The Sudbury Neutrino Observatory

Transcription

1 The Sudbury Neutrino Observatory First Results GordonMcGregor (University of Oxford) for the SNO Collaboration XXXVIIth Rencontres de Moriond March 12 th 2002

2 Nuclear Fusion pp 2 H + e + +ν e 2 H + p 3 He +γ 3 He + 3 He 4 He + 2p pep 2 H + ν e 3 He + 4 He 7 Be +γ e + 7 Be 7 Li +ν e 7 Li + p 2 4 He p + 7 Be 8 B +γ 8 B 8 Be * + e + +ν e 8 Be * 2 4 He 2

3 Solar Neutrino Problem 1968 Homestake 600 tonnes C 2 Cl 4 ν e + 37 Cl 37 Ar+ e 1989 Kamiokande 2000 tonnes H 2 O ν e + e ν e + e 1990 Sage 1992 Gallex 90 tonnes Ga ν e + 71 Ga 71 Ge+ e 1998 Super-K tonnes H 2 O ν e + e ν e + e Solar Model, Experiments Or Neutrino Physics Wrong ν e ν µ or ν τ? 3

4 J. Boger, R. L Hahn, J.K. Rowley, M. Yeh Brookhaven National Laboratory I. Blevis, F. Dalnoki-Veress, W. Davidson, J. Farine, D.R. Grant, C. K. Hargrove, I. Levine, K. McFarlane, C. Mifflin, T. Noble, V.M. Novikov, M. O'Neill, M. Shatkay, D. Sinclair, N. Starinsky Carleton University J. Bigu, J.H.M. Cowan, E. D. Hallman, R.U. Haq, J. Hewett, J.G. Hykawy, G. Jonkmans, A. Roberge, E. Saettler, M.H. Schwendener, H. Seifert, R. Tafirout, C. J. Virtue. Laurentian University Y. D. Chan, X. Chen, M. C. P. Isaac, K. T. Lesko, A. D. Marino, E. B. Norman, C. E. Okada, A. W. P. Poon, A. R. Smith, A. Schülke, R. G. Stokstad. Lawrence Berkeley National Laboratory T. J. Bowles, S. J. Brice, M. Dragowsky, M.M. Fowler, A. Goldschmidt, A. Hamer, A. Hime, K. Kirch, G.G. Miller, J.B. Wilhelmy, J.M. Wouters. Los Alamos National Laboratory E. Bonvin, M.G. Boulay, M. Chen, F.A. Duncan, E.D. Earle, H.C. Evans, G.T. Ewan, R.J. Ford, A.L. Hallin, P.J. Harvey, J.D. Hepburn, C. Jillings, H.W. Lee, J.R. Leslie, H.B. Mak, A.B. McDonald, W. McLatchie, B. Moffat, B.C. Robertson, P. Skensved, B. Sur. Queen's University S. Gil, J. Heise, R. Helmer, R.J. Komar, T. Kutter, C.W. Nally, H.S. Ng,Y. Tserkovnyak, C.E. Waltham. University of British Columbia T.C. Andersen, M.C. Chon, P. Jagam, J. Law, I.T. Lawson, R. W. Ollerhead, J. J. Simpson, N. Tagg, J.X. Wang University of Guelph J.C. Barton, S.Biller, R. Black, R. Boardman, M. Bowler, J. Cameron, B. Cleveland, X. Dai, G. Doucas, J. Dunmore, H. Fergani, A.P. Ferraris, K.Frame, H. Heron, C. Howard, N.A. Jelley, A.B. Knox, M. Lay, W. Locke, J. Lyon, S. Majerus, N. McCaulay, G. McGregor, M. Moorhead, M. Omori, N.W. Tanner, R. Taplin, M. Thorman, P. Thornewell. P.T. Trent, D.L.Wark, N. West, J. Wilson University of Oxford E. W. Beier, D. F. Cowen, E. D. Frank, W. Frati, W.J. Heintzelman, P.T. Keener, J. R. Klein, C.C.M. Kyba, D. S. McDonald, M.S.Neubauer, F.M. Newcomer, S. Oser, V. Rusu, R. Van Berg, R.G. Van de Water, P. Wittich. University of Pennsylvania Q.R. Ahmad, M.C. Browne, T.V. Bullard, P.J. Doe, C.A. Duba, S.R. Elliott, R. Fardon, J.V. Germani, A.A. Hamian, R. Hazama, K.M. Heeger, M. Howe, R. Meijer Drees, J.L. Orrell, R.G.H. Robertson, K. Schaffer, M.W.E. Smith, T.D. Steiger, J.F. Wilkerson. University of Washington R.G. Allen, G. Buhler, H.H. Chen* University of California, Irvine * Deceased 4

5 The SNO Detector 1000 tonnes D 2 O 12 m Diameter Acrylic Vessel 1700 tonnes Inner Shielding H 2 O Support Structure for 9500 PMTs, 60% coverage 5300 tonnes Outer Shield H 2 O Urylon Liner and Radon Seal 5

6 Construction 6

7 n Reactions in SNO CC ν e + d p + p + - e -Good measurement of ν e energy spectrum -Weak directional sensitivity 1-1/3cos(θ) - ν e only. NC ν + d p + n + x ν x -Measure total 8 B ν flux from the sun. -Equal cross section for all ν types ES ? x e? x e -Low Statistics -All n types but enhanced sensitivity to ν e -Strong directional sensitivity 7

