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Karsten M. Heeger Les Houches, June 19, 2001
Sudbury Neutrino Observatory
Results from the Sudbury Neutrino Observatory
Karsten M. Heeger
For the SNO Collaboration CENPA, Seattle
Karsten M. Heeger Les Houches, June 19, 2001
Sudbury Neutrino Observatory
Design and Physics Objectives
Detector Operations
Calibration and Detector Response
Data Analysis
First Results
Karsten M. Heeger Les Houches, June 19, 2001
SNO Collaboration
J. Boger, R. L Hahn, J.K. Rowley, M. YehBrookhaven National Laboratory
I. Blevis, F. Dalnoki-Veress, W. Davidson, J. Farine, D.R. Grant, C. K. Hargrove, I. Levine, K. McFarlane, C. Mifflin,
T. Noble, V.M. Novikov, M. O'Neill, M. Shatkay, D. Sinclair, N. StarinskyCarleton University
J. Bigu, J.H.M. Cowan, E. D. Hallman, R.U. Haq, J. Hewett, J.G. Hykawy, G. Jonkmans, 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, A. R.
Smith, A. Schülke, R. G. Stokstad.Lawrence Berkeley National Laboratory
T. J. Bowles, S. J. Brice, M. Dragowsky, M.M. Fowler, A. Goldschmidt, A. Hamer, A. Hime, K. Kirch, G.G. Miller,
J.B. Wilhelmy, J.M. Wouters. Los Alamos National Laboratory
E. Bonvin, M.G. Boulay, M. Chen, F.A. Duncan, E.D. Earle, H.C. Evans, G.T. Ewan, R.J. Ford, A.L. Hallin, P.J. Harvey, J.D. Hepburn, C. Jillings, H.W. Lee, J.R. Leslie, H.B. Mak, A.B. McDonald, W. McLatchie, B. Moffat, B.C.
Robertson, P. Skensved, B. Sur. Queen's University
S. Gil, J. Heise, R. Helmer, R.J. Komar, T. Kutter, C.W. Nally, H.S. Ng,Y. Tserkovnyak, C.E. Waltham.
University of British Columbia
T.C. Andersen, M.C. Chon, P. Jagam, J. Law, I.T. Lawson, R. W. Ollerhead, J. J. Simpson, N. Tagg, J.X. Wang
University of Guelph
J.C. Barton, S.Biller, R. Black, R. Boardman, M. Bowler, J. Cameron, B. Cleveland, X. Dai, G. Doucas, J. Dunmore, H. Fergani, A.P. Ferraris, K.Frame, H. Heron, C. Howard, N.A. Jelley, A.B. Knox, M. Lay, W. Locke, J. Lyon, S. Majerus, N.
McCaulay, G. McGregor, M. Moorhead, M. Omori, N.W. Tanner, R. Taplin, M. Thorman, P. Thornewell. P.T. Trent, D.L.Wark, N.
West, J. WilsonUniversity of Oxford
E. W. Beier, D. F. Cowen, E. D. Frank, W. Frati, W.J. Heintzelman, P.T. Keener, J. R. Klein, C.C.M. Kyba, D. S.
McDonald, M.S.Neubauer, F.M. Newcomer, S. Oser, V. Rusu, R. Van Berg, R.G. Van de Water, P. Wittich.
University of Pennsylvania
Q.R. Ahmad, M.C. Browne, T.V. Bullard, P.J. Doe, C.A. Duba, S.R. Elliott, R. Fardon, J.V. Germani, A.A. Hamian, R. Hazama,
K.M. Heeger, M. Howe, R. Meijer Drees, J.L. Orrell, R.G.H. Robertson, K. Schaffer, M.W.E. Smith, T.D. Steiger, J.F.
Wilkerson. University of Washington
R.G. Allen, G. Buhler, H.H. Chen*University of California, Irvine
Karsten M. Heeger Les Houches, June 19, 2001
Sudbury Neutrino Observatory
2092 m to Surface (6010 m w.e.)
