28-NOV-2003 @TMU

Solar Neutrino Results from
SNO Salt Phase
Yasuo Takeuchi

Kamioka Observatory,
ICRR, Univ. of Tokyo

SNO Detector
Neutron Event Separation
Calibration
Backgrounds
Results from Salt Phase
Future Plan
SNO web site: http://www.sno.phy.queensu.ca/

The Solar Neutrino Problem
Experiment
J. Bahcall

Exp/SSM・SAGE+GALLEX/GNO

0.58

・Homestake・Kamiokande+SuperK

0.33
0.46

・SNO pure D2O CC (June 2001)

0.35

SNO pure D2O NC (April 2002)

˜1

SNO CC vs NC implies flavor change, which can thenexplain other experimental results.
Precision phase (still need direct evidence of oscillation …)

Sudbury Neutrino Observatory (SNO)
Main goal:

Direct observation of solar neutrino
flavor change via inclusive appearance withhigh precision

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

SNO Detector

Sudbury Neutrino
Observatory

2km
under ground1000 tonnes D2O
Support Structure for 9500
PMTs (8-inch), 60% coverage
12 m Diameter Acrylic Vessel
1700 tonnes Inner
Shielding H2O
5300 tonnes Outer
Shield H2O
Urylon Liner andRadon Seal

NIM A449 (2000) 172

SNO during Construction

What We Measure
PMT Measurements-position-charge
-time

x10

2

1400
1200
1000
800
600
400
200
0
-20

0

20

40

60

80
100
PMT charge

Reconstructed Event-event vertex-event direction-energy-isotropyNeutrino Reactions in SNO
CCνe + d → p + p + e−

- Q = 1.445 MeV- good measurement of νe energy spectrum- some directional info ∝ (1 – 1/3 cosθ)- νe onlyNCν x + d → p + n +ν x

- Q = 2.22 MeV- measures total 8B ν flux from the Sun- equal cross section for all ν typesESν x + e− → ν x + e−

- low statistics- mainly sensitive to νe, some νµ and ντ- strong directional sensitivity

SNO s response to neutron events(solar NC signal)
1998

1999

2000

2001

2002

2003

Comm.

2004

2005

2006

NOW

Pure D2OSalt

3He Counters

added 2ton of NaCl

Pure D2O

Phase I
(pure D2O):

Phase II
(dissolved salt):

Neutron capture on D

Neutron capture on Cl

n+2H → 3H+ γ

n+35Cl → 36Cl+ ∑γ

Statistical separation(Energy, radius)

Statistical separation(Isotropy)

Single 6.25 MeV γ

Phase III
(3He n counters):n + 3He → p + t

Multiple γ s, 8.6 MeV

Independent
channelHigh CC-NC correlation Better CC-NC separation NC uncorrelated to CC

Nov. 1999˜Jul. 2001˜(Jan. 2004˜)Neutron Event Separation

Detecting Neutrons
・ Pure D2O: neutron capture on deuteronsγ'e−γ (6.25 MeV)

n
d

t*

Cherenkov
light

6.25 MeV
σ = 0.0005 bt
3H• Salt D2O: neutron capture on 35Clγ ‘s (8.6 MeV)

n
35Cl

2H+n

36Cl*

35Cl+n

8.6 MeVσ = 44 b

36Cl
36Cl

Advantages of NaCl for Neutron Detection• Higher capture cross section・ Higher energy release・ Many gammas

Neutron ‐ electron separation

Energy distribution (MC)Distribution of no. γ sStatistics(Salt phase)
Salt NC
Pure D2O NC
CC (electron)

4MeV

14MeV

1 2 3 4 5 6 7 8 9

Simulated Neutron Event
Pure D2O

look like electron events

Salt

more isotropic than electrons

Cherenkov light and β14
Reconstructedvertex positioniθij

Charged particle light conej

Define Harmonic Beta Parameters

Hit PMTs

β14 = β1 + 4β4Harmonic Beta Parameters– β14 gives better
separation power
than using <θij>
CC
NC

β14

<θij> (average< θ ij angle)>

Isotropy Calibration
・ Calibration sources show excellent agreement between
data and Monte Carlo.
Use β14 to distinguish neutrons and e-

Uncertainty of isotropy mean on fluxes = -3.4+3.1%(NC), -3.4+2.6%(CC)anti-correlated

Uncertainty on Neutrino Fluxes

Calibration

Calibration
・ Use detailed Monte Carlo tosimulate events・ Check simulation with large
number of calibrations:

Calibration

Simulates...

