Transcript Borexino …..bla bla bla - Istituto Nazionale di Fisica

From the solar neutrino problem to the
7Be neutrinos measurement: results and
perspectives of the Borexino detector
Lino Miramonti
Università degli Studi di Milano
and
Istituto Nazionale di Fisica Nucleare
Lino Miramonti
Baikal Summer School 20-27 July 2008
1
How the Sun shines
The core of the Sun reaches
temperatures of  15.5 million K.
At these temperatures, nuclear fusion
can occur which transforms 4
Hydrogen nuclei into 1 Helium
nucleus
1 Helium nucleus has a mass that is slightly (0.7%) smaller than the combined
mass of the 4 Hydrogen nuclei.
That “missing mass” is converted to energy to power the Sun.
Lino Miramonti
Baikal Summer School 20-27 July 2008
2
Net reaction:
4 1H  1 4He + energy
Mass of 4 H: 6.6943 x 10-27 kg
Mass of 1He: 6.6466 x 10-27 kg
Difference : 0.048 x 10-27 kg (0.7%)
Using E=mc2 each fusion releases 4.3 · 10-12 J 
26.7 MeV
The current luminosity of the Sun is 4 · 1026 Watts,
(600 million tons of Hydrogen per second is being converted to 596 million tons of Helium-4.
The remaining 4 million tons is released as energy).
Lino Miramonti
Baikal Summer School 20-27 July 2008
3
What about neutrinos?
We start from 4 protons and we end with 1 He nucleus which is composed of
2 protons and 2 neutrons.
This means that we have to transform 2 protons into 2 neutrons:
p  n  e  e

(inverse -decay)
In the inverse beta decay a proton becomes a neutron emitting a positron
and an electron neutrino e
Since neutrinos only interact with matter via the weak force, neutrinos
generated by solar fusion pass immediately out of the core and into space.
The study of solar neutrinos was conceived as a way to test the nuclear
fusion reactions at the core of the Sun.
Lino Miramonti
Baikal Summer School 20-27 July 2008
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Neutrino production in the Sun
In our star  98% of the energy is created in this reaction
The pp chain reaction
There are different steps in which energy (and neutrinos) are produced
 from:
pp
pep
Monocrhomatic ν’s
(2 bodies in the final state)
7Be
8B
hep
Lino Miramonti
Baikal Summer School 20-27 July 2008
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Neutrino production in the Sun
Beside pp chain reaction there is also the CNO cycle that become the dominant
source of energy in stars heavier than the Sun
(in the Sun the CNO cycle represents only 1-2 %)
 from:
13N
15O
17F
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Baikal Summer School 20-27 July 2008
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Neutrino production in the Sun
Neutrino energy spectrum as predicted by
the Solar Standard Model (SSM)
John Norris Bahcall
(Dec. 30, 1934 – Aug. 17, 2005)
7Be:
384 keV (10%)
862 keV (90%)
pep:
1.44 MeV
Lino Miramonti
Baikal Summer School 20-27 July 2008
7
Homestake: The first
solar neutrino detector
The first experiment built to detect solar
neutrinos was performed by Raymond
Davis, Jr. and John N. Bahcall in the
late 1960's in the Homestake mine in
South Dakota
“…..to see into the interior
of a star and thus verify
directly the hypothesis of
nuclear energy generation
in stars.”
Phys. Rev. Lett. 12, 300 (1964);
Phys. Rev. Lett. 12, 303 (1964);
Davis and Bahcall
Large tank of 615 tons of
liquid perchloroethylene
Neutrinos are detected via the reaction:
e+ 37Cl → 37Ar + e-
Eth = 814 keV
mostly 8B neutrinos
Remove and detect
37Ar
(1/2=35 days):
37Ar
+
e-

