1. Results and Prospects for SNO
Low Energy Threshold Analysis (LETA)
Motivations
Analysis Details
Results
Status of `three-phase’ Analysis
Summary and Other Recent Results
Josh Klein, for the SNO Collaboration
University of Pennsylvania
15 June 2010

2. Sudbury Neutrino Observatory
neutrino reactions on deuterons
National
Geographic
Neutrino-Electron Scattering (ES)
Charged Current (CC)
Neutral Current (NC)
Signal rates determined by statistical fit

3. Three Phases of SNO Phase I: Just D2O
Simple detector configuration, clean measurement
Low neutron sensitivity
Poor discrimination between neutrons and electrons
Phase II: D2O + NaCl
Very good neutron sensitivity
Better neutron electron separation
Phase III: D2O + 3He Proportional Counters
Good neutron sensitivity
Great neutron/electron separation

4. Low Energy Threshold Analysis
Motivations: ne Statistics CC
En=6 MeV ES
En=6 MeV
Night
Day

5. Low Energy Threshold Analysis
Motivations: NC Precision
nx (NC) Statistics
Breaking NC/CC Covariance
Phase I (D2O) NC
+74%
+68%
Phase II
(D2O+NaCl) I
“Beam Off”
Low n capture eff. II
“Beam On”
High n capture eff.

6. Low Energy Threshold Analysis
Overview
Key components:
Joint-Phase (I+II) fit for all signals and remaining bkds
Reduction of Backgrounds
Reduction of Systematic Uncertainties
`Float’ Dominant Uncertainties in Fit
Needed to rework SNO’s entire analysis chain and simulation, from measurement of charge pedestals to final fit methods.
Results:
8B flux measured by NC rates
Bin-by-bin electron energy spectrum using CC & ES
Parameterized Psurv(En) (New)
Two-flavor and three-flavor extraction of mixing params.

7. Low Energy Threshold Analysis
Signal Extraction Fit (Signal PDFs)
Monte Carlo
Not used
(unconstrained in fit)
Teff (MeV)
cosqsun
(R/RAV)3
Isotropy =
1-D projections of 3-D and 4-D PDFS

8. Low Energy Threshold Analysis
Low Energy Backgrounds
Cosmic rays < 3/hour
Teff>3.5 MeV
All events
( but only ~5000 ns)
D2O
Acrylic Vessel
H2O
}×{ +
PMT 208Tl
Acrylic Vessel Surface Neutrons [(α,n) reactions]
214Bi (U, Rn)
208Tl (Th)
24Na (neutron activation of salt)
= 12 external bkds + 5 internal bkds
(most backgrounds constrained by ex-situ radioassays)
For each phase

9. Low Energy Threshold Analysis
Low Energy Backgrounds
Kinetic Energy Spectrum
New Threshold = 3.5 MeV MC
PMT b-gs
internal (D2O)
external (AV + H2O)
NC+CC+ES (Phase II)
Old threshold
3 neutrino signals
+ 17 backgrounds
ALL MC!!

10. Low Energy Threshold Analysis
Signal Extraction Fit (3 out of 17(x2) Background PDFs)
Monte Carlo
Teff (MeV)
cosqsun
(R/RAV)3
Isotropy =
1-D projections of 3-D and 4-D PDFS

11. Low Energy Threshold Analysis
Background Reduction: Energy Resolution
Time Residual (ns)
Prompt Timing Cut
Late Timing Cut
Rayleigh Scatter
(used in prior analyses)
Using all hits increased hit statistics by ~12%
->6% reduction in resolution
~60% reduction internal bkds
`Prompt’ (direct) light easy to model: we know the path traveled

12. Low Energy Threshold Analysis
Background Reduction: New Cuts
Only information is PMT charges, times, and hit patterns
4 KS tests of PMT pattern against single Cherenkov e-
1 KS test of PMT times against Cherenkov e-
3 cuts on various isotropy parameters
2 cuts on energy reconstruction uncertainty
In-time ratio vs. Nhit to remove misreconstructed events

13. Low Energy Threshold Analysis
Background Reduction: New Cuts
`Early’ Charge to cut PMT b-gs
Fiducial Volume β γ
High charge early in time
Note: This would have been impossible if we hadn’t fixed `little’ things like charge pedestals

14. Low Energy Threshold Analysis
Special Case: PMT b-g PDFs
Not enough CPUs to simulate sample of events Use data instead
PassFail
FailPass
FailFail
PassPass
Early charge probability
Early charge probability
In-time ratio
In-time ratio
`Bifurcated’ analysis
NPF = e1(1-e2)Nb
NFP = (1-e1) e2Nb
NFF = (1-e1)(1-e2)Nb
NPP = e1e2Nb + Ns
NPMT= NPP – Ns
= NFP * NPF / NFF