17.8 m Diameter Support Structure for 9456 20 cm PMTs~55% coverage within 7 m
1000 Tonnes D2O
12 m Diameter Acrylic Vessel
1700 Tonnes Inner Shielding H2O
5300 Tonnes Outer Shield H2O
Urylon Liner and Radon Seal
Karsten M. Heeger Les Houches, June 19, 2001
Neutrino Detection in SNO
Neutrino Interactions in D2O and H2O and their Flavor Sensitivity
Charged-Current (CC) e only
e+de-+p+p Measurement of energy spectrumEthresh = 1.4 MeV
Elastic Scattering (ES) x, but enhanced for e
x+e-x+e- Strong directional sensitivity
Neutral-Current (NC) x
x+d x+n+p Measures total 8B flux from SunEthresh = 2.2 MeV
Karsten M. Heeger Les Houches, June 19, 2001
SNO Physics Program
Solar Neutrinos Search for flavor changeCC/ES, CC/NC
8B Total Flux (test of solar models) Spectral distortions Time Dependences
diurnalannualsolar cycle
Measurement of hep flux
Supernova watch, relic SN neutrinos
Antineutrinos
Atmospheric Neutrinos
Karsten M. Heeger Les Houches, June 19, 2001
SNO Run Sequence
I. Pure D2O CC, ESsome NCn+d t+ ... (E= 6.25 MeV, n~24%)
II. D2O+NaCl CC, ES (added salt) enhanced NC
n+35Cl 36Cl+ ∑(E ∑ = 8.6 MeV, n~45% above threshold)
III. D2O+NCDs Concurrent CC, NC, ES(3He proportional counters) n+3He p+t
event by event separation (n~37%)
Karsten M. Heeger Les Houches, June 19, 2001
SNO Phase II - Addition of Salt
SNO Phase II: D2O+NaCL• Runtime about 8 months• Enhances neutron capture efficiency:
n~83% (~45% above threshold)
May 28 - June 5, 2001• Salt introduced at bottom of detector• Addition of NaCL completed
Event Rate vs z Position During Addition of Salt
Karsten M. Heeger Les Houches, June 19, 2001
SNO Phase II - Physics with Salt
NC Salt (BP98)
• Enhanced NC sensitivity n~45% above threshold
• Systematic check of energy scaleE ∑ = 8.6 MeV
• NC and CC separation by event isotropy
Karsten M. Heeger Les Houches, June 19, 2001
Preparations for Phase III - Neutral Current Detectors
NCD ArrayNC Detection: n+3He p+tTotal Length: 775 mCounters: 292 (300)Vertical Strings: 96n capture efficiency: n~45%
Neutron Background Estimates from Radioassayuniform+near vessel: <4.4% SSM
Status of NCD ProjectFirst deployment of NCD into D2O Sep 2000Counter construction complete April 2001Electronics Commissioning Summer 2001DAQ partially completeAnalysis of cooldown dataDevelopment of pulse shape analysis techniques
Schedule Pre-deployment welding: Winter 2001Deployment of NCD array: Summer 2002
Karsten M. Heeger Les Houches, June 19, 2001
Calibration and Detector Response
Calibration TechniquesElectronics electronic pulsers, pulsed light sources
Optical Response pulsed laser at =337, 365, 386, 420, 500, and 620 nm, ~2 ns resolution
Energy response 16N 6.13 MeV , taggedp,t 19.8 MeV neutrons 6.25 MeV 8Li spectrum 13 MeV endpoint8B spectrum 15 MeV endpoint
Calibration Issues• Photon Generation, transport, and detection
• different media: D2O, acrylic, H2O, PMT
• attenuation, reflection, scattering
• Detector geometry• Detector status and conditions
Karsten M. Heeger Les Houches, June 19, 2001
Calibration Systems
Source Deployment• In two planes in D2O• One line in H2O (so far)• Positioning accuracy: ± 2-5 cm
H2O
D2O
Karsten M. Heeger Les Houches, June 19, 2001
Optical Response - Timing Residuals
Source at Center
Source at z=500 cm
