1. Evidence of Neutrino Oscillation from SNO Chun Shing Jason Pun Department of Physics The University of Hong Kong Presented at the HKU Neutrino Workshop 28 November, 2003

2. Outline 1.The Solar Neutrino Problem 2.(Brief) Descriptions of SNO 3.Results from SNO 4.Future (and present) plans for SNO * Acknowledgement: This presentation borrows heavily from SNO member, Dr Alan W.P. Poon (LBL).

3. 1. The Solar Neutrino Problem Solar neutrinos provide a unique opportunity to study physics beyond the standard model. Huge flux: Long baseline: 1 AU = 1.5x10 8 km Relatively low neutrino energy (~ MeV)

4. 7 Be+p  8 B+  8 B  8 Be * +e + + e 8 Be *  4 He+ 4 He 1. pp chain and Standard Solar Model p+p  2 H+e + + e p+e+p  2 H+ e p+ 2 H  3 He+  3 He+ 4 He  7 Be+  7 Be+ e -  7 Li+ e 7 Li+p  4 He+ 4 He 3 He+p  4 He+ e + + e 85%15% 0.02% [pp  ] [pep  ] [hep  ] [ 7 Be  ] [ 8 B  ] Overall: 4p + 2e  4 He + 2 e + 26.7MeV

5. Combining with detailed model of solar evolution, we get the Standard Solar Model (SSM) (cm -2 s -1 ) (CC) SNO(NC)

6. 1.Solar Neutrino Problem Increasing detection energy threshold The discrepancy suggests either (a)Solar models are incomplete and/or incorrect (b)Neutrinos undergo flavor-changing transformation along the way from the Sun to Earth

7. 1. Astrophysical Solution to the Problem Reduce the solar core temperature T c to lower the predicted flux, e.g. F n ( 8 B)  T 25 BUT: Poor agreement with other parameters SSM accurately describes many observations Speed of sound in solar interior

8. 1.Neutrino Oscillation

9. Combination of baseline/neutrino-energy (L/E) probes different regions in the (  m 2,tan 2  ) parameter space. Mikheyev-Smirnov- Wolfenstein (MSW) effect: resonance enhancement of the oscillation amplitude in dense matter (e.g. solar interior) (Murayama 2003)

10. 2. The Sudbury Neutrino Observatory (SNO) 1000 tons D 2 O 2km underground in Sudbury, Canada 9456 20-cm PMTs in a 12m diameter vessel (56% coverage)

12. 2. Neutrino reactions at SNO CC - epd  e p NC xx    npd ES --    e e x x e-e- d p p e Charged Current: Measurement of e spectrum Weak directionality: 1-0.340cos  Neutral Current: Measure total solar 8 B flux flux  e      Elastic Scattering: Low statistics, strong directionality flux  e  ≈    ≈    d p n x x x x e-e- e-e-

13. 2. Neutrino Oscillation at SNO If no oscillation, solar neutrinos would be pure e. Measure the ratio, If e transform into other flavors, then Alternatively, can also measure the ratio and detect transformation if

14. 3. Results from SNO Electron neutrino event recovered from the Cherenkov radiation of the e -. e- 42 o cone angle

15. 3. NC measurement at SNO Measurement of the NC is the most important for SNO Key: Detect high energy neutrons Three phases of measurements with different techniques and systematics Phase I: Pure D 2 O (Nov 99 – May 01) Phase II: Pure D 2 O + NaCl (Jul 01 – Sep 03) Phase III: D 2 O + 3 He Proportional Counters (Nov 03 – ?)