8 Signals in SNO NC Salt (BP98) 8

9 A Neutrino Event 9

10 Solar Neutrino Fluxes Absolute fluxes from constrained fit: SNO: F CC ( 8 B) = 1.75 ± ± (stat) (sys.) (theory) SNO: F ES ( 8 B) = 2.39 ± (stat) (sys.) Super-K * F ES ( 8 B) = 2.32 ± (stat) (sys.) *S. Fukuda, et al., hep-ex/

11 SNO CC spectrum normalised to undistorted 8 B spectrum No evidence for shape distortion Super-K Ratio to BP2001: ±

12 Systematic Uncertainties Energy (MeV) Source CC (%) ES (%) Energy scale +6.1, , -3.5 Energy resolution ±0.5 ±0.3 Energy scale non-linearity ±0.5 ±0.4 Vertex accuracy ±3.1 ±3.3 Vertex resolution ±0.7 ±0.4 Angular resolution ±0.5 ±2.2 High energy g +0, , -1.9 Low energy background Instrumental background +0.0, , -0.5 Trigger effi ciency Live Time ±0.1 ±0.1 Cut acceptance +0.7, , -0.6 Earth orbit eccentricity ±0.2 ± O, 18 O Experimental uncertainty +7.0, , -5.7 Cross section Solar model +20, , -16 N(HE γ events): <10 events (68% CL) 12

13 Flux Differences CC at SNO vs ES at SNO Φ ES - Φ CC = 0.64 ± σ effect SNO SNO CC at SNO vs ES at SK ΦSK ES - Φ CC SNO= 0.57 ± σ effect The hypothesis that this is a downward statistical fluctuation is ruled out at 99.96% 13

14 F mt vs. Fe Φ SNO ( 8 B) = 5.44 ± cm -2 s -1 +SK Φ SSM ( 8 B) = cm -2 s -1 The Standard Solar Models are correct 14

15 Post-SNO 2n Active Oscillation Analysis Oscillations to purely sterile neutrinos are ruled out. Fogli et al. 21 June

16 SNO s Current Analyses NC from lower analysis threshold Shape analysis from pure D 2 O data Day/night analysis hep-neutrino analysis Muons Seasonal and other Exotica Salt! 16

17 The enemy.. βs and γs from decays in these chains interfere with our signals at low energies And worse, γs over 2.2 MeV cause d + γ n + p Design called for: D 2 O < gm/gm U/Th H 2 O < gm/gm U/Th Acrylic < gm/gm U/Th 17

18 Sources of Activity in SNO 18

19 Water Purification and Assay MnOx 224 Ra, 226 Ra extraction Purification decay products counted Assay of in electrostatic counters 224 Ra, 226 Ra HTiO Th, Ra, & Pb extraction Purification chemically stripped and Assay of counted with βα counter 224 Ra, 226 Ra, 228 Th Vacuum & Membrane Radon removal Purification De-gassing Lucas Cells Assay of 222 Rn Reverse Osmosis conc. collection Purification liquid scintillator Assay Ion Exchange & Ultrafiltration Purification 19

20 The in-situ technique Target levels correspond to ~1 neutron/day. This is equivalent to ~ Tl decays/day or ~ Bi decays/day. Use these events to determine the levels of 232 Th and 238 U. Convert to actual levels in the D 2 O using the Monte Carlo. 20

21 NHITS of 208 Tl and 214 Bi events Low NHITS events with a tail extending out to ~45 NHITS. 214 Bi events These type of events from 232 Th and 238 U in the detector limit the low energy threshold. 208 Tl events 21

22 Isotropy of 208 Tl and 214 Bi events θ ij is the mean angle between pairs of hit PMTs, with respect to the event position. 208 Tl βγ events for these NHITS have a higher multiplicity than 214 Bi βγ events. θ ij is used to separate 214 Bi and 208 Tl events. 214 Bi events 208 Tl events ij run over hit PMTs θ ij 22

23 24 Na decay scheme A potential problem? perhaps a source? 2.75MeV 23

24 24 Na as a source 24 Na events have similar NHITS and θ ij distributions to 208 Tl and 214 Bi events. Containerless source. 24

25 24 Na as a source Super hot thorium source deployed in the D 2 O for ~20 hours to activate 24 Na. Super hot thorium source strength: MeV min -1 Giving ~ Na min -1 NHITS agreement very good. Demonstrates deutron photodisintegration cross section is modelled correctly. 24 Na decays neutrons 25

26 24 Na as a source 24 Na θ ij is ~1% lower for data than Monte Carlo. This contributes a systematic error to the Tl/Bi separation. 26

27 24 Na as a source Total 24 Na calculated from source strength and neutron event rate. T½=14.96 hours Number of 24 Na events observed calculated from fit. Ratio of observed events to total events, crucial to in-situ analysis, agrees with Monte Carlo to better than 10%. 27

28 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-So 2 oscillations are excluded by these results at >99.8% c.l. The 8 B n flux from the Sun is now measured to be in agreement with the predictions of Standard Solar Models. 28