Pulsed Laser
16N
252Cf
8Li
AmBe
U & Th Sources
Radon Spike

337-620 nm optics
6.13 MeV γ (+4MeVβ)
neutrons<13 MeV β decay
4.4 MeV (γ ,n) source
214Bi & 208Tl (β,γ)
Rn backgrounds

Deck Clean Room (DCR)

glove box

sourceManipulator system

Tools for calibration

Laser ball

Manipulator demonstration@Queen s Univ.

glove box in DCR

Optical Calibration
・The PMT angular response andattenuation lengths of the media
are measured directly using
laser+diffuser ( laserball ).

・Attenuation for D2O and H2O, aswell as PMT angular response,
also measured in-situ using
radial scans of the laserball.

・Exhibit a change as a function oftime after salt was added to thedetector.

Vertex reconstruction of 16N events
Vertex resolution ~15 cm
Radial accuracy on neutrino flux
-3.0+3.5%(NC)-2.6+2.5%(CC)N2 gas
-2.6+2.9%(ES)activated by
DT n source

UNTAGGED
PMT
for tagdecaychamberplastic
scintillater

TAGGED

・

Energy response of thedetector determined from 16N
decay.

・

Mono-energetic γ at 6.13 MeV,
accompanied by tagged β
decay.

・

Provides check on the opticalproperties of the detector.

・Energy scale is changing

16N Energy (MeV)

Energy Response from 16N Calibration Source:1

˜1.2%

˜2.0%

Energy Response from 16N Calibration Source:2
Energy scale drift
・ HV drift
・ Gain drift
・ Threshold drift
・ Attenuation changes
・ Concentrator degradation

・

Radial, temporal, and rate dependencies well modeled by Monte Carlo.

Energy Response・

In addition to 16N (γ), additional
calibration sources are
employed to understand energy
response of the detector.
・ Muon followers (neutron)・ 252Cf (neutron)・ 8Li (β)
・ …

252Cf
8Li

16N

・

Excellent agreement!
Systematics dominated bysource uncertainties, opticalmodels, and radial/asymmetry
distributions

Energy Scale = + 1.1%

Energy Resolution = + 3.5%

Neutron Response・

Use neutron calibration sources(252Cf and AmBe) to determine
capture profile for neutrons.

・

252Cf decays by a emission or

acrylic cylinder(height 2.5cm, radius2.5cm)

252Cf source

spontaneous fission.
(3.768 + 0.005 neutrons/fission)・

Observe resulting γ cascade fromneutron capture on 35Cl.

・

γ s accompanying the fission andβ s emitted by daughter products
are removed using a timing cut.

・Monte Carlo agrees well withobserved distributions.

Radius (cm)Neutron Capture Efficiency in SNO
35Cl(n,γ)36Cl(no energy cut)(no energy cut)

Average Efficiency
39.9%
Te ≥ 5.5 MeV andRγ ≤ 550 cm
2H(n,γ)3H

Average Efficiency
14.4%

Radial Position of 252Cf Source, cm

Te ≥ 5.0 MeV andRγ ≤ 550 cm

Uncertainty of neutron capture efficiency on flux (Salt) = -2.5+2.7%(NC)Backgrounds

Backgrounds
・ Highly sensitive to any
γ above neutral current(2.2 MeV) threshold.

3.27 MeV β
2.445 MeV γ
2.615 MeV γ

UraniumThorium

Measuring U/Th
・ In-situ:
Low energy data

Ion exchange (224Ra,
226Ra)• MnOxMembrane degassing • HTiOCount daughter
product decays• MnOx• HTiO

Salt Added• Bottom of vessel• 2/3 way up• Top of vessel
Pure D2O

・ Ex-situ:

Radon Spike!

Old Backgrounds, New Technique:
Radon ̀Spikes
・ Controlled radon spike
added to D2O tomeasure behavior of
low-energy
backgrounds.
・ 80 Bq of Rn slowly
mixed in heavy water.

New Backgrounds
・ Salt and heightened neutron
sensitivity introduces
new/increased backgrounds
in salt phase.

Acrylic Vessel
D2O

H2O

‐ 24Na from neck of vessel.
‐ Cosmic rays
‐ Atmospheric neutrinos, Fission‐ External (α,n) reactions oncarbon and oxygen in acrylic
vessel・ Use radial profile toexplicitly fit for external
neutron, regardless ofsource.

