Evidence of Neutrino Oscillation from SNO

Chun Shing Jason PunDepartment of Physics

The University of Hong Kong

Presented at the HKU Neutrino Workshop28 November, 2003

Outline1. 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).

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)

1210105.6)4)(13(

scmDMeV

L

7Be+p8B+8B8Be*+e++e

8Be*4He+4He

1. pp chain and Standard Solar Model

p+p2H+e++e p+e+p2H+e

p+2H 3He+

3He+4He7Be+

7Be+ e-7Li+e

7Li+p4He+4He

3He+p4He+ e++e

85% 15%

0.02%

[pp ] [pep ]

[hep ]

[7Be ][8B ]

Overall: 4p + 2e 4He + 2e + 26.7MeV

Combining with detailed model of solar evolution, we get the Standard Solar Model (SSM)

(cm

-2 s

-

1)

(CC)

SNO(NC)

1.Solar Neutrino Problem

GALLEX: e71Ga 71Ge e

Ga (e )

SSM (e )0.580.05

SAGE : e71Ga 71Ge e

Ga (e )

SSM (e )0.600.05

Homestake : e37 Cl 37 Are

Cl (e )

SSM (e )0.340.03

Super -K : x e x eSK (x )

SSM (e )0.451 0.015

0.017

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

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

1. Neutrino Oscillation mass eigenstates | i (i=1,2,3) flavor eigenstates | l (l= e,

l Ul ,ii i ,

In two flavor mixing

U cos sin sin cos

Probability of e transformation over a distance L

P (e ,L)sin2 2 sin2 1.27 m2[eV

2] L[m]

E [MeV]

,

where m 2 m12 m2

2

May also have resonance enhancement of theoscillation amplitude in dense matter (e.g. solarinterior) Mikheyev-Smirnov-Wolfenstein effect

• Combination of baseline/neutrino-energy (L/E) probes different regions in the (m2,tan2) parameter space.

• Mikheyev-Smirnov-Wolfenstein (MSW) effect: resonance enhancement of the oscillation amplitude in dense matter (e.g. solar interior)

(Murayama 2003)

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)

2. Neutrino reactions at SNO

CC-epd e p

NCxx

npd

ES -- ee x x

e-

d

p

p

e

Charged Current: • Measurement of e spectrum• Weak directionality: 1-0.340cos

Neutral Current: • Measure total solar 8B flux• flux e

Elastic Scattering: • Low statistics, strong directionality• fluxe≈ ≈

d p

n

xx

xx

e-

e-

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

e

eNC

eCC

)(

)(

X

CC (e ) NC (x )

)()(

)(

0.15e

eES

CC

X

e

)()( xe ESCC

3. Results from SNO• Electron neutrino event recovered from the

Cherenkov radiation of the e-.

e-

42o cone angle

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 – ?)

3. Phase I (Pure D2O)

• CC, ES, some NCs

• n + 2H → 3H + (6.25 MeV), = 0.5 mb

• Low neutron capture and detection efficiencies (n ~ 14% above threshold)

3.0

2.5

2.0

1.5

1.0SNO CC SNO ES

SK ES Flux (1 )

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 esterile at 3.1

3. Phase I, PRL 89 (2002) 011301, 02 • All pure D2O data used

• Direct measurement of total 8B flux NC(X)

1.6

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):

e 1.76 0.05

0.05(stat.) 0.09

0.09(syst.)106 cm 2s 1

3.410.45

0.45(stat.) 0.48

0.45(syst.)106 cm 2s 1

SSM (BP01) 5.05 1.01

0.81

SNOconstrained 5.09 0.44

0.43(stat.)

0.46

0.43(syst.)

SNOunconstrained 6.42 1.57

1.57(stat.)

0.55

0.58(syst.)

Bahcall, Pinsonneault & Basu (2001 ） ApJ, 555, 990

3. Phase II (Pure D2O + NaCl)

• 2 tonnes of NaCl added

• CC, ES, enhanced NCs

• n + 35Cl → 36Cl* + ’s (8.6 MeV), = 44 b

• High neutron capture efficiency with higher energy release (n ~ 40% above threshold)

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):

0.38(syst)0.27(stat)5.21

(syst) 0.10(stat)2.21

(syst)(stat)1.59

0.26

0.31

0.08

0.06

0.07

0.08

SNONC

SNOES

SNOCC

SSM (BP01) 5.05 1.01

0.81Recall

SNO Only

All Solar experiments +KamLAND

3. Constraints on m2 and tan2

Best fit: m2 = 4.7x10-5,

tan2 = 0.43Best fit: m2 = 6.5x10-5,

tan2 = 0.40

4. Phase III (Pure D2O + 3He)

• Arrays of 3He proportional counters (Neutral Current Detectors, NCD) inserted

• n + 3He → p + 3H + 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.

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

The SNO Collaboration

T. Kutter, C.W. Nally, S.M. Oser, C.E. WalthamUniversity of British Columbia

J. Boger, R.L. Hahn, R. Lange, M. YehBrookhaven 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. WallerCarleton 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. StokstadLawrence 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. WoutersLos 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. WarkRutherford Laboratory and University of Sussex

R.L. HelmerTRIUMF

A.E. Anthony, J.C. Hall, J.R. KleinUniversity 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