Evidence of Neutrino Oscillation from SNO

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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

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Outline

• The Solar Neutrino Problem
• (Brief) Descriptions of SNO
• Results from SNO
• Future (and present) plans for SNO
• Acknowledgement This presentation borrows
  heavily from SNO member, Dr Alan W.P. Poon (LBL).

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1. The Solar Neutrino Problem

• Solar neutrinos provide a unique opportunity to
  study physics beyond the standard model.
• Huge flux
• Long baseline 1 AU 1.5x108 km
• Relatively low neutrino energy ( MeV)

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1. pp chain and Standard Solar Model
pp?2Hene
pep?2Hne
pp n
pep n
p2H? 3Heg
85
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3Hep?4He ene
hep n
3He4He?7Beg
Overall 4p 2e ? 4He 2ne 26.7MeV
0.02
7Be e-?7Line 7Lip?4He4He
7Bep?8Bg 8B?8Beene 8Be?4He4He
7Be n
8B n
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Combining with detailed model of solar evolution,
we get the Standard Solar Model (SSM)
(CC)
(cm-2 s-1)
SNO(NC)
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1.Solar Neutrino Problem
Increasing detection energy threshold

• The discrepancy suggests either
• Solar models are incomplete and/or incorrect
• Neutrinos undergo flavor-changing transformation
  along the way from the Sun to Earth

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1. Astrophysical Solution to the Problem

• Reduce the solar core temperature Tc to lower the
  predicted flux, e.g. Fn(8B) ?T25
• BUT Poor agreement with other parameters
• SSM accurately describes many observations

Speed of sound in solar interior
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Neutrino Oscillation
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• Combination of baseline/neutrino-energy (L/E)
  probes different regions in the (Dm2,tan2q)
  parameter space.
• Mikheyev-Smirnov-Wolfenstein (MSW) effect
  resonance enhancement of the oscillation
  amplitude in dense matter (e.g. solar interior)

(Murayama 2003)
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2. The Sudbury Neutrino Observatory (SNO)
1000 tons D2O

• 2km underground in Sudbury, Canada
• 9456 20-cm PMTs in a 12m diameter vessel (56
  coverage)

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2. Neutrino reactions at SNO

• Charged Current
• Measurement of ne spectrum
• Weak directionality 1-0.340cosq

• Neutral Current
• Measure total solar 8B n flux
• flux s(ne)s(nm)s(nt)

• Elastic Scattering
• Low statistics, strong directionality
• flux s(ne) 6s(nm) 6s(nt)

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2. Neutrino Oscillation at SNO

• If no oscillation, solar neutrinos would be pure
  ne.
• Measure the ratio,
• If ne transform into other flavors, then
• Alternatively, can also measure the ratio
• and detect transformation if

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3. Results from SNO

• Electron neutrino event recovered from the
  Cherenkov radiation of the e-.

42o cone angle
e-
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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 D2O (Nov 99 May 01)
• Phase II Pure D2O NaCl (Jul 01 Sep 03)
• Phase III D2O 3He Proportional Counters (Nov
  03 ?)

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3. Phase I (Pure D2O)

• CC, ES, some NCs
• n 2H ? 3H g (6.25 MeV), s 0.5 mb
• Low neutron capture and detection efficiencies
  (en 14 above threshold)

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3. Phase I, PRL 87 (2001) 071301

• Measured fCC(ne) and compare with accurate ES
  results from Super-K PRL 86 (2001) 5651

SK ES (1s)
1.6 s
3.3 s
Excludes pure ne?nsterile at 3.1 s
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3. Phase I, PRL 89 (2002) 011301, 02

• All pure D2O data used
• Direct measurement of total 8B flux fNC(nX)

1.6 s
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3. Main Results (Phase I)

• Exclude fmn 0 at 5.3s
• SSM prediction verified (flux in units of 10-6
  cm-2 s-1)

Bahcall, Pinsonneault Basu (2001)ApJ, 555, 990
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3. Phase II (Pure D2O NaCl)

• 2 tonnes of NaCl added
• CC, ES, enhanced NCs
• n 35Cl ? 36Cl Sgs (8.6 MeV), s 44 b
• High neutron capture efficiency with higher
  energy release (en 40 above threshold)

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3. Phase II, nucl-ex/0309004

• Spectral distributions of the ES and CC events
  are not constrained to the standard 8B spectral
  shape.
• Measured total 8B flux (in units of 10-6 cm-2
  s-1)

Recall
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3. Constraints on Dm2 and tan2q
Best fit Dm2 4.7x10-5, tan2q 0.43
Best fit Dm2 6.5x10-5, tan2q 0.40
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4. Phase III (Pure D2O 3He)

• Arrays of 3He proportional counters (Neutral
  Current Detectors, NCD) inserted
• n 3He ? p 3H 760 keV (en 37)
• Motives
• CC, NC measured in separate data streams
• Different systematic uncertainties
• Search for direct evidence of MSW effect, from CC
  spectral shape distortion.

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4. Phase III (Pure D2O 3He)

• Nov 2003 ?
• 40 strings on 1-m grid
• 440m total active length.
• Installed by a small remote control submarine

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The SNO Collaboration
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 Queens 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

• 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