Results and Future Challenges of the Sudbury Neutrino Observatory

1
Results and Future Challenges of the Sudbury
Neutrino Observatory

• Neil McCauley
• University of Pennsylvania
• WIN 2005 Delphi, Greece.
• 7th June 2005

2
Overview

• The Sudbury Neutrino Observatory.
• Results from the Salt Phase.
• Future Challenges
• Phase 3 3He Counters.
• Reducing the energy threshold in SNO.
• Conclusions.

3
The SNO Collaboration
S.D. Biller, M.G. Bowler, B.T. Cleveland, G.
Doucas, J.A. Dunmore, H. Fergani, K. Frame, N.A.
Jelley, J.C. Loach, S. Majerus, G. McGregor,
S.J.M. Peeters, C.J. Sims, M. Thorman, H. Wan
Chan Tseung, N. West, J.R. Wilson, K.
Zuber Oxford University E.W. Beier, H. Deng, M.
Dunford, W. Frati, W.J. Heintzelman, C.C.M. Kyba,
N. McCauley, M.S Neubauer, V.L. Rusu, R. Van
Berg, P. Wittich University of Pennsylvania S.N.
Ahmed, M. Chen, F.A. Duncan, E.D. Earle, H.C.
Evans, G.T. Ewan, B. G Fulsom, K. Graham, A.L.
Hallin, W.B. Handler, P.J. Harvey, C. Howard,
L.L Kormos, M.S. Kos, C. Kraus, C.B. Krauss,
A.V. Krumins, J.R. Leslie, R. MacLellan, H.B.
Mak, J. Maneira, A.B. McDonald, B.A. Moffat,
A.J. Noble, C. Ouellet, B.C. Robertson, P.
Skensved, M. Thomson, Y. Takeuchi, A.
Wright Queens University D.L. Wark Rutherford
Appleton Laboratory R.L. Helmer TRIUMF A.E.
Anthony, J.C. Hall, M. Huang, J.R. Klein, S.
Seibert University of Texas at Austin T.V.
Bullard, G.A. Cox, P.J. Doe, C.A. Duba, J.A.
Formaggio, N. Gagnon, R. Hazama, M.A. Howe, S.
McGee, K.K.S. Miknaitis, N.S. Oblath, J.L.
Orrell, K. Rielage, R.G.H. Robertson, M.W.E.
Smith, L.C. Stonehill, B.L. Wall, J.F.
Wilkerson University of Washington

• C.W. Nally, S.M. Oser, T. Tsui, C.E. Waltham,
  J.Wendland
• University of British Columbia
• J. Boger, R.L. Hahn, R. Lange, M. Yeh
• Brookhaven National Laboratory
• A.Bellerive, X. Dai, F. Dalnoki-Veress, R.S.
  Dosanjh,
• D.R. Grant, C.K. Hargrove, L. Heelan, R.J.
  Hemingway,
• I. Levine, C. Mifflin, E. Rollin, O. Simard, D.
  Sinclair,
• N. Starinsky, G. Tesic, D. Waller
• Carleton University
• M. Bergevin,P. Jagam, H. Labranche, J. Law, I.T.
  Lawson,
• B.G. Nickel, R.W. Ollerhead, J.J. Simpson
• University of Guelph
• B. Aharmim J. Farine, F. Fleurot, E.D. Hallman,
  A. Krüger,
• S. Luoma, M.H. Schwendener, R. Tafirout, C.J.
  Virtue
• Laurentian University

4
The Sudbury Neutrino Observatory
2039m to surface
6800 ft level INCOs Creighton Mine Sudbury,
Ontario
5
Sensitivity to Neutrino FlavourSignals in SNO
6
Neutron Detection The 3 Phases of SNO.

• Phase 1 Pure D2O.
• Nov 1999 May 2001 306 days.
• Neutrons Capture on D
• Detect 6.25MeV g-ray.
• Phase 2 D2ONaCl
• Jul 2001-Sep 2003 391 days.
• Neutrons Capture on 35Cl
• Detect multiple g-rays. SE8.6MeV
• Phase 3 3He Proportional Counters (NCD)
• Nov 2004-Dec 2006
• Neutrons capture on 3He
• Captures are detected in the counters.

7
Why add salt?
Detection Eff /

• Increase in Capture Cross Section.
• 0.5mb?44b
• Increase in visible Cerenkov energy.
• More neutrons above threshold.
• Detection efficiency 14.4 ? 40.7
• Multiple g-rays in the final state.
• Events are more isotropic.
• Can statistically separate neutrons from
  electrons.

r/cm
8
Measuring Isotropy

• Use the angle between PMT hits from the fit event
  vertex.
• Decompose distribution in spherical harmonics.
• Use b14 b1 4b4
• Note that b14 depends on energy.
• Contribution of b14 uncertainty is relatively
  large.
• 4 of CC,NC flux.

9
Radioactive Backgrounds

• Three low energy decay of concern.
• 208Tl (Th chain)
• 214Bi (U chain / Rn)
• 24Na (Na activation)
• Two sources of background.
• Neutrons (Eggt2.2MeV)
• Cherenkov Tail. Teffgt5.5MeV
• New Calibration using Rn spikes.
• Two monitoring techniques
• Ex-situ Radio Assays.
• In-situ Cherenkov light.
• Fit to isotropy distribution at low energy.

