SNO II:SNO II:Salt Strikes BackSalt Strikes Back

Joseph A. FormaggioUniversity of Washington

NuFACT’03

Update from the Update from the Sudbury Neutrino Sudbury Neutrino

ObservatoryObservatory

Beyond a Reasonable Doubt…

• Our understanding of neutrinos has changed in light of new evidence:

• Neutrinos no longer massless particles (though mass is very small)

• Experimental evidence from three different phenomena:

• Solar• Atmospheric• Accelerator• Reactor

• Data supports the interpretation that neutrinos oscillate.

Murayama

Solar Neutrino Experiments

Chlorine flux = 34% SSMGallium flux = 57% SSMSuper-K flux = 47% SSM

EXPERIMENTAL RESULTS

Need to measure x sloar flux, independently of e or solar model

The SNO The SNO ExperimentExperiment

Mapping the Sun with ’s

• Neutrinos from the sun allow a direct window into the nuclear solar processes.

• Each process has unique energy spectrum

• Only electron neutrinos are produced

• SNO sensitive to 8B neutrinos

Light Element Fusion Reactions

p + p 2H + e+ + e p + e- + p 2H + e

2H + p 3He +

3He + 4He 7Be +

7Be + e- 7Li + +e

7Li + p +

3He + 3He 4He + 2p

99.75% 0.25%

85% ~15%

0.02%15.07%

~10-5%

7Be + p 8B +

8B 8Be* + e+ + e

3He + p 4He + e+ +e

The SNO CollaborationG. Milton, B. Sur

Atomic Energy of Canada Ltd., Chalk River Laboratories

S. Gil, J. Heise, R.J. Komar, T. Kutter, C.W. Nally, H.S. Ng,Y.I. Tserkovnyak, C.E. WalthamUniversity of British Columbia

J. Boger, R.L Hahn, J.K. Rowley, M. YehBrookhaven National Laboratory

R.C. Allen, G. Bühler, H.H. Chen*

University of California, Irvine 

I. Blevis, F. Dalnoki-Veress, D.R. Grant, C.K. Hargrove,I. Levine, K. McFarlane, C. Mifflin, V.M. Novikov, M. O'Neill,

M. Shatkay, D. Sinclair, N. StarinskyCarleton University

 T.C. Andersen, P. Jagam, J. Law, I.T. Lawson, R.W. Ollerhead,

J.J. Simpson, N. Tagg, J.-X. WangUniversity of Guelph

J. Bigu, J.H.M. Cowan, J. Farine, E.D. Hallman, R.U. Haq,J. Hewett, J.G. Hykawy, G. Jonkmans, S. Luoma, 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, S.S.E Rosendahl,

A. Schülke, A.R. Smith, R.G. StokstadLawrence Berkeley National Laboratory

M.G. Boulay, T.J. Bowles, S.J. Brice, M.R. Dragowsky,M.M. Fowler, A.S. Hamer*, A. Hime, G.G. Miller,R.G. Van de Water, J.B. Wilhelmy, J.M. Wouters

Los Alamos National Laboratory

J.D. Anglin, M. Bercovitch, W.F. Davidson, R.S. Storey*

National Research Council of Canada

J.C. Barton, S. Biller, R.A. Black, R.J. Boardman, M.G. Bowler,J. Cameron, B.T. Cleveland, X. Dai, G. Doucas, J.A. Dunmore,

H. Fergani, A.P. Ferrarris, K. Frame, N. Gagnon, H. Heron, N.A. Jelley, A.B. Knox, M. Lay, W. Locke, J. Lyon, S. Majerus, G. McGregor,

M. Moorhead, M. Omori, C.J. Sims, N.W. Tanner, R.K. Taplin,M.Thorman, P.M. Thornewell, P.T. Trent, N. West, J.R. Wilson

University of Oxford

E.W. Beier, D.F. Cowen, M. Dunford, E.D. Frank, W. Frati,W.J. Heintzelman, P.T. Keener, J.R. Klein, C.C.M. Kyba, N. McCauley, D.S. McDonald, M.S. Neubauer, F.M. Newcomer, S.M. Oser, V.L Rusu,