(Reconstructed radius, cm/ 600)3

Summary of Backgrounds
SourceNo. Events

Deuteron photodisintegration

73.1 +24.0,-25.5

2H(α,α)pn

2.8 +/- 0.7

17,18 O(α,n)

1.4 +/- 0.9

Fission, atmospheric ν s

23.0 +/- 7.2

Terrestrial and reactor ν s

2.3 +/- 0.8

Neutrons from rock<1

24Na activation

8.4 +/- 2.3

Neutrons from CNO ν s

0.3 +/- 0.3

Total internal neutrons

111.3 +/- 25

Internal γ (fission, atm. ν)

5.2 +/- 1.3

16N decays< 2.5 (68% CL)

External-source neutrons (from fit)

84.5 +/- 34

Cherenkov events from β-γ decays<14.7 (68% CL)

AV events< 5.4 (68% CL)

Results from Salt PhaseSignal Extraction for Salt
(nucl-ex/0309004)
Data from July 26,
2001 to Oct. 10, 2002
254.2 live days
Blind analysis
performed
3055 candidate
events:1339.6 +63.8 -61.5 CC
1344.2 +69.8 -69.0 NC
170.3 +23.9 -20.1 ES

Angle to Sun
Isotropy
Kinetic EnergyFlux Measurements+0.06
Φcc = 1.59+0.08(stat)(syst)-0.07-0.08

Unconstrained Flux:ΦES = 2.21+0.31(stat) + 0.10 (syst)-0.26
ΦNC = 5.21 + 0.27 (stat) + 0.38 (syst)

Φcc = 1.70 + 0.07 (stat) +0.09(syst)-0.10
Constrained Flux:+0.15
ΦES = 2.13+0.29(stat)(syst)-0.28- 0.08

ΦNC = 4.90 + 0.24 (stat) +0.29(syst)-0.27* in units of 106 cm-2 s-1

Total Active 8B Fluxes
8B BPB01 SSM

NC Pure D2OConstrained
NC Salt
Unconstrained

5.05 (1+0.20-0.16)x 106 cm-2 s-1
5.09 (1±0.13)x 106 cm-2 s-1
5.21 (1±0.09)x 106 cm-2 s-1

・Consistent with pure D2O.
・Experimental error on 8B flux was reduced.

Oscillation Analysis: Only SNO

--90%
--95%
--99%
--99.73%

Before Salt

After Salt

Oscillation Analysis: Solar Global
Before Salt

--90%
--95%
--99%
--99.73%

After Salt

Oscillation Analysis: Solar + KamLAND
Solar global, after Salt

Solar global+KamLAND,
after Salt

--90%
--95%
--99%
--99.73%

LMA 2
LMA 1

LMA 2 only at > 99% CL

1-D Plots
Maximal mixing
rejected at 5.4 σ

LMA 1Results from SNO -- Salt Phase
Oscillation Parameters,
2-D joint 1-σ boundary< 1% probability of LMA 2

Marginalized 1-D 1-σerrorsMaximal mixing rejected
at 5.4 σAnalyses of energy spectrum & day/night with full Salt
data set is on going.

Future Plan

Salt Removal (Sept. ~ Oct., 2003)
・ Salt was removed using
a reverse osmosis unit,
which produces aconcentrated brine.
・ The target is for ˜1ppm
salt in the D2O after
multiple (3-4) passes
through the unit.
・ SNO will move to thethird phase of theexperiment.

Salt removal has been completed.

SNO Phase III (NCD Phase)¾ 3He Proportional Counters ( NC Detectors )40 Strings on 1-m grid
440 m total active lengthνx

Detection Principle
2H + ν

x → p + n + νx - 2.22 MeV

(NC)

PMT

3He + n → p + 3H + 0.76 MeV

Physics Motivation
Event-by-event separation. Measure NC
and CC in separate data streams.
Different systematic uncertainties
than neutron capture on NaCl.
NCD array removes neutrons from CC,
calibrates remainder. CC spectral shape.

NCDnWhy Event-by-Event?
Phase I
SourceEnergy Scale ¶Energy Resolution ¶Energy Non-linearity ¶Vertex Resolution ¶Vertex Accuracy
Angular Resolution
Internal Source p-d ¶External Source p-d ¶D2O Cherenkov ¶H2O Cherenkov
AV Cherenkov
PMT Cherenkov ¶Neutron CaptureΣ SystematicΣ StatisticalΣ Uncertainties¶ CC NC anti-correlation∆CC/CC (%)-4.2, +4.3
-0.9, +0.0
±0.1
±0.0
-2.8, +2.9
-0.2, +0.2
±0.0
±0.1
-0.1, +0.2
±0.0
±0.0
±0.1
±0.0

∆NC/NC (%)-6.2, +6.1
-0.0, +4.4
±0.4
±0.1
±1.8
-0.3, +0.3
-1.5, +1.6
-1.0, +1.0
-2.6, +1.2
-0.2, +0.4
-0.2, +0.2
-2.1, +1.6
-4.0, +3.6

-5.2, +5.2 -8.5, +9.1
-2.8, +3.4 -8.5, +8.6
7
12

Phase III
Projected∆NC/NC (%)
0.0
0.0
0.0
0.0
0.0
0.0
3.0
1.0
0.0
0.0
0.0
0.0
3.0

4.5
4
6

Current Status of the NCD Project
Milestones
Counter construction complete Done
Radio assays complete

April 2001

NCD in-situ background test

Sep 2000

Neutron Background Estimates
From radio assay:< 4.0% SSM
Schedule
Routine data taking+analysis

Ongoing

Training for NCD installation

Complete

Salt removal
Deployment of NCD array

Complete
Ongoing

NCD Phase Begins 04

Summary
・ SNO has measured total active 8B flux precisely, thenapply tight constraints on the oscillation parameters.
Total active 8B flux = 5.21 (1±0.09)x 106 cm-2 s-1(1D)・ Some new analyses with full Salt data set are on going.
・ Neutral Current Detectors are now under deployment.
・ SNO Phase-III (NCD) will start in January 2004.

