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
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).
1. The Solar Neutrino Problem
• Solar neutrinos provide a unique
opportunity to study physics beyond the
standard model.
L
• Huge flux:  
10
 2 1

6
.
5

10
cm
s

(13MeV )( 4D)
• Long baseline: 1 AU = 1.5x108 km
• Relatively low neutrino energy (~ MeV)
1. pp chain and Standard Solar
Model
p+p2H+e++e
[pp  ]
85%
p+e+p2H+e
[pep  ]
p+2H 3He+g
15%
3He+p4He+
e++e
[hep  ]
3He+4He7Be+g
0.02%
7Be+p8B+g
8B8Be*+e++
e
8Be*4He+4He
[8 B
]
e-7Li+e
7Li+p4He+4He
7Be+
[7Be  ]
Overall: 4p + 2e  4He + 2e +
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
Increasing
detection
energy
threshold
GALLEX :
 e 71Ga 
71
SAGE :
 e 71Ga 
71
Homestake :  e  37 Cl 
37
Super - K :
Ge e
Ge e
Ar e
 x e   x e
Ga ( e )
 0.58  0.05
SSM ( e )
Ga ( e )
 0.60  0.05
SSM ( e )
Cl ( e )
 0.34  0.03
SSM ( e )
SK ( x )
 0.4510.017
0.015
SSM ( e )
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
Speed of sound in solar interior
temperature Tc to
lower the predicted
flux, e.g. Fn(8B) T25
• BUT: Poor agreement
with other parameters
• SSM accurately
describes many
observations
1. Neutrino Oscillation
 mass eigenstates | i  (i=1,2,3)
flavor eigenstates | l  (l= e,
 l   Ul,i  i ,
i

In two flavor mixing

Probability of e transformation over a distance L
 cos

U
  sin
sin  

cos 


2
2
P ( e    ,L)  sin2 2 sin2 1.27 m [eV ] L[m]  ,
E [MeV]


2
2
2
where m  m1  m2
• Combination of
baseline/neutrino-energy
(L/E) probes different
regions in the (m2,tan2)
parameter space.
• Mikheyev-SmirnovWolfenstein (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
e  d  p p e
-
e
ed
Charged Current:
• Measurement of e spectrum
• Weak directionality: 1-0.340cos
NC
 x  d  p  n  x
x  e-  x  e -
p
x
x
d
Neutral Current:
• Measure total solar 8B  flux
• flux s(es(s(
ES
p
p
n
x
x
Elastic Scattering:
• Low statistics, strong directionality
• flux s(e ≈ 6s( ≈ 6s(
ee-
2. Neutrino Oscillation at SNO
• If no oscillation, solar neutrinos would be pure e.
• Measure the ratio,  CC ( )

e

e
 NC ( X )  e    
If e transform into other flavors, then

CC
(e )  
NC
( x )
• Alternatively, can also measure the ratio
 CC ( e )
e

ES
 ( X )  e  0.15 (    )
and detect transformation if
 CC ( e )   ES ( x )
3. Results from SNO
• Electron neutrino event recovered from the
Cherenkov radiation of the e-.
42o cone angle
e-
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 + g (6.25 MeV), s = 0.5 mb
• Low neutron capture and detection
efficiencies (en ~ 14% above threshold)
3. Phase I, PRL 87 (2001) 071301
• Measured CC(e) and compare with accurate
ES results from Super-K [PRL 86 (2001) 5651]
SK ES (1s)
3.3 s
1.6 s
Excludes pure esterile at 3.1 s
3. Phase I, PRL 89 (2002) 011301, 02
• All pure D2O data used
• Direct measurement of total 8B flux NC(X)
1.6 s

3. Main Results (Phase I)
A. Exclude  = 0 at 5.3s
0.05
0.09
e  1.76 0.05
(stat.)
(syst.) 10 6 cm2s 1
0.09
  
0.45
0.48
3.41
(stat.)
(syst.) 10 6 cm2s 1
0.45
0.45
B. SSM prediction verified (flux in units of
10-6 cm-2 s-1):
1.01
SSM (BP01)  5.05 0.81
Bahcall, Pinsonneault &
Basu (2001）ApJ, 555, 990
constrained
SNO
 5.09
0.44
0.43
(stat.)
0.46
0.43
(sy st.)
1.57
0.55
unconstrained
SNO
 6.42
(stat.)
(sy st.)
1.57
0.58
3. Phase II (Pure D2O + NaCl)
• 2 tonnes of NaCl added
• CC, ES, enhanced NCs
• n + 35Cl → 36Cl* + Sg’s (8.6 MeV), s = 44 b
• High neutron capture efficiency with higher
energy release (en ~ 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):
SNO
0.08
0.06
CC
 1.59 0.07
(stat) 0.08
(syst)

 2.21 0.26 (stat)  0.10 (syst)

 5.21  0.27(stat)  0.38(syst)
SNO
ES
SNO
NC
 0.31
1.01


5.05
Recall SSM (BP01)
0.81
3. Constraints on m2 and tan2
SNO Only
All Solar  experiments +
KamLAND
Best fit: m2 = 4.7x10-5,
tan2 = 0.43
Best 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 (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.
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. 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