Transcript Results from Borexino NOW 2012 September 9-16, 2012 Davide Franco CNRS-APC Detector layout and radiopurity Stainless Steel Sphere: 2212 PMTs 1350 m3 Scintillator: 270 t PC+PPO in a 150

Results from Borexino
NOW 2012
September 9-16, 2012
Davide Franco
CNRS-APC
Detector layout and radiopurity
Stainless Steel Sphere:
2212 PMTs
1350 m3
Scintillator:
270 t PC+PPO in a 150 mm
thick nylon vessel
Water Tank:
g and n shield
m water Č detector
208 PMTs in water
2100 m3
Nylon vessels:
Inner: 4.25 m
Outer: 5.50 m
Carbon steel plates
Davide Franco – APC CNRS – NOW2012
Detection principles and n signature
 Borexino detects solar n via their elastic scattering off electrons in a volume of
highly 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 n induced events can’t be
distinguished from other b events
due to natural radioactivity
RadioIsotope
Name
Source
m
cosmic
14C
Intrinsic PC/PPO
238U
Dust
232Th
Organometallic (?)
210Po
Surface contam.
85Kr
Air (nitrogen)
Concentration or Flux
Required
Achieved
~ 10-10
<10-10
~ 10-18
~ 10-18
< 10-16 g/g
~ 2 10-17
(in scintillator)
~ 7 10-18
~ 14
< 1 c/d/100 t
= 25±3
Extreme radio-purity of the scintillator is a must!
Davide Franco – APC CNRS – NOW2012
Detector Calibration
Detector response vs position:
100 Hz 14C+222Rn in scintillator in >100
positions
MC-G4Bx
Data
Quenching and energy scale:
Beta: 14C, 222Rn in scintillator
Alpha: 222Rn in scintillator
Gamma: 139Ce, 57Co, 60Co, 203Hg, 65Zn,
40K, 85Sr, 54Mn
Neutron: AmBe
Data - MC
May 2007
Pulse shape of 14C events
LY ~ 500 p.e./MeV
Ph.Y. ~ 12000 photons/MeV
Davide Franco – APC CNRS – NOW2012
7Be
neutrino (862 keV) rate @ 4.6%
Phys. Rev. Lett. 107, (2011) 141302
740 live days
Systematics
MC Fit
Analytical Fit
Davide Franco – APC CNRS – NOW2012
Implication of the 7Be measurement
Pee = 0.51 ± 0.07 @ 867 keV
no power to resolve low/high
metallicity problem
No oscillation excluded @ 5.0 s
Assuming MSW-LMA:
Neutrino magnetic moment limit:
 f7Be= 0.97± 0.09
 fpp = 1.013 +0.003 -0.010
 fCNO < 1.7% (95 % C.L.)
Davide Franco – APC CNRS – NOW2012
mn < 5.4 10-11 mb
The Day-Night Asymmetry
A neutrino “regeneration” is
expected only in the LOW
solution
LOW ruled
out at 8.5 s
Adn = 0.001 ± 0.012 (stat) ± 0.007 (syst)
Davide Franco – APC CNRS – NOW2012
8B
neutrinos with the lowest threshold: 3 MeV
Expected 8B n rate in
100 tons of liquid
scintillator above 2.8
MeV:
2.6 MeV g’s from 208Tl on
PMT’s and in the buffer
All volume
0.26±0.03 c/d/100
tons
R<3m
(100 tons)
Energy spectrum in Borexino
(after m subtraction)
> 5s distant from the 2.6 MeV g peak
live-time: 246 days
S/B ratio < 1/6000!!!
Davide Franco – APC CNRS – NOW2012
8B
neutrino rate measurement
raw spectrum
m cut
FV cut
cosmogenic,
neutron, 214Bi
and 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
FESexp [106 cm−2s−1]
2.4±0.4±0.1
2.7±0.4±0.2
FESexp/FESth
0.88±0.19
1.08±0.23
Davide Franco – APC CNRS – NOW2012
First observation of pep neutrinos
m + 12C → m + 11C + n
11C
t ~ 30 min
+p→d+g
→11B + e+ + ne
Three Fold Coincidence (TFC):
space-time veto removes 90% of 11C
paid with 50% loss of exposure
Davide Franco – APC CNRS – NOW2012
o-Ps in scintillators
D. Franco, G. Consolati, D. Trezzi, Phys. Rev. C83 (2011) 015504
t ~ 3 ns
p ~ 50%
Measurements of the o-Ps
mean-life and formation
probability in scintillators with
the PALS technique
Pulse shape induced
distortion
MC
Davide Franco – APC CNRS – NOW2012
Multivariate maximum likelihood fit
Pulse shape test
Pulse shape fit
Davide Franco – APC CNRS – NOW2012
Energy spectral fit
Radial fit
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
Davide Franco – APC CNRS – NOW2012
Borexino
limit
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 Borexino
and 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 at
LNGS, 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 3
MeV 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 Borexino
Data, 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
Genova
Milano
Princeton University
APC Paris
Perugia
Dubna JINR
(Russia)
Kurchatov
Institute
(Russia)
Virginia Tech. University
Munich
(Germany)
Jagiellonian U.
Cracow
(Poland)
Heidelberg
(Germany)
Davide Franco – APC CNRS – NOW2012
Backup
Davide Franco – APC CNRS – NOW2012
Geo-neutrinos: results
Null hypothesis rejected at 4.2s
Davide Franco – APC CNRS – NOW2012