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Borexino and Solar neutrinos
Igor MachulinRRC “Kurchatov Institute”
On behalf of the Borexino CollaborationQuarks2008/May/
Quarks2008/May/
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
St.-Petersburg INF (Russia)
99,77%p + p d+ e+ +
e
0,23%p + e - + p d +
e
3He+3He+2p
3He+p+e+
+e
~210-5 %84,7%
13,8%
0,02%13,78%3He + 4He 7Be +
7Be + e- 7Li + e7Be + p 8B
+
d + p 3He +
7Li + p ->+
8B 8Be*+ e+ +e
2
Solar neutrinos from nuclear reactions in the Sun core , dominant pp cycle.
Quarks2008/May/ Igor Machulin , RRC “Kurchatov Institute “
Solar neutrinos from nuclear reactions in the Sun core, sub-dominant CNO cycle
LCNO / Lsun < 5-6%
(GALLEX/GNO+SAGE)
from CNO cycle had not yet been observed
Quarks2008/May/ Igor Machulin , RRC “Kurchatov Institute “
…dominates in stars with more mass
than our sun…
=>Large astrophysical relevance
Solar neutrino spectrum according to the SSM (Bahcall-Serenelli 2005)
Borexino energy range for Solar neutrino measurements in Real-time
Quakrs2008/May/ Igor Machulin , RRC “Kurchatov Institute “
Oscillations and matter effects
Oscillation length ~ 102 km
=> oscillation smeared out
and non-coherent
Effective e mass (due to forward scattering on electrons) is enhanced by a potential A
A ~ GFNeE2
=> for E > 1 MeV
matter effect dominates
and leads to an enhanced e suppression for those energies…
MSW Effect in Sun
Missing info herebefore BOREXINO
Now additionalImprovement on
uncertaintyon pp-e flux
Vaccum regime Matter regime
1 10 MeV
Experimental site for Borexino - Gran Sasso Laboratory
Laboratori Nazionali del Gran Sasso near L’Aquila, INFN.
Underground Lab provides shielding from cosmic background of 3500 m water equivalent
Quarks2008/May/ Igor Machulin , RRC “Kurchatov Institute “
Water Tank: and n shield water Čherenkov detector208 PMTs in water2100 m3
20 legs
Scintillator:278 t PC+PPO (1,5 g/l) in150 m thick nylon vessel
Stainless Steel Sphere:2212 photomultipliers 1350 m3
2 Nylon vessels:Inner: 4.25 mOuter: 5.50 m
Borexino Detector Design
BOREXINO Design is based on the principles of graded shielding
Buffer :890 t PC+DMP(5
g/l)
Quarks2008/May/ Igor Machulin , RRC “Kurchatov Institute “
PhotoMultiplierTube -PMT
Installation of PMTs on the sphere
Nylon vessel installation
Quarks2008/May/ Igor Machulin , RRC “Kurchatov Institute “
Detector filling completed and data taking started- May 15th, 2007
Quarks2008/May/ Igor Machulin , RRC “Kurchatov Institute “
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* 10-11B level
• Geo and reactor antineutrinos
• Supernova detection
• Rare processes studies (electron decay, neutrino decay etc.)
e Lie Be 77
Monochromatic E=862 KeV
SSM=4.8x109 / (s*cm2)
Quarks2008/May/ Igor Machulin , RRC “Kurchatov Institute “
Detection principles x + e- -> x + e-~10-44 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 eventsThe key requirement for measurements is the
extremely low radioactive contamination !To be less than Solar neutrino rate ~50 counts/(day*100 tons)
Simulated electron spectrum in Borexino
from Solar (SSM+LMA) and backgrounds
pp7Be
CNO, pep
8B
Electron recoil spectrum due to solar neutrino scattering
Quarks2008/May/ Igor Machulin , RRC “Kurchatov Institute “
Light Yield and Energy Resolution
14C spectrum in Borexino detector(end point of decay-156 keV)
The Light Yield is calculated by global fit on the experimental Borexino spectrum:
14C – 156 keV end-point,
11C – + decay, Q=1.98 MeV
7Be Compton edge - 665 keV
210Po alpha peak resolution - 210Po
Light yield = 500 pe/MeV Energy resolution is obtained from
210Po alpha-decays peak ( Q=5.41 MeV, quenched by a factor ~13)
/E = 5% at 1 MeV
14C content in Borexino scintillator- 2.7 * 10-18 14C/12C
Quarks2008/May/ Igor Machulin , RRC “Kurchatov Institute “
Cosmic muon rejection in Borexino
after μ cut
• Cosmic μ flux - 1.21±0.05 h-1m-2
• μ detected in Outer and Inner Detector • Outer Detector efficiency > 99%• Inner Detector μ analysis is based
on time pulse shape variables
• Estimated overall rejection factor: > 104
After cuts, background:
< 1 c/d/100 ton Measured μ angular distributions
Quarks2008/May/ Igor Machulin , RRC “Kurchatov Institute “
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.
Spatial resolution of reconstructed events: 16 cm at 500 keV scaling as (Npe)-1/2
Quarks2008/May/
external eventson the surface
R=4.25m.
Radius (m)
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 |z|<1.7m
Total effective fiducial volume after the position cut - 78.5 tons
Igor Machulin , RRC “Kurchatov Institute “
Radius cut
Internal events R<4.25m.
