1. Sudbury Neutrino Observatory
Results from the
Sudbury Neutrino Observatory
Dave Wark
Nikhef
January 11th, 2002

2. Fusion in the Sun pp 2H + e+ +e 2H + p 3He + 3He + 3He  4He + 2p
pep  2H + e
pp 2H + e+ +e
2H + p 3He +
3He + 3He  4He + 2p
3He + 4He 7Be +
e + 7Be  7Li +e
7Li + p  2 4He
p + 7Be  8B +
8B  8Be* + e+ +e
8Be* 2 4He
Dave Wark - Nikhef

3. Solar Neutrino Fluxes
Next three plots adapted from
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4. The Solar Neutrino Problem
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5. Helioseismology
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6. Helioseismology
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7. The Solar Neutrino Problem
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8. Neutrino Oscillations
Let us assume that neutrinos have (different) masses - Dm2
Let us assume that the mass eigenstates are not identical to the weak eigenstates
If we consider 2 flavours the mixing is characterized by a single angle q analogous to the Cabibbo angle in case of quarks
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9. Neutrino Oscillations
Or :
Recall that
Consider  = 45 nm ne nm
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10. Vacuum Oscillations
In general this leads to the disappearance of the original neutrino flavour
With the corresponding appearance of the “wrong” neutrino flavour
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11. The MSW effect
ne have an extra diagram for scattering from electrons (W as well as Z exchange)
gives ne an “effective mass” in matter proportional to the electron density Ne
can lead to an energy dependent resonant enhancement of oscillations for both large (LMA) and small (SMA) mixing angles ( m2/NeE )
The MSW effect
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12. Global fit, 8B Flux a free parameter
Includes:
Rates:
Homestake
SAGE
GALLEX/GNO
Super-K
Super-K spectra
day
night
From Bahcall, Krastev, and Smirnov; hep-ph/
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13. Sterile n solutions Includes: Rates: Homestake SAGE GALLEX/GNO Super-K
Super-K spectra
day
night
From Bahcall, Krastev, and Smirnov; hep-ph/
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14. SNO
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15. The SNO Detector Surface: 2 km Phototube Support 1000 tonnes D2O
Structure (PSUP)
1000 tonnes D2O
Acrylic Vessel
104 8” PMTs
6500 tonnes H2O
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16. n Reactions in SNO e p d + Þ n Þ ne only CC- e p d + Þ n
Good measurement of ne energy spectrum
Weak directional sensitivity  1-1/3cos(q)
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17. Čerenkov Light Production
Charged current interaction in D2O
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18. n Reactions in SNO e p d + Þ n Þ n + Þ p d Þ + Þ e ν Þ ne onlyCC - e p d + Þ n
Good measurement of ne energy spectrum
Weak directional sensitivity  1-1/3cos(q) NC x n + Þ p d Þ
Equal cross section
for all n types
Measure total 8B n flux from the sun. ES - + Þ e ν x Þ
All n types but
enhanced sensitivity
to ne
Low Statistics
Strong directional sensitivity
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19. The enemy….. bs and gs from decays in these chains interfere with our
signals at low energies
And worse, gs over 2.2 MeV
cause d + g  n + p
Design called for:
D2O < gm/gm U/Th
H2O < gm/gm U/Th
Acrylic < gm/gm U/Th
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20. Construction
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21. Water Systems
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22. SNO Water Assays Targets for D2O represent a 5%
background from d+g  n+p
Targets are set to reduce b-g
events reconstructing inside 6m
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23. Signals in SNO
NC Salt (BP98)
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24. Smoking Guns in SNO - 1 CC/ES Could also show significant effects!
Charged-Current to Neutral Current
ratio is a direct signature
for oscillations
CC/ES Could also show
significant effects!
0.15
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25. Charged-current spectrum is more sensitive to shape
Smoking Guns in SNO - 2 ES CC
Charged-current spectrum
is more sensitive to shape
distortions.
Day/Night
effects
possible
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26. A Neutrino Event
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27. Signals in SNO
NC Salt (BP98)
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28. Instrumental Backgrounds
Note Neck Tubes Fired
Electronic Pickup
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29. Instrumental Background Cuts
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30. How do we know this worked ?
We did it twice.
Two different semi-independent sets of cuts were developed.
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31. How do we know this worked?