S. Spreitzer, R. Van Berg, P. WittichUniversity of Pennsylvania

 R. Kouzes

Princeton University

E. Bonvin, M. Chen, E.T.H. Clifford, F.A. Duncan, E.D. Earle,H.C. Evans, G.T. Ewan, R.J. Ford, K. Graham, A.L. Hallin,

W.B. Handler, P.J. Harvey, J.D. Hepburn, C. Jillings, H.W. Lee,J.R. Leslie, H.B. Mak, J. Maneira, A.B. McDonald, B.A. Moffat,

T.J. Radcliffe, B.C. Robertson, P. SkensvedQueen’s University

D.L. WarkRutherford Appleton Laboratory, University of Sussex

R.L. Helmer, A.J. NobleTRIUMF

Q.R. Ahmad, M.C. Browne, T.V. Bullard, G.A. Cox, P.J. Doe,C.A. Duba, S.R. Elliott, J.A. Formaggio, J.V. Germani,

A.A. Hamian, R. Hazama, K.M. Heeger, K. Kazkaz, J. Manor, R. Meijer Drees, J.L. Orrell, R.G.H. Robertson, K.K. Schaffer,M.W.E. Smith, T.D. Steiger, L.C. Stonehill, J.F. Wilkerson

University of Washington

Somewhere in the Depths of Canada...

Sudbury Neutrino Observatory

2092 m to Surface (6010 m w.e.)

PMT Support Structure, 17.8 m9456 20 cm PMTs~55% coverage within 7 m

1000 Tonnes D2O

Acrylic Vessel, 12 m diameter

1700 Tonnes H2O, Inner Shield

5300 Tonnes H2O, Outer Shield

Urylon Liner and Radon Seal

Unique Signatures

Charged-Current (CC)e+d e-+p+pEthresh = 1.4 MeV

e only

Elastic Scattering (ES)x+e- x+e-

x, but enhanced for e

Neutral-Current (NC) x+d x+n+p Ethresh = 2.2 MeVx

Results from Pure D2O

• Measurement of 8B flux from the sun.

• Final flux numbers:

0 1 2 3 4 5 60

1

2

3

4

5

6

7

8

)-2 s-2 cm6 (10e

SNONC

SSMNC

SNOCC

SNOES

NCSNO

*= 5.09

8BSSM

*= 5.05 +1.01- 0.81

+0.44 +0.46- 0.43 -0.43

* in units of 106 cm-2 s-1

SNO Phase II - Salt

Enhanced NC sensitivity n~55% above thresholdn+35Cl 36Cl+ ∑

Systematic check of energy scaleE ∑ = 8.6 MeV

NC and CC separation by event isotropy

NC sensitivity n~14.2% above thresholdn+2H 3H+

Energy near thresholdE = 6.25 MeV

NC and CC separation by energy, radial, and directional distributions

D2O Salt

Advantages of Salt

• Neutrons capturing on 35Cl provide much higher neutron energy above threshold.

• Gamma cascade changes the angular profile.

• Higher capture efficiency

Same Measurement, Different Systematics

n

36Cl*35Cl 36Cl

Steps to a Signal

Calibrations

• Optics• Energy• Neutron Capture

Backgrounds

• Internal photo-disintegration• PMT -• External neutrons and other sources

Signal Extraction

• Charged current (CC)• Neutral Current (NC)• Elastic Scattering (ES)

Sources of Calibration

• Use detailed Monte Carlo to simulate events

• Check simulation with large number of calibrations:

Calibration

Pulsed Laser16N252Cf8LiAmBeU & Th SourcesRadon Spike

Simulates...

337-620 nm optics6.13 MeV neutrons<13 MeV decay4.4 MeV ,n) source 214Bi & 208Tl (,)Rn backgrounds

Optical Calibration

• The PMT angular response and attenuation lengths of the media are measured directly using laser+diffuser (“laserball”).

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

• Exhibit a change as a function of time after salt was added to the detector.

16N Calibration Source

• Energy response of the detector determined from 16N decay.

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

• Provides check on the optical properties of the detector.

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

16N

Energy Response

• In addition to 16N, additional calibration sources are employed to understand energy response of the detector.

• Muon followers• 252Cf• 8Li• 24Na

• Systematics dominated by source uncertainties, optical models, and radial/asymmetry distributions

Energy Scale = + 1.1%*

252Cf8Li

Energy Resolution = + 3.5%*

*Preliminary

Neutron Response

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

• 252Cf decays by emission or spontaneous fission.