/ discrimination of events
particles
Small deformation due to averageSSS light reflectivity
particles
near the 210Po peak low energy side of the 210Po peak
2 gaussians fit 2 gaussians fit
Full separation at high energy
ns
Gatti parameter Gatti parameter Quarks2008/May/
GATTI Parameter is applied to the statistical subtraction of
Igor Machulin , RRC “Kurchatov Institute “
Background - 232Th content in scintillator
212Bi 212Po 208Pb
= 432.8 ns
2.25 MeV ~800 KeV eq.
=423±42 ns
232Th: (6.8+-1.5)×10-18 g/g – 0.25 cpd/100 tons
z (m
)
2 2cR x y (m)Time
(ns)
Quarks2008/May/ Igor Machulin , RRC “Kurchatov Institute “
212Bi-212Po correlated events in the scintillator
Background - 238U content in scintillator
214Bi 214Po 210Pb
= 236 s
3.2 MeV ~700 KeV eq.
=240±8 s
Time (s)
2 2cR x y (m)
z (m
)
238U: (1.9+-0.3)×10-17 g/g - 2 cpd/100 tons
Quarks2008/May/ Igor Machulin , RRC “Kurchatov Institute “
214Bi-214Po correlated events in the scintillator:
Background- other contaminants in scintillator
(~ 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 200 days-removed from the spectrum via discrimination technique
85Kr - -decayQ=687 keV
210Po - -decayQ=5.41 MeV , LY quenched by a factor~13
studied by delayed coincidence: 85Rb85Kr 85mRb
= 1.46 s - BR: 0.43%
514 keV
173 keV
the 85Kr contamination (29+-14) counts/day/100 ton
Quarks2008/May/ Igor Machulin , RRC “Kurchatov Institute “
New experimental results for 192 days of live time (16 May 2007 – 12 April)
Cou
nts
/(5
ph
otoe
lect
ron
s *
day
* 1
00 t
ons)
– to be published these days at arXiv:08xxxxxv1
Quarks2008/May/ Igor Machulin , RRC “Kurchatov Institute “
Photoelectron raw charge spectrum in Borexino
Spectral fit of the energy spectrum with statistical subtraction (192 days)
Quarks2008/May/ Igor Machulin , RRC “Kurchatov Institute “
• Oscillation predictions for Mikheev-Smirnov Large Mixing Angle Solution:In Solar model BPS07(GS98) HighZ 48 ± 4 c/100t/dIn Solar model BPS07(AGS05) LowZ 44 ± 4 c/100t/d• No oscillation hypothesis
75 ± 4 c/100t/d
Survival probability for 7Be νe - Pee=0.56 ± 0.10
The no oscillation hypothesis Pee=1 is rejected at 4 level
BOREXINO new result192 days of live time
49 ± 3stat ± 4syst 7Be ν counts / (day · 100 ton)
Quarks2008/May/ Igor Machulin , RRC “Kurchatov Institute “
Prospects of Borexino- pep and CNO Solar fluxes - Main problem: 11C production by cosmic
11C 11B +e+ +e (Q = 1.98 MeV, T1/2=20.4min), tagging in 3-fold delayed coincidence , n (~ms) ,
track reconstruction + position of n-capture veto region around this
position for ~ 1 hour. Required rejection factor ~ 10
- neutrino magnetic moment search :
CNO
- 8B Solar flux measurements
pep11C
Sensitivity on at few * 10-11B level (like in best reactor experiments);
with Solar and dedicated measurement with artificial 51Cr source
Quarks2008/May/2008 Igor Machulin , RRC “Kurchatov Institute “
- Geo & reactor antineutrinos
Prospects of Borexino
- Supernova neutrinos detection
Detection channel Any hierarchy
Inverse-Beta Decay(E > 1.8 MeV)
79
-p ES(E > 0.25 MeV)
55
12C()12C* (E = 15.1 MeV)
17
Standard SN at 10kpc
Quarks2008/May/ Igor Machulin , RRC “Kurchatov Institute “
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 e and anti-e at the level of 10-2. The beam to Gran Sasso will restart in summer 2008.
Direction of detected passing muons, generated by CERN beam in Borexino detector (Sept.-Oct. 2007)
Quarks2008/May/ Igor Machulin , RRC “Kurchatov Institute “
Total Scintillator Mass 0.2
Fiducial Mass Ratio 6.0
Live Time 0.1
Detector Resp. Function
6.0
Cuts Efficiency 0.3
Total 8.5
Systematic (1σ) Error [%]
More Info
Spectral fit of the energy spectrum (192 days) before statistical subtraction
Quarks2008/May/ Igor Machulin , RRC “Kurchatov Institute “
Neutrino Oscillations
(1,2,3)
( , , )
i i
i
U
neutrino mass eigenstates
neutrino flavor eigenstates e
cos , sinij ij ij ijc s
U:
Pontecorvo-Maki-Nakagawa-Sakata matrix (the analog of the CKM matrix in the hadronic sector of the Standard Model).
i : 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.
The two neutrino case
cos sin
sin cosU
The probability that a neutrino originally of flavor will later be observed as having another flavor is given by:
222 2
2( ) sin 2 sin 1.267
m L GeVP t
eV km E
Oscillation parameters: Solarolar
Atmospheric
2m0.6 5 20.48.0 10 eV
0.6 3 20.52.4 10 eV
0 2.4
2.233.9
045 7
Solar neutrino oscillations and atmospheric oscillations are decoupled:
Chooz reeactor result - Theta(1,3) < 13O