present and future detectors for geo-neutrinos: borexino and lena
DESCRIPTION
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 7 Be, CNO, pep, 8 B at low energies geo-neutrinos - PowerPoint PPT PresentationTRANSCRIPT
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)
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