• Observe resulting cascade from neutron capture on 35Cl.

• Monte Carlo agrees well with observed distributions.

Neutrons/fission = 3.7676 + 0.0047

Neutron Efficiency

Salt Preliminary

• Capture efficiency increase by 4-fold in comparison to pure D2O phase.

• Systematics include:• source position• energy response• source strength• modeling

• Less than 3% total systematic uncertainty on capture.

Backgrounds

Calibrations

• Optics• Energy• Neutron Capture

Backgrounds

• Internal photo-disintegration• PMT -• External backgrounds and other sources

Signal Extraction

• Charged current (CC)• Neutral Current (NC)• Elastic Scattering (ES)

3.27 MeV MeV

Uranium

An Ultraclean Environment

• Highly sensitive to any above neutral current (2.2 MeV) threshold.

• Sensitive to 238U and 232Th decay chains

“I will show you fear in a handful of dust.”-- T.S. Eliot

Thorium

2.615 MeV

U / Th and Other Backgrounds

Other Backgrounds

• Fission from possible U and Cf contamination

• Atmospheric neutrinos• 24Na from the vessel• 13C(,n) 16O from acrylic

• activation from radon embedded on the surface of the acrylic vessel.

• Measured from neutron radial profile and internal e+e- high-energy gamma conversion from 16O.

• Salt provides unique window of sensitivity to external neutrons.

Uranium and Thorium

• Two methods:• In-situ:

• Low Energy Data

• Separate 208Tl and 214Bi based on event isotropy

• Ex-situ:• Ion exchange (224Ra, 226Ra)

• Membrane degassing

• Count daughter product decays

• Preliminary salt measurements yield background levels at par with what was measured in D2O

Steps to a Signal

Calibrations

• Optics• Energy• Neutron Capture

Backgrounds

• Internal photo-disintegration• PMT -• External Neutrons and other backgrounds

Signal Extraction

• Charged current (CC)• Neutral Current (NC)• Elastic Scattering (ES)

NC E higher Less Rad. Sep.

DirectionalityUnchanged

Isotropy Separation

EnergyR3

cossun ij

Variables: E, R3, cossun, ij

UnconstrainedUnconstrained

88B Shape ConstrainedB Shape Constrained

Changes in Signal Extraction

• Based on data taken from May 27, 2001 to October 10, 2002.

• Total 254 live days of neutrino data.

• Previous analysis used energy, radial, and solar angle distribution to separate events.

• Introduction of salt moves neutron energy higher (but disrupts radial separation).

• New statistical separation using event isotropy, allowing both energy dependent and independent analyses.

Fit Result Uncertainties (Monte-Carlo)

10%5.3%3.8%R,sun,Iso

10%4.6%3.3%E,R,sun,Iso

10%6.3%4.2%E,R,sun

10%8.6%3.4%E,R,sun

ES Stat. Error

NC Stat. Error

CC Stat. Error

Variables

D2O results

SimulatedSalt PhaseResults

Published D2O energy-unconstrained statistical error was 24%

Simulations assume 1 yr of data with central values andcuts from D2O phase results

What’s Inside Pandora’s Box?

Day – Night

Contours (%)

Projected SNO Assuming D2O

NC Result Probability

Contours

De Holanda,Smirnovhep-ph/0212270

Coming Soon...Coming Soon...

SNO III:SNO III:

Return of the Return of the NeutronNeutron

SNO Phase IIIThe Neutral Current Detectors

Physics Motivation

Event-by-event separation. Measure NC and CC in separate data streams.

Different systematic uncertainties than neutron capture on NaCl.

NCD array as a neutron absorber.

Detection Principle

2H + x p + n + x -2.22 MeV (NC)

3He + n p + 3H

x

n

Array of 3He counters

40 Strings on 1-m grid

398 m total active length

NCD

PMT

Counters

• Ultraclean nickel counters of varying length, connected as “string”.

• Mixture of 3He (85%) and CF4

(15%).

• Anchored to the bottom of the acrylic vessel.

• Radioassayed and polished to reduce U and Th backgrounds.