Supplements

Uncertainties in Fluxes (%)
0
Energy scale
Resolution
Radial accuracy
Angular res.
Isotropy mean
Isotropy width
Radial E bias
Internal neutrons
Cher. bkds
AV events
Neutron capture
Total

1

2

3

4

5

6

7

8

CC uncert.
NC uncert.
ES uncert.

910(α,n) Reactions

Backgrounds

For the unconstrained fits…
Correlation coefficients:

Ratio:

CC, ES, and NC fluxes from Pure D2O Phase
Shape of 8B spectrum in CC and ES not constrained:

Standard (Ortiz et al.) shape of 8B spectrum in CC and ES:

Extracting Signals
Can use derived observables (R3, cosθsun, and E)
to produce pdfs.
EnergyDistribution

RadialDistribution(R3, RAV=1)
Solar
Direction
Distribution

Max. Likelihood fit for relative signal amplitudes

SNO Phase II (Salt Phase)¾ Advantages of NaCl: Signal Extraction
CC
ES
NC
EnergyDistribution

NC Shifted

RadialDistribution(R3, RAV=1)

NC Changed

Solar
Direction
Distribution

Unchanged

Isotropy
Distribution

All New
Covariances between Isotropy and Energy actually require 2D PDFs

Statistical Signal Separation (D2O
phase analysis)•Signal PDFs used for statistical separation
F CC ( r , E , cos θ sun )F ES ( r , E , cos θ sun )F NC ( r , E , cos θ sun )SNO response in event
radius, energy and direction
to solar neutrinos throughCC, ES, and NC reactions

Maximum Likelihood fit
for ν fluxes263.6
576.5

+49.5
+48.9

NC

300
200

Bkgd

0
0

(c)

500
400
300
CC
200
100

Bkgd

NC + bkgd
neutrons
ES

0
5

6

160

(a)

7

8

9

(b)

400

100

Events per 500 keV

ES

+26.4
+25.6

600

CC
NC + bkgd neutrons
ES
0.2

0.4

0.6

Events per 0.05 wide bin

500

CC 1967.7

+61.9
+60.9

Fiducial Volume

Events per 0.1 wide bin#EVENTS

Shape Constrained Signal Extraction Results(Pure D2O phase)

1
1.2
3(R/R AV)11

12 13→ 20
T eff (MeV)

140
120
100
80
60

CC

40

0.8

10

20

ES

NC + bkgd neutrons

Bkgd
0-1 -0.8 -0.6 -0.4 -0.2 -0 0.2 0.4 0.6 0.8 1
cos θsunExternal 24Na

The NaCl brine in theunderground buffertank was activatedby neutrons from therock wall. We
observed the decay of
24Na after the brine isinjected in the SNO
detector.

Injection
began

24Na Backgroundt1/2=14.95 hrs

CountsSalt Injected on
May 28, 2001

Injection
Ended

-200

-100

0

100

Time Since Salt Injection (hrs)200

Background Measurements in Salt Phase
Containerless source• A hot Th source is used to24Na

2.75 MeV
1.37 MeV
t1/2=14.95h

24Mg

photodisintegrate the deuteron.
The resulting neutrons activate the23Na nuclei in the salt
• Used to test the low energy
response of the detector, and to
calibrate the light isotropy
parameters used in the low energy
background in-situ analysis• Used to trace the water flow
pattern in the ex-situ assay ofradioactive backgrounds

Neutral Currents in the First Phase¾ Making the NC Measurement
BUT IF…!
• Flavor change occurs,
CC flux ~ 1/3 as large• Detector is clean enough,backgrounds are tolerable

Still hard because:• Need good measurement of
low energy radioactivity• Need to understand all sourcesof neutrons other than ν’s

SNO Phase II (Salt Phase)

Eliminate residual instrumentals
by requiring events to have
Cerenkov characteristics:
Narrow timing
Cerenkov hit pattern
Even with looser isotropy cut for salt
phase, preliminary upper limit on
residual contamination still
lower than a few events.

Coefficients(β14)hits
MeanLegendre
angle between
phototube

Challenges of NaCl: Backgrounds New (and Old)
Instrumental Background

Fraction of hits in a prompt time window
Fraction of hits in prompt time window