15. Low Energy Threshold Analysis
Systematic Uncertainties: Brief Summary 0% 1% 3% 4% 2%
n capture
Teff scale
Fiducial volume I II
LETA I
LETA II
N/A
I=D2O
II=D2O+Salt
b14
(isotropy)

16. Low Energy Threshold Analysis
Systematic Uncertainties
And shows clear ES peak, even at 3.5MeV threshold

17. Low Energy Threshold Analysis
Tests of PDF shapes
Comparison of 208Tl calibration source data to MC
Run near the AV
(to model AV 208Tl events)
And shows clear ES peak, even at 3.5MeV threshold

18. Low Energy Threshold Analysis
Tests of PDF shapes
Distributed Rn Spike
And shows clear ES peak, even at 3.5MeV threshold
Fit to spike energy spectrum allowing Teff scale to float: shift is 0±0.6%

19. Low Energy Threshold Analysis
Signal Extraction Fit
(3 signals+17 backgrounds)x2, and pdfs are multidimensional:
ES, CC
NC, backgrounds
Two distinct methods:
1. Maximum likelihood with binned pdfs:
 Manual scan of likelihood space
Data helps constrain systematics
`human intensive’
2. Kernel estimation---ML with unbinned pdfs:
Further improve syst meast by using data to constrain values of syst pars
Allows full `floating’ of systematics, incl. resolutions
CPU intensive---use graphics card!

20. Low Energy Threshold Analysis
Fit Results: Binned fit, 1D Projections
And shows clear ES peak, even at 3.5MeV threshold

21. Low Energy Threshold Analysis
8B Flux Results with `unconstrained’ CC spectrum
And shows clear ES peak, even at 3.5MeV threshold
LETA A
LETA B

22. Low Energy Threshold Analysis
`Unconstrained’ CC Electron Spectrum
And shows clear ES peak, even at 3.5MeV threshold

23. Low Energy Threshold Analysis
`Unconstrained’ CC Electron Spectrum
Flat:2 = 21.52/15 d.o.f.
And shows clear ES peak, even at 3.5MeV threshold

24. Low Energy Threshold Analysis
Direct fit to data for Psurv(En)
Parameterize distortion to ne spectrum with quadratic
Psurv is independent of any flux model:
CC and ES rates constrained to be less than NC
This helps separate signals and backgrounds: PDFs are now 4D
PeeDAY(E) = c0 + c1 (E - 10 MeV)
+ c2 (E - 10 MeV)2
PeeASYM(E) = a0 + a1 (E - 10 MeV)
PeeNIGHT(E) = PeeDAY(E) x [1 + (1/2)*PeeASYM(E)]
[1 – (1/2)*PeeASYM(E)]
And shows clear ES peak, even at 3.5MeV threshold
Note: Fit is now in En, not Teff

25. Direct Fit for Energy-Dependent Survival Probability
Previous global best-fit LMA point:
tan212 = 0.468, m2 = 7.59x10-5 eV2
8B = %
No distortion, no D/N:
2 = 1.94 / 4 d.o.f.
LMA-prediction:
2 = 3.90 / 4 d.o.f.
DAY
NIGHT
ASYM

26. Comparisons of 8B Spectra
J.L. Raaf, Boston University
SNO
Day
Night
Borexino
arXiv: v2

27. Oscillation Analyses: SNO Only
LETA paper 2009:
LETA joint-phase fit
+ Phase III (3He)
Best-fit point:
tan212=0.437±0.058
m2=1.15x eV2
(LOW)
SNO Collaboration, Phys. Rev C81, 55504

28. Solar + KamLAND 2-flavor Overlay
Brief History
KamLAND Collab, Phys.Rev.Lett.90:021802,2003.

29. Solar + KamLAND 2-flavor Overlay
Brief History
KamLAND collaboration

30. Solar + KamLAND 2-flavor Overlay
Brief History
S. Abe et al. (KamLAND Collaboration), PRL 100, (2008)

31. Solar + KamLAND 2-flavor Overlay
Brief History
LETA paper 2009:
LETA joint-phase fit
+ Phase III
+ all solar expts
+ KamLAND

32. Solar + KamLAND 2-flavor Overlay
LETA paper 2009:
LETA joint-phase fit
+ Phase III
+ all solar expts
+ KamLAND
2-flavor overlay
2 model

33. Oscillation Analyses: Solar + KamLAND
LETA paper 2009:
LETA joint-phase fit
+ Phase III
+ all solar expts
+ KamLAND
Best-fit LMA point:
tan212 =
(q12= deg)
sin2q12-1/3=
m2 = 7.59x10-5 eV2 ( )
2 model
8B uncert = %

