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SNO II: Salt Strikes Back. Update from the Sudbury Neutrino Observatory. Joseph A. Formaggio University of Washington NuFACT’03. Our understanding of neutrinos has changed in light of new evidence: Neutrinos no longer massless particles (though mass is very small) - PowerPoint PPT Presentation
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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.
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