37Cl*
+ e
Homestake Solar
Neutrino Detector
Expected rate: Only 1 atom of 37Ar every six days in 615 tons C2Cl4!
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Baikal Summer School 20-27 July 2008
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≈ 5 37Ar atoms were extracted per month bubbling helium through the tank.
1 SNU (Solar Neutrino Unit) = 1 capture/sec/1036 atoms
Expected from SSM: 7.6 + 1.3 - 1.1 SNU
Detected in Homestake: 2.56 ± 0.23 SNU
The number of neutrino detected was about 1/3 lower than the
number of neutrino expected → Solar Neutrino Problem (SNP)
Lino Miramonti
Baikal Summer School 20-27 July 2008
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Possible Explanations to the SNP
•Standard Solar Model is not right
..but
bisede
Solar models have been tested independently by
helioseismology (studies of the interior of the
Sun by looking at its vibration modes), and the
standard solar model has so far passed all the
tests.
Non-standard solar models seem very unlikely.
•Homestake is wrong
New experiments (since about 1980) are of three types:
•Neutrino scattering in water (Kamiokande, SuperKamiokande)
•Radiochemical experiments (like Homestake, but probing
different energies) (SAGE, GALLEX)
•Heavy water experiment (SNO)
•Something happens to the 
Lino Miramonti
Baikal Summer School 20-27 July 2008
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Kamiokande  SuperKamiokande:Real time detection
Kamiokande large water Cherenkov
SuperKamiokande large water
Detector
Cherenkov Detector
•3000 tons of pure water
•1000 PMTs
SuperKamiokande
•50000 tons of pure water
•11200 PMTs
Reaction: Elastic Scattering on e-
  e    e 
Electrons
are
accelerated
to
speeds v > c/n
“faster than light”.
Eth = 7.5 MeV (for Kamiokande)
Eth = 5.5 MeV (for SKamiokande)
only 8B neutrinos (and hep)
Results:
Inferred flux  2 times lower than the prediction
Neutrinos come from the Sun! (Point directly to the source)
Lino Miramonti
Baikal Summer School 20-27 July 2008
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…looking for pp neutrinos …
Until the year 1990 there was no observation of the initial reaction in the
nuclear fusion chain (i.e. pp neutrinos). This changed with the installation of
the gallium experiments. Gallium as target allows neutrino interaction via
e+ 71Ga → 71Ge + e-
Eth = 233 keV
Less model-depended
2 radiochemical experiment were built in order to detect solar pp neutrinos.
GALLEX (and then GNO)
Located in the Gran Sasso laboratory
(LNGS) in Italy.
The tank contained 30 tonnes of natural
gallium in a 100 tonnes aqueous gallium
chloride solution
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Baikal Summer School 20-27 July 2008
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SAGE
Located at Baksan underground laboratory in Russia
Neutrino Observatory with 50 tons of metallic gallium
running since 1990-present
Results of Gallex/GNO and SAGE
The measured neutrino signal were smaller than predicted by the solar model ( 60%).
Calibration tests with an artificial neutrino source (51Cr) confirmed the proper
performance of the detector.
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Baikal Summer School 20-27 July 2008
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All experiments detect less neutrino than expected from the SSM !
Rate measurement
Homestake
SAGE
Gallex+GNO
Super-K
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Reaction
e + 37Cl  37Ar + e
e + 71Ga  71Ge + e
e + 71Ga  71Ge + e
x + e  x + e
Baikal Summer School 20-27 July 2008
Obs / Theory
0.34  0.03
0.59  0.06
0.58  0.05
0.46  0.02
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…… something happens to the  !
Standard Model assumes that neutrinos are massless
Let us assume that neutrinos have (different) masses - Δm2
Let us assume that the mass eigenstates (in which neutrinos are created and
detected)  flavor eigenstates:
e, m,  are not mass eigenstates
Mass eigenstates are 1, 2, 3
We can write:
In the simple
case of 2 
Being:
 νμ   cosθ
 
