Borexino and Solar neutrinos

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Borexino and Solar neutrinos

• Igor Machulin
• RRC Kurchatov Institute
• On behalf of the Borexino Collaboration

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Borexino collaboration
Genova
Princeton University
APC Paris
Virginia Tech. University
Munich (Germany)
Dubna JINR (Russia)
Kurchatov Institute (Russia)
Jagiellonian U. Cracow (Poland)
Heidelberg (Germany)
St.-Petersburg INF (Russia)
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Solar neutrinos from nuclear reactions in the
Sun core , dominant pp cycle.
99,77 p p ? d e ?e
0,23 p e - p ? d ?e
2?10-5
84,7
d p ? 3He ?
13,8
3He 4He ?7Be ?
0,02
13,78
7Be e- ? 7Li ?e
7Be p ? 8B ?
3He3He??2p
3Hep??e?e
7Li p -gt??
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Solar neutrinos from nuclear reactions in the
Sun core, sub-dominant CNO cycle
n from CNO cycle had not yet been observed
LCNO
/ Lsun
lt 5-6
(GALLEX/GNOSAGE)
dominates in stars with more mass than our
sun gtLarge astrophysical relevance
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Solar neutrino spectrum according to the SSM
(Bahcall-Serenelli 2005)
Borexino energy range for Solar neutrino
measurements in Real-time
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Oscillations and matter effects
Oscillation length 102 km gt oscillation
smeared out and non-coherent Effective ne
mass (due to forward scattering on electrons) is
enhanced by a potential A A GFNeE2 gt for E gt 1
MeV matter effect dominates and leads to an
enhanced ne suppression for those energies MSW
Effect in Sun
Missing info here before BOREXINO Now
additional Improvement on uncertainty on pp-ne
flux
1
10 MeV
Vaccum regime Matter regime
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Experimental site for Borexino - Gran Sasso
Laboratory
Laboratori Nazionali del Gran Sasso near
LAquila, INFN. Underground Lab provides
shielding from cosmic background of 3500 m water
equivalent
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Borexino Detector Design
Stainless Steel Sphere 2212 photomultipliers
1350 m3
Scintillator 278 t PCPPO (1,5 g/l) in 150 mm
thick nylon vessel
Buffer 890 t PCDMP(5 g/l)
2 Nylon vessels Inner 4.25 m Outer 5.50 m

• Water Tank
• g and n shield
• water Cherenkov
• detector
• 208 PMTs in water
• 2100 m3

20 legs
BOREXINO Design is based on the principles of
graded shielding
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PhotoMultiplierTube -PMT
Nylon vessel installation
Installation of PMTs on the sphere
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Detector filling completed and data taking
started- May 15th, 2007
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Borexino Physics

• Be-7 neutrino detection in real time mode
• pep, CNO and pp neutrino detection
• B-8 neutrino detection
• Measurement of neutrino magnetic moment
• with the sensitivity of few 10-11mB level
• Geo and reactor antineutrinos
• Supernova detection
• Rare processes studies (electron decay,
  neutrino decay etc.)

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Detection principles

• nx e- -gt nx e- s10-44 cm2
• Liquid scintillator (photon yield 10000
  photons/MeV)
• High Light Yield 500 photoelectrons/MeV
• Good energy resolution 5 for 1 MeV
• Very low energy threshold 60 keV
• Good position reconstruction of events
• The key requirement for measurements is the
• extremely low radioactive contamination
  !
• To be less than Solar neutrino rate 50
  counts/(day100 tons)

Electron recoil spectrum due to solar neutrino
scattering
Simulated electron spectrum in Borexino from
Solar ? (SSMLMA) and backgrounds
pp
7Be
CNO, pep
8B
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Light Yield and Energy Resolution
14C spectrum in Borexino detector (end point of
b? decay-156 keV)
The Light Yield is calculated by global fit on
the experimental Borexino spectrum 14C 156
keV end-point, 11C ? decay, Q1.98 MeV 7Be n
Compton edge - 665 keV 210Po alpha peak
resolution - s 210Po Light yield 500 pe/MeV
Energy resolution is obtained from 210Po
alpha-decays peak ( Q5.41 MeV, quenched by a
factor 13) s/E 5 at 1 MeV
14C content in Borexino scintillator- 2.7
10-18 14C/12C
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Cosmic muon rejection in Borexino
after µ cut

• Cosmic µ flux - 1.210.05 h-1m-2
• µ detected in Outer and Inner Detector
• Outer Detector efficiency gt 99
• Inner Detector µ analysis is based
• on time pulse shape variables
• Estimated overall rejection factor gt 104
• After cuts, m background
• lt 1 c/d/100 ton

Measured µ angular distributions
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Position reconstruction of events

• Based on time of flight fit to the time
  distribution of detected photoelectrons
• cross checked on selected events 14C,
  214Bi-214Po, 11C, external gammas, teflon laser
  light diffusers on the Inner Vessel detector
  surface.

