Results from Borexino
Davide Franco
CNRS-APC
NOW 2012
September 9-16, 2012
Davide Franco – APC CNRS – NOW2012
Detector layout and radiopurity
Water Tank:
and n shield
water Č detector
208 PMTs in water
2100 m3
Carbon steel plates
Scintillator:
270 t PC+PPO in a 150 m
thick nylon vessel
Stainless Steel Sphere:
2212 PMTs
1350 m3
Nylon vessels:
Inner: 4.25 m
Outer: 5.50 m
Davide Franco – APC CNRS – NOW2012
Detection principles and signature
Borexino detects solar via their elastic scattering off electrons in a volume ofhighly purified liquid scintillator
Mono-energetic 0.862 MeV 7Be neutrinos: main target
Mono-energetic 8B, pep, CNO and possibly pp neutrinos
Detection via scintillation light:
Very low energy threshold
Good position reconstruction
Good energy resolution
BUT…
No direction measurement
The induced events can’t bedistinguished from other eventsdue to natural radioactivity
RadioIsotope
Concentration or Flux
Name
Source
Required
Achieved
cosmic
~ 10-10
<10-10
14C
Intrinsic PC/PPO
~ 10-18
~ 10-18
238U
Dust
< 10-16 g/g
~ 2 10-17
232Th
Organometallic (?)
(in scintillator)
~ 7 10-18
210Po
Surface contam.
~ 14
85Kr
Air (nitrogen)
< 1 c/d/100 t
= 25±3
Extreme radio-purity of the scintillator is a must!
Davide Franco – APC CNRS – NOW2012
Detector Calibration
May 2007
Detector response vs position:
100 Hz 14C+222Rn in scintillator in >100positions
Quenching and energy scale:
Beta: 14C, 222Rn in scintillator
Alpha: 222Rn in scintillator
Gamma: 139Ce, 57Co, 60Co, 203Hg, 65Zn,40K, 85Sr, 54Mn
Neutron: AmBe
MC-G4Bx
Data
Pulse shape of 14C events
LY ~ 500 p.e./MeV
Ph.Y. ~ 12000 photons/MeV
Data - MC
Davide Franco – APC CNRS – NOW2012
7Be neutrino (862 keV) rate @ 4.6%Phys. Rev. Lett. 107, (2011) 141302
740 live days
MC Fit
Analytical Fit
Systematics
Davide Franco – APC CNRS – NOW2012
Implication of the 7Be measurement
No oscillation excluded @ 5.0
Assuming MSW-LMA:
f7Be= 0.97± 0.09
fpp = 1.013 +0.003 -0.010
fCNO < 1.7% (95 % C.L.)
Pee = 0.51 ± 0.07 @ 867 keV
no power to resolve low/highmetallicity problem
< 5.4 10-11 b
Neutrino magnetic moment limit:
Davide Franco – APC CNRS – NOW2012
The Day-Night Asymmetry
Adn = 0.001 ± 0.012 (stat) ± 0.007 (syst)
Adn = 0.001 ± 0.012 (stat) ± 0.007 (syst)
LOW ruledout at 8.5
LOW ruledout at 8.5
A neutrino “regeneration” isexpected only in the LOWsolution
A neutrino “regeneration” isexpected only in the LOWsolution
Davide Franco – APC CNRS – NOW2012
8B neutrinos with the lowest threshold: 3 MeV
2.6 MeV ’s from 208Tl onPMT’s and in the buffer
All volume
R < 3 m(100 tons)
Energy spectrum in Borexino
(after subtraction)
Expected 8B rate in100 tons of liquidscintillator above 2.8MeV:
0.26±0.03 c/d/100tons
> 5 distant from the 2.6 MeV peak
S/B ratio < 1/6000!!!