 ν    sinθ
 e 
sinθ  ν1 
 
cosθ  ν 2 
θ analogous to the Cabibbo
angle in case of quarks
νi t   νi 0eiEi t
Consider θ = 45°
m
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Baikal Summer School 20-27 July 2008
e
m
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In general this leads to the disappearance of the original neutrino flavour
2

m
P( e   m )  sin 2 2 sin 2
L
4E
Losc
4E

m 2
with the corresponding appearance of the “wrong” neutrino flavour
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Baikal Summer School 20-27 July 2008
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Three-flavor mixing
νe , νμ , ν - flavor eigenstates
ν1 , ν2 , ν3 - mass eigenstates with masses
m1, m2, m3
U is the Pontecorvo-Maki-Nakagawa-Sakata
matrix
(the analog of the CKM matrix in the hadronic sector of
the Standard Model).
3 angles: θ12 , θ13 , θ23
1 CP-violating Dirac phase: δ
2 CP-violating Majorana phases: α1 , α2
(physical only if ν’s are Majorana fermions)
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Baikal Summer School 20-27 July 2008
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The Mikheyev Smirnov Wolfenstein Effect (MSW)
… or Matter Effect
Neutrino oscillations can be enhanced by traveling through matter
The neutrino “index of refraction” depends on its scattering amplitude with matter:
The Sun is made of up/down quarks and electrons
 e, m, . All neutrinos can interact through NC equally.
  e,
Only electron neutrino can interact through CC scattering:
  e    e 
The “index of refraction” seen by e is different than the one seen by m and  .
The MSW effect gives for the probability of an electron neutrino produced at t=0
sin 2 2
to be detected as a muon neutrino:
2
P( e   m )  sin 2 2 m sin 2 (
Lino Miramonti
xW
)
osc
sin 2 m 
W2
W 2  sin 2 2  ( D  cos 2 2 ) 2
2E
D  2GF N e 2
m
Baikal Summer School 20-27 July 2008
Ne being the
electron density.
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Sudbury Neutrino Observatory
1000 tonnes D2O (Heavy Water)
12 m diameter Acrylic Vessel
18 m diameter PMT support structure
9500 PMTs
1700 tonnes inner shielding H2O
5300 tonnes outer shielding H2O
Urylon liner radon seal
depth: 6010 m.w.e. // 70 muons/day
Lino Miramonti
Baikal Summer School 20-27 July 2008
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Neutrino Reactions in SNO
ES
 x  e−   x  e−
NC
 x  d  p  n  x
- measures total 8B  flux from the Sun
- equal cross section for all  flavors
CC
e  d  p  p  e−
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Baikal Summer School 20-27 July 2008
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CC, NC FLUXES
MEASURED
INDEPENDENTLY
Best fit to data gives:
6
 2 1
 m  3.41  0.45  00..45
48 10 cm s
CC  1.68
 0.06
0.06
NC  4.94
 0.21
0.21
ES  2.35
 0.22
0.22
08
(stat.) 00..09
(syst.)
38
(stat.) 00..34
(syst.)
15
(stat.) 00..15
(syst.)
The Total Flux of Active Neutrinos is
measured independently (NC) and
agrees well with solar model
Calculations: 4.7 ± 0.5 (BPS07)
(In unitsof 106 cm2s1 )
CC
029
Pee 
 0.34  0.023(stat.) 00..031
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NC
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Baikal Summer School 20-27 July 2008
CC  
e

