1. Results and Future Challenges of the Sudbury Neutrino Observatory Neil McCauley University of Pennsylvania WIN 2005 : Delphi, Greece. 7 th June 2005

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

3. The SNO Collaboration 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 Y.D. Chan, X. Chen, C. Currat, K.M. Heeger, K.T. Lesko, A.D. Marino, E.B. Norman, C.E. Okada, A.W.P. Poon, S.S.E. Rosendahl, R.G. Stokstad Lawrence Berkeley National Laboratory M.G. Boulay, S.R. Elliott, J. Heise, A. Hime, R.G. Van de Water, J.M. Wouters Los Alamos National Laboratory T. Kutter Louisiana State University 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 Queen’s 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

4. The Sudbury Neutrino Observatory 2039m to surface 1000 tonnes of D 2 O 7000 tonnes of H 2 O Norite rock 6800 ft level INCO’s Creighton Mine Sudbury, Ontario 12m diameter acrylic vessel 17m diameter PMT support structure with ~9500 PMTs Urylon liner and radon seal

5. Sensitivity to Neutrino Flavour: Signals in SNO Charged Current D+ e  p+p+e - Electron energy closely corresponds to neutrino energy.  CC = e Neutral Current D+ x  p+n+ x Equally sensitive to all active neutrino flavors. Threshold 2.2MeV.  NC = e +   Elastic Scattering e - + x  e - + x Good directional sensitivity. Enhanced e sensitivity.  ES = e + 0.154 

6. Neutron Detection: The 3 Phases of SNO. Phase 1: Pure D 2 O. Nov 1999 – May 2001 : 306 days. Neutrons Capture on D Detect 6.25MeV  -ray. Phase 2: D 2 O+NaCl Jul 2001-Sep 2003 : 391 days. Neutrons Capture on 35 Cl Detect multiple  -rays.  E=8.6MeV Phase 3: 3 He Proportional Counters (NCD) Nov 2004-Dec 2006 Neutrons capture on 3 He Captures are detected in the counters.

7. Why add salt? 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. E/MeV Events/Day Detection Eff /% r/cm

8. Measuring Isotropy Use the angle between PMT hits from the fit event vertex. Decompose distribution in spherical harmonics. Use  14 =  1 + 4  4 Note that  14 depends on energy. Contribution of  14 uncertainty is relatively large. 4% of CC,NC flux.

9. Radioactive Backgrounds Three low energy decay of concern. 208 Tl (Th chain) 214 Bi (U chain / Rn) 24 Na (Na activation) Two sources of background. Neutrons (E  >2.2MeV) Cherenkov Tail. T eff >5.5MeV New Calibration using Rn spikes. Two monitoring techniques Ex-situ: Radio Assays. In-situ: Cherenkov light. Fit to isotropy distribution at low energy. Low energy isotropy fit.  14 T eff /MeV Rn spike. Data:MC comparison

10. Extraction of Neutrino Signals. ESNCCC E/MeV (r/600cm) 3 cos(   ) Isotropy 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.

11. Fit Results Full Salt Data Set: 391 Days. Fit for CC,NC,ES and External Neutrons. nucl-ex/0502021 Isotropy RadiusDirection

12. Neutrino Fluxes Fit Using: T eff >5.5MeV r fit <550cm Dominant systematics  14 Mean Value Energy Scale Radial Bias Neutron Capture (NC) Angular Resolution (ES) Flavour content of solar flux.

13. ES events Electron Energy Spectra Fit to data was done without CC/ES energy constraints. Spectra Extracted from Fit. Beware Correlations. Systematic CC i  CC j Statistical CC i  NC  CC j CC events CC Spectrum and LMA

14. Day-Night Asymmetry A NC floating A NC  0 T eff /MeV A CC Can carry out many analyses. A NC floating A NC  0 Include/Remove CC,ES spectral constraints. Statistics Dominated Results. A CC = -0.037±0.071 A NC  0 CC,ES Spectrum Unconstrained Extract asymmetry spectrum. Best fit LMA shown. Combine with D 2 O result. A e,combined = 0.037±0.040 A NC  0 CC/ES Spectrum Constrained

15. 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. All Solar Data Solar + KamLAND

16. Phase 3 : 3 He 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.

17. 3 He Counters. n+ 3 He  p+T Measure Current vs Time in the proportional counters. Expect capture efficiency: ~25% on 3 He ~20% on D Unique identification of neutrons. Substantially reduce CC  NC correlation. Reduce uncertainty in CC/NC Reduce uncertainty in  12 Baseline Analysis: Background Free Region. E/KeV Pulse Width /  s

18. Instrumental Backgrounds. A fork cut To carry out neutron analysis, we need to remove instrumental backgrounds. We are developing a suite of cuts. Time/ns A fork event Time/ns Current /Arb Units A neutron Current /Arb Units Time/ns

19. 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.

20. Enhanced Spectral Analysis The current LMA paradigm suggests that the e survival probability increases sharply between 1-5MeV Our current threshold is T e >5.5MeV 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 E /MeV SNO CC Effective Threshold.

21. Enhanced Spectral Analysis To lower the threshold and improve spectral determination we must fight backgrounds. Cherenkov Tail Events 208 Tl, 214 Bi, 24 Na D 2 O and H 2 O tails. Neutrons Background Neutrons NC events. 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. Reduce covariance between neutrons and electrons. Isotropy. 3 He Counters. Multi-Phase fits. Fit the background and signal simultaneously.

22. Improved Energy Estimation Use “Late” Light. Increase Hit Statistics Reduce Energy Resolution. Model Local Variations. Reduce Energy Uncertainties. (R/R AV ) 3 16 N

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.