The Remotely Operated Vehicle

• A remote controlled submarine will be used to deploy the NCDs in the acrylic vessel.

• The bottom end of the NCD string will be pulled to the floor of the acrylic vessel directly below the neck with a pulley.

• The ROV will then move the bottom end of the string along the floor of the acrylic vessel to its anchor point and anchor it.

Future Solar Physics

• Salt Phase:

• More precise measurements of CC/NC ratio, due to increased sensitivity to neutrons.

• Ability to extract solar flux with and without assumptions regarding the energy spectrum.

• Final systematics and backgrounds currently being evaluated.

• NCD Phase:

• Event-by-event separation of charged current and neutral current events.

• Model-independent extraction of charged current and neutral current flux.

• Begin deployment of counters in October.

Deployws.mov

ROV Training

Using Angular Information

• Use semi energy-independent variable 14 to separate neutrons from electrons via angular distributions.

• Allows one to reconstruct the energy profile of NC and CC events w/o use of energy constraint.

• Powerful check on the spectral shape of 8B

Monte Carlo

Monte Carlo

SNO during Construction

Masses and Mixings

F o r a 3 n e u t r i n o s c e n a r i o t h e l e p t o nm i x i n g m a t r i x ( M a k i - N a k a g a w a - S a k a t a -P o n t e c o r v o ) , w h i c h r e l a t e s m a s s e i g e n -s t a t e s t o w e a k o r f l a v o r e i g e n s t a t e s , i s :

e

U e 1 U e 2 U e 3

U 1 U 2 U 3

U 1 U 2 U 3

1

2

3

O s c i l l a t i o n e x p e r i m e n t s y i e l d m a s s s q u a r e dd i f f e r e n c e :

m 1 22 m 1

2 m 2

2

m 2 32 m 2

2 m 3

2

m 1 32 m 1

2 m 3

2

Pee ~ 1-sin2(2) sin2(1.27m2 L / E)

• Physics:m2 & sin2(2)

• Experiment:Distance (L) & Energy (E)

eee

Three Pieces

• For a full understanding of neutrino properties, it is necessary to determine:• The mixing parameters and phases

• The neutrino masses

• The physics governing mass

e µ

m1m2

m3m1

m 2m3

hierarchical degenerate

Higgs Field

Precision measurements!

Signal Extraction

CC 1967.7 +61.9 -60.9

+26.4 +25.6ES 263.6 +49.5 -48.9NC 576.5

Summary of Backgrounds

Background Salt Preliminary Pure D2O

External Cerenkov 5 + 5 25 + 12 -10

D2O Cerenkov 2 + 1 20 + 13 -6

Internal Photodisintigration 100 + 20 44 + 9External Photodisintigration 100 + 30 27 + 8Other sources 50 + 30 7 + 3

Detection

Electrons emit Čerenkov light, which is detected by the PMTs.

e

Neutrons are captured on 35Cl nuclei, which then emit a number of ’s

Comptonscatter

e'The ’s produce electrons through Compton scattering, or, less commonly, pair production or photoelectric absorption.

Distribution of no. ’s

(= 8.6 MeV)‘sn

36Cl*35Cl 36Cl

or on deuterium nuclei, as in the pure D2Ophase: n + d t + 6.25MeV (single )

Status

• All the NCDs are underground.

• The 156 NCDs that will be deployed have been identified.

• Pre-deployment welding is in progress.

• The DAQ is operational and has been taking data from complete unwelded strings of NCDs underground.

• All of the electronics are underground and operational.

• The current estimated deployment date is October 2003, subject to removal of salt.

What is changing? Why?

• Combination of both attenuation length and reflectors changing over time.

• Change in optics accounts for why there was a large drop in energy response.

• Attenuation length change correlated with change in water chemistry

• Reflectors consistent with both a sudden drop in response, as well as a gradual decay.

• Possible causes: petal degradation, temperature change

•Prediction from attenuation

•16N measured energy

Radon Spike

• Further aim at understanding backgrounds to lower energy threshold.

• Required to understand the detector uniformity and low energy tails.

• Injection of 50 ml of solution at 25 grid points in vessel

• 2.2 million Rn atoms/liter

16N Calibration Source

• Energy response of the detector determined from 16N decay.

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

• Provides check on the optical properties of the detector.

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