 NC   e   m   

ES   e  0.154( m    )
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Summary of all Solar neutrino experiments before Borexino
All experiments “see” less neutrinos than expected by SSM ……..
(but SNO in case of NC)
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Baikal Summer School 20-27 July 2008
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electron neutrinos oscillate into non-electron neutrino with these parameters:
Large mixing Angle (LMA) Region: MSW
m122  7.6 105 eV 2
sin 2 212  0.87
from S.Abe et al., KamLAND
Collab. arXiv:0803.4312v1
SOLAR only
SOLAR plus
KamLAND
Lino Miramonti
KamLAND is a detector built to
measure electron antineutrinos
coming from 53 commercial
power
reactors
(average
distance of ~180 km ).
The experiment is sensitive to
the neutrino mixing associated
with the (LMA) solution.
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The Borexino detector
at
Laboratori Nazionali del Gran Sasso
LNGS
….. a detector “to see” in real time
solar neutrinos below 1 MeV
Borexino Detector and Plants
CTF
Borexino
Lino Miramonti
Baikal Summer School 20-27 July 2008
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The Borexino solar physics goals
Radiochemical
Real time measurement
(only 0.01 %!)
Gallex/GNO
SAGE
Homestake
SNO &
SuperKamiokande
Borexino is able to
measure for the first time
neutrino coming from the
Sun in real_time with
low_energy ( 200 keV)
and high_statistic.
Eth  200 keV
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Baikal Summer School 20-27 July 2008
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7Be

pep 8B pp neutrinos
7
Be
The main goal of Borexino is the measurement of
that it will be possible:
7Be
neutrinos, thank to
• To test the Standard Solar Model and the MSW-LMA solution of the SNP
•To provide a strong constraint on the 7Be rate, at or below 5%, such as to provide an
essential input to check the balance between photon luminosity and neutrino
luminosity of the Sun
•To confirm the solar origin of 7Be neutrinos, by checking the expected 7% seasonal
variation of the signal due to the Earth’s orbital eccentricity
•To explore possible hints of non-standard neutrino-matter interactions or presence of
mass varying neutrinos.