Number of phototubes hit
Fraction of good events cut
Fraction of hits in a prompt time window
Mean angle between phototube hits
Contamination measured
with independent cuts
Signal loss measured with
calibration sources
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32. Solar Neutrino Spectrum
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33. Current SNO data set Data Period: 2/11/99  15/01/01
Livetime: Days
Data set 1: Analysis Data
used to develop the data analysis
~166 days livetime
Data set 2: Blind data
test for statistical bias
~75 days livetime
No statistically significant differences seen
results from full data set shown here
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34. SNO Livetime
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35. Manipulator
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36. SNO Energy Calibrations
252Cf neutrons
b’s from 8Li
g’s from 16N and t(p,g)4He
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37. Backgrounds from the Data
External g-ray background
bg background from the AV
bg background from the H2O
bg background from the PMTs
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38. Acrylic Vessel Assay (~1/10) the target level of 2 ppt U/Th
Every piece sampled and tested
Sample bonds tested
Direct Assay by Čerenkov light
AV well below
(~1/10)
the target level of
2 ppt U/Th
“Berkeley Blob”
9 +20  3 mg “Th” -5
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39. Signal Extraction Threshold set at Teff = 6.75 MeV
removes most of the neutrons
further reduces the background
Fit resulting events to Probability Density Functions (pdfs) in:
effective energy: Teff
volume weighted position: (R/RAV)3
angle from the Sun: cosq
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40. Signal Extraction
Teff
(R/RAV)3
cosq
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41. Signal Extraction Threshold set at Teff = 6.75 MeV
removes most of the neutrons
further reduces the background
Fit resulting events to Probability Density Functions (pdfs) in:
effective energy: Teff
volume weighted position: (R/RAV)3
angle from the Sun: cosq
Use maximum likelihood to extract components
CC = ± events
ES = ± events
neutrons = ± events
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42. SNO cosq distribution
Electron Angle with respect
to the direction from the Sun
ES: strongly peaked
CC: 1-1/3cosq
Neutrons: isotropic
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43. SNO energy spectrum from unconstrained fit
Data points derived
by fitting each energy
bin independently
Monte Carlo of
undistorted 8B
spectrum normalized
to the data
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44. SNO energy spectrum from an unconstrained fit
Ratio to BP2001:
0.347 ± 0.029
(Adding syst. bin by bin in quadrature give c2 of ~12 for 11 D.O.F.)
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45. SNO energy spectrum from an unconstrained fit
Ratio to BP2001:
0.347 ± 0.029
(Adding syst. bin by bin in quadrature give c2 of ~12 for 11 D.O.F.)
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46. SNO energy spectrum from an unconstrained fit
New Super K Flux
Ratio to BP2001:
0.347 ± 0.029
(Adding syst. bin by bin in quadrature give c2 of ~12 for 11 D.O.F.)
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47. Solar Neutrino Fluxes NB: All fluxes quoted are in units 106/cm2/sec
Absolute fluxes from constrained fit:
CC (8B) = 1.75 ± ± 0.05
(stat) (sys.) (theory)
ES (8B) = 2.39 ± 0.34
(stat) (sys.)
+0.16
- 0.14
SNO:
NB: All fluxes quoted are in
units 106/cm2/sec
Dave Wark - Nikhef

48. Systematic Flux Uncertainties
Error Source
Energy scale
Energy resolution
Non-linearity
Vertex shift
Vertex resolution
Angular resolution
High Energy ’s
Low energy background
Instrumental background
Trigger efficiency
Live time
Cut acceptance
Earth orbit eccentricity
17O, 18O
Experimental uncertainty
Cross-section
Solar Model
CC error (%)
-5.2, +6.1
±0.5
±3.1
±0.7
-0.8, +0.0
-0.2, +0.0
0.0
±0.1
-0.6, +0.7
±0.2
-6.2, +7.0
3.0
-16, +20
ES error (%)
-3.5, +5.4
±0.3
±0.4
±3.3
±2.2
-1.9, +0.0
-0.2, +0.0
-0.6, +0.0
0.0
±0.1
-0.6, +0.7
±0.2
-5.7, +6.8
0.5
-16, +20
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49. Solar Neutrino “Fluxes”
Absolute fluxes from constrained fit:
CC (8B) = 1.75 ± ± 0.05
(stat) (sys.) (theory)
ES (8B) = 2.39 ± 0.34
(stat) (sys.)