34. Solar + KamLAND 3-flavor Overlay
LETA paper 2009:
LETA joint-phase fit
+ Phase III
+ all solar expts
+ KamLAND
3-flavor fit/overlay
->Pointed out by many authors
Best-fit:
sin213= x10-2
sin213 < (95% C.L.)
3 model

35. ``Three-Phase’’ Analysis
Combine LETA+Phase III (3He) in single fit
Pulse Shape Analysis to separate 3He signal from background
Constrain 3-phase fit using 3He neutron count
Output is 8B flux using NC + Psurv(En) +

36. ``Three-Phase’’ Analysis
Pulse Shape Analysis
Two 2-D Cuts:
Hypothesis Test 1
Hypothesis Test 2
Fit to counter pulse energy spectrum used to constrain number of neutrons in full fit
See poster by R. Martin, N. Oblath, N. Tolich

37. ``Three-Phase’’ Analysis
Pulse Shape Analysis
All phases combined with Psurv(En) fit
Expected Dm2 improvement
Also: expect to bring limits on hep down by x2
See poster by P-L. Drouin, C. Howard, N. Barros

38. Other SNO Results Low-multiplicity burst search
High frequency periodicity search
Expected Sensitivity
Neutrons and spallation products
See poster by A. Anthony,
ApJ. 710:
See poster by J. Loach

39. Summary
LETA analysis improved precision on NC by more than factor of 2.
Lowest analysis threshold yet achieved by water Cherenkov technique
Low E spectrum (still) consistent with no distortion
First model-independent fit for solar ne survival probability
3-flavor analysis shows non-zero q13 but consistent with q13=0:
Expect further improvement with 3-phase analysis
Just a few other things left to do…
sin213= x10-2
sin213 < (95% C.L.)

41. Systematic Uncertainties
Position
Old
New
Central runs remove source positioning offsets,
MC upgrades reduce shifts
Fiducial volume uncertainties (> factor of 3 improvement:
Old: Phase I ~ ±3% Phase II ~ ±3%
New: Phase I ~ ±1% Phase II ~ ±0.6%
Tested with: neutron captures, 8Li, outside-signal-box ns

42. Systematic Uncertainties
Isotropy (b14)
MC simulation upgrades provide biggest source of improvement
Tests with muon `followers’, Am-Be source, Rn spike
b14 Scale uncertainties (factor of 2 improvement):
Old: Phase I --- , Phase II = ±0.85% electrons, ±0.48% neutrons
New: Phase I ±0.42%, Phase II =±0.24% electrons,+0.38%-0.22% neutrons

43. 8B Flux Result
NC = %
And shows clear ES peak, even at 3.5MeV threshold
J. N. Bahcall, A. M. Serenelli, and S. Basu, AstroPhys. J. 621, L85 (2005)

44. Monte Carlo Upgrades Calibrations
Parameters for simulation measured and tested with sources
Laser source (optics/timing)
16N  6.13 MeV ’s
Radon `spikes’
Neutrons 6.25 MeV ’s
pT  19.8 MeV ’s
8Li  ’s, E<14 MeV
Encapsulated U and Th sources

45. Systematic Uncertainties
Energy Scale
No correction
With correction
16N calibration source
6.13 MeV gs
Volume-weighted uncertainties:
Old: Phase I = ±1.2% Phase II = ±1.1%
New: Phase I = ±0.6% Phase II = ±0.5% (about half Phase-correlated)
Tested with: Independent 16N data, n capture events, Rn `spike’ events…

46. New Cuts
Summary
~80% reduction in external bkds

47. Direct Fit for Energy-Dependent Survival Probability
Previous global best-fit LMA point:
tan212 = 0.468, m2 = 7.59x10-5 eV2
NIGHT
DAY
And shows clear ES peak, even at 3.5MeV threshold

48. Survival Probability DAY NIGHT
And shows clear ES peak, even at 3.5MeV threshold
NIGHT

49. Survival Probability DAY NIGHT
And shows clear ES peak, even at 3.5MeV threshold
NIGHT

50. Survival Probability DAY NIGHT
And shows clear ES peak, even at 3.5MeV threshold
NIGHT

51. Survival Probability DAY NIGHT
And shows clear ES peak, even at 3.5MeV threshold
NIGHT

52. Oscillation Analyses: Global Solar
LETA paper 2009:
LETA joint-phase fit
+ Phase III
+ all solar expts
Best-fit LMA point:
tan212 = ( )
m2 = 5.89x10-5 eV2 ( )
And shows clear ES peak, even at 3.5MeV threshold