pep
Additional Possibilities:
pep neutrinos (indirect constraint on pp neutrino flux)
8
B
8B
neutrinos with a low energy threshold
Tail end of pp neutrinos spectrum?
pp
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Baikal Summer School 20-27 July 2008
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Solar Model Chemical
Controversy
•One fundamental input of the Standard Solar Model is the metallicity
(abundance of all elements above Helium) of the Sun
 CNO
•The Standard Solar Model, based on the old metallicity [GS98] is in
agreement within 0.5% with helioseismology (measured solar sound speed).
•Recent work [AGS05] indicates a lower metallicity. → This result destroys the
agreement with helioseismology
•A lower metallicity implies a variation in the neutrino flux (reduction of  40%
for CNO neutrino flux) → A direct measurement of the CNO neutrinos rate
could help to solve this controversy
Φ
(cm-2s-1)
pp
(1010)
7Be
8B
13N
15O
17F
(109)
(106)
(108)
(108)
(106)
BS05
GS98
5.99
4.84
5.69
3.07
2.33
5.84
BS05
AGS05
6.05
4.34
4.51
2.01
1.45
3.25
Difference
+1%
-10%
-21%
-35%
-38%
-44%
Lino Miramonti
Baikal Summer School 20-27 July 2008
A direct measurement of
the CNO neutrinos rate
(never measured up to
now) could give a direct
indication of metallicity
in the core of the Sun
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The Borexino neutrino physics goals
Resonant Oscillations in Matter:
the MSW effect
For high energy neutrinos flavor change is
dominated by matter oscillations
For low energy neutrinos flavor change is
dominated by vacuum oscillations
Regime transition expected between 1-2 MeV
•Test the fundamental prediction of MSW-LMA
theory
• Exploring the vacuum-matter transition.
• Check the mass varying neutrino model
pep and 7Be neutrinos good sources to study the
transition!
Limit on the neutrino magnetic moment by analyzing the 7Be energy spectrum
and with artificial neutrino 51Cr source (MCi)
Geoneutrinos and Neutrinos from Supernovae
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Baikal Summer School 20-27 July 2008
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Detection principles and  signature
elastic scattering (ES) on electrons in very high purity liquid scintillator
  e    e 
Detection via scintillation light:
 Very low energy threshold
 Good position reconstruction
 Good energy resolution
pp
7Be
But…
pep+CNO
8B
 No direction measurement
 The  induced events can’t be distinguished from other γ/β events
due to natural radioactivity
Extreme radiopurity of the scintillator is a must!
Lino Miramonti
Baikal Summer School 20-27 July 2008
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Core of the detector: 300 tons of liquid
scintillator (PC+PPO) contained in a nylon
vessel of 8.5 m diameter. The thickness of
nylon is 125 µm.
1st shield: 1000 tons of ultra-pure buffer
liquid (PC+DMP) contained in a stainless
steel sphere of 13.7 m diameter (SSS).
2200 photomultiplier tubes pointing towards
the center to view the light emitted by the
scintillator.
2nd shield: 2400 tons of ultra-pure water
contained in a cylindrical dome.
200 photomultiplier tubes mounted on the
SSS pointing outwards to detect Cerenkov
light emitted in the water by muons.
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Baikal Summer School 20-27 July 2008
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How many 7Be neutrinos we expect?
7Be
flux on earth:   5·109 cm-2 s-1
Cross-section:
Recoil nuclear energy of the e-
 = 3.310-45 cm2
Neutrino signal:  45 events/day/100 tons above threshold (between 250-800 keV)
Including oscillations:  30 events/day/100 tons! (between 250-800 keV)
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Baikal Summer School 20-27 July 2008
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How much background we can tolerate?
Use 238U and 232Th intrinsic contamination at 10-16 g/g
– For Th:
– For U:
4.06 x 10-4 mBq/kg  0.035 cpd/ton!
12.35 x 10-4 mBq/kg  0.107 cpd/ton!
– In [250-800] keV expected about 20 events/day/100tons with offline analysis
 S/N  30/20
In 1998 through the Borexino Counting Test
Facility (CTF) it was proved the feasibility to
reach such a low level of contamination by
purification methods
•distillation (6 stages distillation, 80 mbar, 90 °C)
•water extraction (5 cycles)
•N2 stripping
(by LAK N2 222Rn: 8 mBq/m3, Ar:
0.01 ppm, Kr: 0.03 ppt)
Internal view of CTF
[Borexino coll. Astrop. Phys. 8 1998]
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Baikal Summer School 20-27 July 2008
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Primary sources of radioimpurities
source
Typical
Concentrations
Borexino level
Removal
strategy
14C
Cosmic ray
activation of 14N
14C/ 12C~10-12
14C/ 12C<10-17
Old carbon (solvent
from oil)
7Be
Cosmic ray
Activation of
12C
~3 cpd/ton
< 0.01 cpd/ton
Distillation,
underground storage
238U, 232Th
Suspended dust,
organometallics
~ 1ppm in dust
~ 1ppb stainless steel
~ 1ppt IV nylon
~10-16g/g(PC)
Distillation, filtration
Knat
Suspended dust,
Contaminant found
in fluor
~ 1ppm in dust
<10-13g/g(PC)
Distillation, water
extraction , filtration
222Rn
Air and emanation
from materials
~ 10Bq / m3 in air
~ 70 mBq / m3 in PC
(0.3ev/day/100tons)
Nitrogen stripping
210Bi,210Po
210Pb
2 x 104 cpd/ton from
exposing a surface to
10Bq/m3 of 222Rn
<0.01 cpd/ton
Surface cleaning
85Kr, (39Ar)
air
1.1Bq/m3
(13mBq/m3 ) in air
0.16mBq/m3 (0.5 m Bq/m3 ) in N2
0.01 events/day/ton
Nitrogen stripping
Lino Miramonti
decay
Baikal Summer School 20-27 July 2008
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18 m
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Baikal Summer School 20-27 July 2008
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2002-2004
The project is stopped for local problems
2005
Re-commissioning of all the set ups
2006
Restart of all operations - detector filled with purified water
2007
Detector filled with purified scintillator (PC+1.5 g/l PPO), PC plus
quencher (5.0 g/l),purified water
May 15th 2007 Borexino starts the data taking with the detector completely filled.
water filling
May 15th, 2007
Scintillator filling
Liquid scintillator
Low Ar and Kr N2
Hight purity water
From Aug 2006
Lino Miramonti
From Jan 2007
Baikal Summer School 20-27 July 2008
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Specs: 232Th: 10-16 g/g
Background: 232Th content
Assuming secular equilibrium, 232Th is
measured with the delayed coincidence:
212Bi