+0.16
- 0.14
SNO:
+0.08
- 0.07
ES (8B) = 2.32 ± 0.03
(stat) (sys.)
Super-K*
*S. Fukuda, et al., hep-ex/
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50. “Flux” Differences The hypothesis that this is a downward
CC at SNO vs ES at SNO
ES - CC = 0.64 ±  1.6 effect
SNO
CC at SNO vs ES at SK
ES - CC = 0.57 ±  3.35 effect SK
SNO
The hypothesis that this is a downward
statistical fluctuation is ruled out at 99.96%
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51. John Bahcall has been right all these years!
Ftotal vs. Fe
You can extract the total neutrino flux from
these results:
SNO (8B) = 5.44 ±0.99  106 cm-2s-1
-SK
This can be compared to the SSM prediction:
+1.01
- 0.81
SSM (8B) =  106 cm-2s-1
John Bahcall has been right all these years!
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52. Using the 8B flux to constrain G and WIMPS
See Lopes and Silk, astro-ph/
See Lopes and Silk, astro-ph/
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53. Allowed Solutions for Neutrino Oscillations
Flavour Oscillations
Sterile Oscillations
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54. Equalizing SNO/SK n response
CC and ES have different En response
However, choosing different thresholds can compensate
For the current analysis,
Tthresh = 6.75 MeV for SNO
and 8.6 MeV for Super-K
equalize response to few %
From G.L. Fogli et al., hep-ph/
For these thresholds the
“fluxes”still differ by
0.53 ± 0.17
Sterile oscillations ruled out
by this test at > 3s
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55. Allowed Solutions for Neutrino Oscillations
Flavour Oscillations
Sterile Oscillations
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56. Oscillation Analyses including SNO
Barger, Marfatia and Whisnant: hep-ph/
Oscillations to partially sterile neutrinos still allowed
Fogli et al.: hep-ph/
Purely sterile oscillations ruled out at >3s
SMA flavoured oscillations also ruled out
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57. Allowed regions from Fogli et al.
Before SNO
After SNO
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58. Oscillation Analyses including SNO
Barger, Marfatia and Whisnant: hep-ph/
Oscillations to partially sterile neutrinos still allowed
Fogli et al.: hep-ph/
Purely sterile oscillations ruled out at >3s
SMA flavoured oscillations also ruled out
Bahcall, Gonzalez-Garcia, Pena-Garay: hep-ph/
No, at 3s everything still allowed
Bandyopadhyay et al.: hep-ph/
Includes SNO energy spectrum
SMA ruled out
Berezinsky: hep-ph/
SNO was right about everything….
Krastev and Smirnov: hep-ph/
No they weren’t, but neither are the others…..
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59. What is going on? Why do these analyses differ? Which one is right?
Different handling of spectral oversampling
Slightly differences in the methods
Which one is right?
Beats me…..
As Rutherford said, if you need a statistical test, you did the wrong experiment.
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60. The Right Experiment SNO Neutral Current Measurement
Pure D2O - data in can, results soon
Salt data now being taken
Higher efficiency for neutron capture
Capture signal at higher E, clear of background
Independent test for NC/CC discrimination
Different systematics
Discrete NCDs to be deployed next
Stringent test for non-electron neutrino appearance
Dave Wark - Nikhef

61. Conclusions The SNO detector is working and taking beautiful data.
The CC rate measured in SNO is incompatible with the Super-K ES rate.
This is strong evidence (>99.8% c.l.) for the appearance of m or t neutrinos from the Sun.
Sterile and Just-So2 oscillations are excluded by these results at >99.8% c.l.
The 8B n flux from the Sun is now measured to be in agreement with the predictions of the Standard Solar Model.
+Super-K+T2 b decay  < Wn < 0.18
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62. Outlook NC measurements in pure D2O
These results are just the first of what SNO will produce.
The conclusions listed on the preceeding slide are systematics dominated. They will be severely tested by new measurements:
NC measurements in pure D2O
Day/night in pure D2O
The same measurements with NaCl added
The same measurements with the NCDs
Borexino and KamLAND will give additional information in the near future
The future - SIREN, LENS, etc.
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63. Outlook
Solar Neutrinos have demonstrated (confirmed?) that neutrinos have mass and undergo flavour oscillations
Now we must understand why…..
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