external events on the surface R4.25m.
Radius cut
Internal events Rlt4.25m.
Radius (m)
Spatial resolution of reconstructed events 16
cm at 500 keV scaling as (Npe)-1/2
1,25 m of scintillator in all directions assures
a shielding for the background from the PMTs and
the nylon of the vessel. Additional cut
zlt1.7m
Total effective fiducial volume after the
position cut - 78.5 tons
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a/b discrimination of events
Full separation at high energy
Small deformation due to average SSS light
reflectivity
a particles
b particles
ns
GATTI Parameter is applied to the statistical
subtraction of a
near the 210Po peak
low energy side of the 210Po peak
2 gaussians fit
2 gaussians fit
a/b Gatti parameter
a/b Gatti parameter
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Background - 232Th content in scintillator
212Bi-212Po correlated events in the scintillator
z (m)
?42342 ns
Time (ns)
(m)
232Th (6.8-1.5)10-18 g/g 0.25 cpd/100 tons
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Background - 238U content in scintillator
214Bi-214Po correlated events in the scintillator
z (m)
?2408 ? s
Time (?s)
(m)
238U (1.9-0.3)10-17 g/g - 2 cpd/100 tons
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Background- other contaminants in scintillator
210Po - a-decay, Q5.41 MeV , LY quenched by a
factor13

• ( 60 cpd/ton was inserted during
• the scintillation filling)
• 210Po background is related neither to 238U
  contamination nor to 210Pb contamination
• it is decaying with a t?200 days
• -removed from the spectrum via a/b
• discrimination technique

85Kr - b -decay, Q687 keV
studied by delayed coincidence
the 85Kr contamination (29-14) counts/day/100
ton
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New experimental results for 192 days of live
time (16 May 2007 12 April)
Photoelectron raw charge spectrum in Borexino
to be published these days at arXiv08xxxxxv1
Counts/(5 photoelectrons day 100 tons)
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Spectral fit of the energy spectrum with a/b
statistical subtraction (192 days)
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BOREXINO new result 192 days of live time
49 3stat 4syst 7Be ? counts / (day 100 ton)

• Oscillation predictions
• for Mikheev-Smirnov Large Mixing Angle Solution
• In Solar model BPS07(GS98) HighZ 48 4
  c/100t/d
• In Solar model BPS07(AGS05) LowZ 44 4
  c/100t/d
• No oscillation hypothesis
• 75 4 c/100t/d
• Survival probability for 7Be ?e -
  Pee0.56 0.10
• The no oscillation hypothesis Pee1 is rejected
  at 4s level

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BOREXINO
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Prospects of Borexino

• pep and CNO Solar n fluxes
• Main problem 11C production by cosmic m

• 11C -gt 11B e ne (Q 1.98 MeV, T1/220.4min),
  tagging in 3-fold delayed coincidence m, n (ms)
  ,
• m track reconstruction
• position of n-capture veto region around this
  position for 1 hour.
• Required rejection factor 10

CNO
11C
pep

• 8B n Solar flux measurements

• neutrino magnetic moment search

Sensitivity on mn at few 10-11mB level (like
in best reactor experiments) with Solar n and
dedicated measurement with artificial 51Cr n
source
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Prospects of Borexino

• - Geo reactor antineutrinos

- Supernova neutrinos detection
Standard SN at 10kpc
Detection channel Any hierarchy
Inverse-Beta Decay (En gt 1.8 MeV) 79
n-p ES (En gt 0.25 MeV) 55
12C(n,n)12C (Eg 15.1 MeV) 17
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Monitoring of CERN neutrino beam

• The SPS CERN primary proton beam at 400 GeV is
  focused onto a graphite target, producing
  secondary mesons. Neutrinos are produced in a 900
  m length vacuum tunnel by the decay in flight of
  high momentum p and K selected and focused
  towards the Gran Sasso Laboratory - 730 km .
• The neutrino beam contains predominantly muon
  neutrinos with an average energy of 17 GeV, and a
  contamination of anti -nm, ne and anti-ne at
  the level of 10-2. The beam to Gran Sasso will
  restart in summer 2008.

Direction of detected passing muons, generated by
CERN n beam in Borexino detector (Sept.-Oct.
2007)
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More Info
Systematic (1s) Error
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Spectral fit of the energy spectrum (192 days)
before a/b statistical subtraction
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Neutrino Oscillations
U Pontecorvo-Maki-Nakagawa-Sakata matrix (the
analog of the CKM matrix in the hadronic sector
of the Standard Model).
Non-zero only of neutrinos are Majorana
particles and do not enter the oscillation
phenomena regardless. If neutrinoless double beta
decays occurs, these factors influence its
rate. The phase factor is non-zero only if
neutrino oscillation violates CP symmetry.
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The two neutrino case
The probability that a neutrino originally of
flavor will later be observed as having
another flavor is given by

Solarolar
Atmospheric
Oscillation parameters
Solar neutrino oscillations and atmospheric
oscillations are decoupled Chooz reeactor
result - Theta(1,3) lt 13O