 = 432.8 ns
212Po
2.25 MeV
a
212Pb
α=6.04 MeV
208Pb
212Bi
212Po
α=8.79 MeV
 = 432.8 ns
~800 keV eq.
208Tl
208Pb
z (m)
Events are mainly in the south vessel surface (probably particulate)
Only few
bulk candidates
R  x2  y2  z 2
(m)
Rc 
x2  y2
(m)
From 212Bi-212Po correlated events in the scintillator:
232Th: = 6.8 ± 1.5 ×10-18 g(Th)/g  0.25 cpd/100tons
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Baikal Summer School 20-27 July 2008
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Specs: 238U: 10-16 g/g
Background: 238U content
Assuming secular equilibrium, 238U is
measured with the delayed coincidence:
214Pb
214Bi
214Po
α=7.69 MeV
 = 236 ms
a 210Pb
214Bi 
214Po
~700 keV eq.
3.2 MeV
 = 236 ms
210Pb
210Bi
210Po
214Bi-214Po
z (m)
210Pb
214Bi-214Po
 = 240±8ms
Time ms
Rc 
x2  y2
(m)
From 214Bi-214Po correlated events in the scintillator:
238U: = 1.6 ± 0.1 ×10-17 g(U)/g  1.9 cpd/100tons
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Baikal Summer School 20-27 July 2008
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Background:
210Po
NOTES
•
The bulk 238U and 232Th contamination is
negligible
•
The 210Po background is NOT related neither to
238U contamination NOR to 210Pb contamination
214Pb
214Bi
214Po
α=7.7 MeV
210Po
decay time:
204.6 days
210Pb
210Bi
210Po
α=5.4 MeV
decays α: Q=5.4 MeV
light yield quenched by  13
210Po
206Pb
•
•
210Pb
Not in equilibrium with
210Po decays as expected
Lino Miramonti
!
210Bi
no direct evidence  free parameter in the total fit
(cannot be disentangled, in the 7Be energy range,
from the CNO)
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Background: 85Kr
85Kr
has an energy
spectrum similar to
the 7Be recoil electron
85Kr