10
Extraction of Neutrino Signals.
ES
NC
CC

• Carry out a maximum Likelihood fit of the data to
  signal PDFs.
• 4 Dimensional fit.
• Energy.
• Radius.
• Direction.
• Isotropy (salt only).
• In salt isotropy allows us to drop CC and ES
  energy PDFs.
• Model Independent Flux Extraction.
• Extract the Spectrum.

E/MeV
(r/600cm)3
cos(q?)
Isotropy
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Fit Results
Isotropy

• Full Salt Data Set 391 Days.
• Fit for CC,NC,ES and External Neutrons.
• nucl-ex/0502021

Radius
Direction
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Neutrino Fluxes

• Fit Using
• Teffgt5.5MeV
• rfitlt550cm
• Dominant systematics
• b14 Mean Value
• Energy Scale
• Radial Bias
• Neutron Capture (NC)
• Angular Resolution (ES)

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Electron Energy Spectra

• Fit to data was done without CC/ES energy
  constraints.
• Spectra Extracted from Fit.
• Beware Correlations.
• Systematic CCi?CCj
• Statistical CCi?NC?CCj

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Day-Night Asymmetry

• Can carry out many analyses.
• ANC floating
• ANC ? 0
• Include/Remove CC,ES spectral constraints.
• Statistics Dominated Results.
• ACC -0.0370.071
• ANC ? 0
• CC,ES Spectrum Unconstrained
• Extract asymmetry spectrum.
• Best fit LMA shown.
• Combine with D2O result.
• Ae,combined 0.0370.040
• ANC ? 0
• CC/ES Spectrum Constrained

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Interpretation of Results.

• With SNO results
• Large mixing angle regions are selected.
• Maximal mixing is rejected.
• Add other solar data.
• LMA region is selected.
• Add KamLAND data.

16
Phase 3 3He Counters.

• Timeline to phase 3
• Salt Removal.
• Sept 2003.
• PMT Electronics Upgrade.
• Oct/Nov 2003.
• Counter Deployment.
• Nov2003-May2004.
• Commissioning.
• May Nov 2004.
• Phase 3 Production Data. Taking Commences.
• Nov 2004.

40 Strings on 1 m grid. Total Active length 398m.
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3He Counters.
Baseline Analysis Background Free Region.

• n3He ?pT
• Measure Current vs Time in the proportional
  counters.
• Expect capture efficiency
• 25 on 3He
• 20 on D
• Unique identification of neutrons.
• Substantially reduce CC?NC correlation.
• Reduce uncertainty in CC/NC
• Reduce uncertainty in q12

Pulse Width / ms
E/KeV
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Instrumental Backgrounds.

• To carry out neutron analysis, we need to remove
  instrumental backgrounds.
• We are developing a suite of cuts.

Time/ns
A fork cut
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PMT Data in Phase 3.

• Presence of proportional counters blocks lights.
• Adds effective attenuation.
• Fewer hits per MeV
• Breaks Spherical Symmetry
• New Background Sources.
• U/Th on the counters.

Compensate by Lower Trigger Threshold. Lower
Channel Thresholds. Increased PMT High Voltage.
More Complex Signal Extraction.
More Complicated insitu Background Analysis New
variables Distance to Nearest Counter.
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Enhanced Spectral Analysis
SNO CC Effective Threshold.

• The current LMA paradigm suggests that the ne
  survival probability increases sharply between
  1-5MeV
• Our current threshold is Tegt5.5MeV
• Q value for CC reaction is 1.4MeV
• Lower our threshold to look for the turn up.
• Positively identify LMA.
• Look for new physics.
• Non standard interactions.

Miranda, Tortola, Valle hep-ph/0406280
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Enhanced Spectral Analysis

• Reduce Cherenkov tail
• Reduce total background.
• Select data with lower background levels.
• Lower background levels in the water.
• Reduce background in the signal box
• Reduce energy resolution.
• Reduce energy systematics.
• Improve reconstruction.

• To lower the threshold and improve spectral
  determination we must fight backgrounds.
• Cherenkov Tail Events
• 208Tl,214Bi,24Na
• D2O and H2O tails.
• Neutrons
• Background Neutrons
• NC events.

• Reduce covariance between neutrons and electrons.
• Isotropy.
• 3He Counters.
• Multi-Phase fits.
• Fit the background and signal simultaneously.

22
Improved Energy Estimation
Model Local Variations. Reduce Energy
Uncertainties.
16N
Use Late Light. Increase Hit Statistics Reduce
Energy Resolution.
(R/RAV)3
23
Other Physics Topics

• Solar Neutrino Topics
• hep Neutrinos.
• Periodicity
• Muons
• Atmospheric Neutrino Oscillations via
  Through-Going Muons.
• Measure flux normalzation above the Horizion.
• Muon Spallation.
• Exotic Physics
• Proton Decay
• Neutron AntiNeutron Oscillations.
• Supernovae

24
Conclusions

• SNO results show that neutrinos change flavour.
• Along with other data the LMA neutrino
  oscillation solution is selected.
• Phase 3 is underway.
• Further reductions in the size of the LMA region
  are expected.
• SNO plans an enhanced spectral analysis to look
  for positive signatures of LMA.