16. 3. Phase I (Pure D 2 O) CC, ES, some NCs n + 2 H → 3 H +  (6.25 MeV),  = 0.5 mb Low neutron capture and detection efficiencies (  n ~ 14% above threshold)

17. 3. Phase I, PRL 87 (2001) 071301 Measured  CC ( e ) and compare with accurate ES results from Super-K [PRL 86 (2001) 5651] 3.3  1.6  SK ES (1  ) Excludes pure e  sterile at 3.1 

18. 3. Phase I, PRL 89 (2002) 011301, 02 All pure D 2 O data used Direct measurement of total 8 B flux  NC ( X ) 1.6 

19. 3. Main Results (Phase I) A.Exclude   = 0 at 5.3s B.SSM prediction verified (flux in units of 10 -6 cm -2 s -1 ): Bahcall, Pinsonneault & Basu (2001 ） ApJ, 555, 990

20. 3. Phase II (Pure D 2 O + NaCl) 2 tonnes of NaCl added CC, ES, enhanced NCs n + 35 Cl → 36 Cl* +  ’s (8.6 MeV),  = 44 b High neutron capture efficiency with higher energy release (  n ~ 40% above threshold)

22. 3. Phase II, nucl-ex/0309004 Spectral distributions of the ES and CC events are not constrained to the standard 8 B spectral shape. Measured total 8 B flux (in units of 10 -6 cm -2 s -1 ): Recall

23. SNO Only All Solar experiments + KamLAND 3. Constraints on  m 2 and tan 2  Best fit:  m 2 = 4.7x10 -5, tan 2  = 0.43 Best fit:  m 2 = 6.5x10 -5, tan 2  = 0.40

24. 4. Phase III (Pure D 2 O + 3 He) Arrays of 3 He proportional counters (Neutral Current Detectors, NCD) inserted n + 3 He → p + 3 H + 760 keV (  n ~ 37%) Motives: –CC, NC measured in separate data streams –Different systematic uncertainties –Search for direct evidence of MSW effect, from CC spectral shape distortion.

25. 4. Phase III (Pure D 2 O + 3 He) Nov 2003 – ? 40 strings on 1-m grid 440m total active length. Installed by a small remote control submarine

26. The SNO Collaboration T. Kutter, C.W. Nally, S.M. Oser, C.E. Waltham 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, R.J. Hemingway, I. Levine, C. Mifflin, E. Rollin, O. Simard, D. Sinclair, N. Starinsky, G. Tesic, D. Waller Carleton University P. Jagam, H. Labranche, J. Law, I.T. Lawson, B.G. Nickel, R.W. Ollerhead, J.J. Simpson University of Guelph J. Farine, F. Fleurot, E.D. Hallman, S. Luoma, M.H. Schwendener, R. Tafirout, C.J. Virtue Laurentian University Y.D. Chan, X. Chen, 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, T.J. Bowles, S.J. Brice, M.R. Dragowsky, S.R. Elliott, M.M. Fowler, A.S. Hamer, J. Heise, A. Hime, G.G. Miller, R.G. Van de Water, J.B. Wilhelmy, J.M. Wouters Los Alamos National Laboratory S.D. Biller, M.G. Bowler, B.T. Cleveland, G. Doucas, J.A. Dunmore, H. Fergani, K. Frame, N.A. Jelley, 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, M. Dunford, W.J. Heintzelman, C.C.M. Kyba, N. McCauley, V.L. Rusu, R. Van Berg University of Pennsylvania S.N. Ahmed, M. Chen, F.A. Duncan, E.D. Earle, B.G. Fulsom, H.C. Evans, G.T. Ewan, K. Graham, A.L. Hallin, W.B. Handler, P.J. Harvey, M.S. Kos, A.V. Krumins, J.R. Leslie, R. MacLellan, H.B. Mak, J. Maneira, A.B. McDonald, B.A. Moffat, A.J. Noble, C.V. Ouellet, B.C. Robertson, P. Skensved, M. Thomas, Y.Takeuchi Queen’s University D.L. Wark Rutherford Laboratory and University of Sussex R.L. Helmer TRIUMF A.E. Anthony, J.C. Hall, J.R. Klein 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, R.G.H. Robertson, M.W.E. Smith, L.C. Stonehill, B.L. Wall, J.F. Wilkerson University of Washington