85Rb
End point
687 keV
 = 10.76 y - BR: 99.56%
The 85Kr content in the scintillator was probed through the rare decay
sequence:
85
Kr 85mRb  e  e
85 m
Rb85Rb  
  1.5ms, BR  0.43%
that offers a delayed coincidence tag.
Our best estimate for the activity of 85Kr is 29±14 cpd/100 tons
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Baikal Summer School 20-27 July 2008
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Cosmic m rejection
SSS
m flux: 1.21±0.05 m-2 h-1
Inner Detector
m are detected in Outer Detector and Inner Detector;
Outer Detector
Outer Detector efficiency > 99%
Muon angular
distributions
Inner Detector m analysis is based on time pulse
shape variables
Estimated overall rejection factor: > 104
After cuts, m residual background: < 1 cpd/100 ton
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Position reconstruction
&
α/β discrimination
For each event the time and the
total charge are measured.
Absolute time is also provided (GPS)
The position of each event is reconstructed with an
algorithms based on time of flight fit to hit time
distribution of detected photoelectrons
(developed with MC, tested and validated in CTF cross checked and tuned in Borexino on selected
events 14C, 214Bi-214Po, 11C)
14C
Spatial resolution of
reconstructed events:
16 cm at 500 keV
(scaling as
α particles
β particles
Good separation at high energy
1/ 2
)
N pe
Radius (m)
The fit is compatible with the expected
r2-like shape with R=4.25m.
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Baikal Summer School 20-27 July 2008
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Fiducial volume
The nominal Inner Vessel radius is 4.25m (278 tons of scintillator = 315 m3)
The effective Inner Vessel radius has been reconstructed using:
•14C events,
•Thoron (=80s) on the IV surface (emitted by the nylon)
•External background gamma
•Teflon diffusers on the IV surface
maximum uncertainty : ~ ± 6%
z vs Rc scatter plot
Radial distribution
z < 1.8 m, was done to remove
gammas from IV endcaps
R2
gauss
FV
 from PMTs that penetrate the buffer
R  x2  y2  z 2
Rc  x 2  y 2
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Baikal Summer School 20-27 July 2008
51
Light Yield
&
Energy resolution
The Light Yield has been evaluated
fitting the 14C spectrum, and the
11C spectrum
11C
The light yield has been evaluated also by
taking it as free parameter in a global fit on
the total spectrum
14C,
14C
210Po-
210Po ,
7Be
Compton edge
spectrum (β- decay - 156 keV)
spectrum (+ decay - 960 keV)
Light Yield = 500 ±12 p.e./MeV
The 11C sample is selected through the triple
coincidence with muon and neutron. We limited the
sample to the first 30 min of 11C time profile, which
reduces the random coincidence to a factor 1/14.
Lino Miramonti
Energy resolution is approximately
5%
scaling as
E MeV 
Baikal Summer School 20-27 July 2008
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Expected Spectrum
Lino Miramonti
Baikal Summer School 20-27 July 2008
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Data: Raw Spectrum (No Cuts)
Lino Miramonti
Baikal Summer School 20-27 July 2008
192 days
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Data: Fiducial Cut (100 tons)
Lino Miramonti
Baikal Summer School 20-27 July 2008
192 days
55
Data: α/β Stat. Subtraction
Lino Miramonti
Baikal Summer School 20-27 July 2008
192 days
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Data: Final Comparison
Lino Miramonti
Baikal Summer School 20-27 July 2008
192 days
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New Results:192 Days
Lino Miramonti
Baikal Summer School 20-27 July 2008
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Systematic & Measurement
Expected 7Be interaction rate
for MSW-LMA oscillations:
Estimated 1σ Systematic Uncertainties* [%]
48 4 cpd / 100tons
High Z
44 4 cpd / 100tons
Low Z
Without including oscillations:
75 4 cpd / 100tons
Measured 7Be rate:
Lino Miramonti
*Prior to Calibration
49  3stat  4syst
cpd / 100tons
Baikal Summer School 20-27 July 2008
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Before BorexinoBaikal Summer School 20-27 July 2008
Lino Miramonti
60
νe Survival Probability
Global Analysis
•
We determine the survival probability for 7Be electron neutrinos
νe under the assumption of the high-Z SSM (Bahcall-Pena GaraySerenelli, BPS07)
Pee (7Be)  0.56  0.10 (1 ) at 0.862 MeV
•
Consistent with expectation from MSW-LMA
(S. Abe et al.,
arXiv:0801.4589v2)
Pee (7Be)  0.541 0.017
As determined from the
global fit to all solar
(except Borexino) and
reactor data
No oscillations hypothesis (Pee=1) excluded at 4σ C.L.
Lino Miramonti
Baikal Summer School 20-27 July 2008
61
νe Survival Probability
Global Analysis
•
We determine the survival probability for 7Be and pp electron
neutrinos νe under the assumption of the high-Z BPS07 SSM
and using input from all solar experiments (cfr. Barger et al., PRL 88,
011302 (2002))
Pee (7Be)  0.56  0.08
Pee ( pp)  0.57  0.09
Lino Miramonti
Baikal Summer School 20-27 July 2008
As determined from the
global fit to all solar
experiments
62
Pee (7Be)  0.56  0.08
Pee ( pp)  0.57  0.09
After Borexino
Lino Miramonti
Baikal Summer School 20-27 July 2008
63
7Be
Neutrinos Flux 
fi 
i
m easuredvalue