live-time: 246 days
Davide Franco – APC CNRS – NOW2012
8B neutrino rate measurement
raw spectrum
cut
FV cut
cosmogenic,neutron, 214Biand 10C cuts
208Tl
3.0-16.3 MeV
5.0-16.3 MeV
Rate [c/d/100 tons]
0.22±0.04±0.01
0.13±0.02± 0.01
ESexp [106 cm−2s−1]
2.4±0.4±0.1
2.7±0.4±0.2
ESexp/ESth
0.88±0.19
1.08±0.23
Davide Franco – APC CNRS – NOW2012
First observation of pep neutrinos
+ 12C → + 11C + n
+ p → d +
→11B + e+ + e
Three Fold Coincidence (TFC):
space-time veto removes 90% of 11Cpaid with 50% loss of exposure
11C ~ 30 min
Davide Franco – APC CNRS – NOW2012
o-Ps in scintillators
Measurements of the o-Psmean-life and formationprobability in scintillators withthe PALS technique
Measurements of the o-Psmean-life and formationprobability in scintillators withthe PALS technique
D. Franco, G. Consolati, D. Trezzi, Phys. Rev. C83 (2011) 015504
Pulse shape induceddistortion
Pulse shape induceddistortion
MC
~ 3 ns
p ~ 50%
Davide Franco – APC CNRS – NOW2012
Multivariate maximum likelihood fit
Energy spectral fit
Energy spectral fit
Radial fit
Radial fit
Pulse shape fit
Pulse shape fit
Pulse shape test
Pulse shape test
Davide Franco – APC CNRS – NOW2012
pep neutrinos: results
pep neutrinos:
Rate: 3.1 ± 0.6(stat) ± 0.3(sys) cpd/100 t
Assuming MSW-LMA: Φpep = 1.6 ± 0.3 108 cm-2 s-1
No oscillations excluded at 97% C.L.
Absence of pep solar ν excluded at 98%
CNO neutrinos:
only limits, correlation with 210Bi;
CNO limit obtained assuming pep @ SSM
CNO rate < 7.1 cpd/100 t (95% c.l.)
Assuming MSW-LMA:
ΦCNO < 7.7 108 cm-2 s-1 (95% C.L.)
the strongest limit to date
not sufficient to resolve metallicity problem
Δχ2 profile for fixed pep and CNO rates
Δχ2 profile for fixed pep and CNO rates
Borexino
limit
Davide Franco – APC CNRS – NOW2012
The Borexino Solar neutrino spectroscopy
Davide Franco – APC CNRS – NOW2012
Status and future perspectives
Since July 2010, purification campaigns:
• Nitrogen stripping successful in 85Kr removal:
85Kr < 8.8 cpd / 100 t (2007-2010: 31.2 ± 5)
• moderate success in 210Bi removal by water extraction:
210Bi : (16 + 4) cpd / 100 t (2007-2010: 41.0 ± 2.8)
• unprecedented 238U and 232Th radio-purity:
238U < 9.7 10-19 g/g and 232Th < 2.9 10-18 g/g
• 210Po natural decreasing:
~5 cpd / t
Borexino phase II started:
• Solar neutrino program:
- Improve 7Be, 8B → test of MSW
- Confirm pep at more than 3 σ
- Improve upper limit on CNO → probe metallicity
- Attempt direct pp measurement
• more statistics for an update of geo-neutrino measurement;
• another long-term scientific goals under discussion (sterile?)
Davide Franco – APC CNRS – NOW2012
A glance at the Borexino physics results
Neutrino speed: Measurement of CNGS muon neutrino speed with Borexino, submitted
Pep & CNO limit : First evidence of pep solar neutrinos by direct detection in Borexino, Phys.Rev. Lett. 108 (2012) 051302.
7Be ADN: Absence of day--night asymmetry of 862 keV 7Be solar neutrino rate in Borexinoand MSW oscillation parameters, Phys. Lett. B 707 (2012) 22.
7Be @ 5%: Precision measurement of the 7Be solar neutrino interaction rate in Borexino, Phys.Rev. Lett. 107 (2011) 141302.
Solar antinu limits: Study of Solar and other unknown anti-neutrino fluxes with Borexino atLNGS, Phys. Lett. B696 (2011) 191-196.
Geo-nu: Observation of Geo-Neutrinos, Phys. Lett. B687 (2010) 299-304.
8B > 3 MeV: Measurement of the solar 8B neutrino rate with a liquid scintillator target and 3MeV energy threshold in the Borexino detector, Phys. Rev. D82 (2010) 033006.
7Be @ 10%: Direct Measurement of the Be-7 Solar Neutrino Flux with 192 Days of BorexinoData, Phys. Rev. Lett. 101 (2008) 091302.
7Be @ 17%: First real time detection of Be-7 solar neutrinos by Borexino, Phys. Lett. B658 (2008) 101-108
+ muon modulation + cosmogenics + axions + Pauli principle + magnetic moment + ….
Davide Franco – APC CNRS – NOW2012
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
Davide Franco – APC CNRS – NOW2012
Backup
Davide Franco – APC CNRS – NOW2012
Geo-neutrinos: results
Null hypothesis rejected at 4.2
Null hypothesis rejected at 4.2
