210 Po NOT in eq. with 210 Pb Mainly external  s and  s Photoelectrons Statistics of this plot: ~ 1 day Arbitrary units Energy Spectrum (no cuts)

Final Spectrum 210 Po

1 Background for Geo-neutrino detection in BOREXINO 13 C( ,n) 16 O reaction main problem in KamLAND Alphas from 210 Po decay in the scintillator! 210 Po in KamLAND: 39.5 mBq/m 3 down to 8.8 mBq/m 3 (after purification) 210 Po in BOREXINO: 0.6 mBq/m 3 and it decays (T 1/2 =138d)… …because 210 Bi < mBq/m 3 ! (KamLAND 210 Bi = 2.5 mBq/m 3 (after purification))

Estimated 13 C( ,n) 16 O 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 neutrinos From 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 210 Po alpha-n reaction on 13 C (Borexino purity assumed) ~ 1 per year due to cosmogenic background ( 9 Li - beta-neutron cascade) K. Hochmuth et al., Astropart.Phys. 27 (2007) Can be statistically subtracted

Geo-neutrinos and LENA Displacement r n - r e for measurement of directionality ? zenith angle distribution of geo- neutrino signals (r n – r e+ ) in LENA e.g. separartion between the „standard“ model from a 21 TW core model: only an Indication (1  ) after 10 years +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