 iSSM predicted value
Best estimate ratio prior to Borexino, as determined with global fit to all solar
(except Borexino) and reactor data, with the assumption of the constraint on
solar luminosity: (M.C. Gonzalez-Garcia and Maltoni, Phys. Rep 460, 1 (2008)
24
f Be  1.0310..03
Ratio measured by Borexino assuming the high-Z BPS07 SSM and the
constraint on solar luminosity:
f Be  1.02  0.10
that corresponds to a
7Be neutrinos flux of:
Lino Miramonti
Baikal Summer School 20-27 July 2008
64
Constraints on pp and CNO fluxes
It is possible to combine the results obtained by Borexino on 7Be flux with those
obtained by other experiments to constraint the fluxes of pp and CNO ν;
The expected rate in Clorine and Gallium
experiments can be written as:
Rl SNU    Rl ,i f i P
source
l  Ga, Cl
experiment i  pp, pep, CNO,7Be,8B
l ,i
ee
i
Expected rate from
a source “i” in
experiment “l”
Ratio between
measured and
predicted flux


Survival probability averaged over
threshold for a source “i” in
experiment “l”
Rl,i and Pl,i are calculated in the hypothesis of high-Z SSM and MSW LMA
Lino Miramonti
Baikal Summer School 20-27 July 2008
65
Rk are the rates actually measured by Clorine and Gallium experiments:
f8B is measured by SNO and SuperKamiokande:
f7Be =1.02 ±0.10 is given by Borexino results;
Performing a 2 based analysis with the additional luminosity
constraint;
f pp  1.00400..008
020
(1 )
Which is the best determination of pp flux
fCNO  3.90 (90% C.L.)
Lino Miramonti
This result translates into a CNO contribution to
the solar neutrino luminosity < 3.4% (90% C.L)
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66
Borexino Perspectives (solar neutrinos)
CNO and pep  fluxes
Software algorithm based on 3-fold coincides analysis to subtract
cosmogenic 11C background
Muon track reconstruction
High precision measurements
Systematic reduction
Calibrations
8B at low energy
pp
CNO, pep
8B
pp seasonal variation
Lino Miramonti
Baikal Summer School 20-27 July 2008
67
Borexino Perspectives (beside solar neutrinos)
 Borexino will run comprehensive
program for study of antineutrinos (from
Earth, Sun, and Reactors)
 Borexino is a powerful observatory
for
neutrinos
from
Supernovae
explosions within few tens of kpc
 Best limit on neutrino magnetic
moment (5.4·10-11 mB 90%CL). Improve
by dedicated measurement with 51Cr
neutrino source
Events in 300 tons
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Conclusions
 The Borexino project seems to be a great success
 Due to the very high radiopurity Borexino can measure all the solar
neutrinos flux, included 7Be, pep,CNO and perhaps pp
 It is possible to probe the  oscillation model in the vacuum regime
and in the transition region, and to check possible
discrepancies
 These measurements provide new insights in the Solar model and
could fix some open problem (as the metallicity puzzle)
 The LNGS site is ideal to measure the geoneutrinos flux
 These measurements need a lot of care: we estimate other two
years, at least, to reach the results
Lino Miramonti
Baikal Summer School 20-27 July 2008
69
Borexino Collaboration
Genova
Milano
Princeton University
APC Paris
Perugia
Dubna JINR
(Russia)
Lino Miramonti
Kurchatov
Institute
(Russia)
Virginia Tech. University
Munich
(Germany)
Jagiellonian U.
Cracow
(Poland)
Heidelberg
(Germany)
Baikal Summer School 20-27 July 2008
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