Timing ResidualsDifference in time between hit and direct flight time from vertex
Event Energy Estimators
I. Prompt light with position and direction correction
II. Total light (Nhit)without position and direction correction
Karsten M. Heeger Les Houches, June 19, 2001
Time Since Last Hit Dependence
Effect• Variation in ADC pedestal with time since last hit (TSLH)• Variation in ADC slope with time since last hit (TSLH)
Observation Timing residuals depend on data rate
Software SolutionCalibrated out in reconstruction of neutrino data
Effect on Reconstruction
Karsten M. Heeger Les Houches, June 19, 2001
Event Reconstruction
Calibration Sources in D2O 16N ’s and 8Li ’s in H2O 16N ’s
AV
Nec
k
Vertex resolution: ~ 16 cm
Karsten M. Heeger Les Houches, June 19, 2001
Angular Resolution
Error in reconstructed event direction:
Resolution function: true angular resolution + multiple scattering of e-
Angular resolution: 26.7 º small effect on flux determination
θe =r u fit •
r u e
Karsten M. Heeger Les Houches, June 19, 2001
Optical Response: D2O and H2O Attenuation
D2O Attenuation Length: ~ 100 m
Karsten M. Heeger Les Houches, June 19, 2001
SNO Energy Response - Absolute Energy Scale
• established with triggered 16N (E= 6.13 MeV)• tested against 8Li,252Cf, and (p,t) source
Sources at Center
8Li13 MeV endpoint(n,) on 11B
(p,t)E=19.8 MeV
from 3H(p,)4He
252CfE= 6.25 MeVfrom n capture
Karsten M. Heeger Les Houches, June 19, 2001
SNO Energy Response - Spatial Dependence
• various 16N positions inside D2O • Monte-Carlo prediction tested against extended distribution of 6.25-MeV from 252Cf neutrons
more difficult to analyze passive neutron source
tagged neutron source under development
Karsten M. Heeger Les Houches, June 19, 2001
Temporal Dependence of Energy Scale
• use center 16N high voltage runs and compare data and Monte-Carlo• actual detector configurations are simulated: noise rate, working tubes
energy drift: 2.2 ± 0.2% year
cause of drift is under investigation
Karsten M. Heeger Les Houches, June 19, 2001
Data Taking and Live Time
Nov 2, 1999 Jan 15, 2001 240.9 live daysneutrino runtime
Karsten M. Heeger Les Houches, June 19, 2001
Detector Performance
Trigger Type Hardware Threshold Rate (Hz)Pulsed Trigger Zero Bias 5100 ns Coincidence 16 PMTs 820ns Coincidence 16 PMTS 0.02Energy sum ~150 p.e. 4Prescaled (1:1000) 11 PMTs 0.1
Trigger Rates and Thresholds in 2001
Instantaneous Trigger Rate ~ 15-18 HzData Trigger Rate ~ 6-8 HzHardware Threshold ~ 2 MeV
Channel threshold: ~ 0.25 photo-electronsMultiplicity trigger: 18 Nhit within 93 ns Trigger efficiency: 100% efficiency by 25 Nhit (~3 MeV)
Karsten M. Heeger Les Houches, June 19, 2001
Solar Neutrino Data Analysis
Run SelectionData Division
CalibrationMonte-Carlo Simulations
Instrumental Background RemovalReconstruction I
Instrumental Background RemovalReconstruction II
High Level Cuts
Energy Estimator (prompt light)Small Fiducial Volume
High ThresholdBackground Estimates
Signal Extraction Technique
Energy Estimator (total light)Variable Fiducial Volume
Lower ThresholdFit to the Backgrounds
Signal Extraction Technique
Karsten M. Heeger Les Houches, June 19, 2001
Data Flow & Instrumental Background Cuts
Data Flow
Analysis Step Events
Total Event Triggers355,320,964Neutrino Data Triggers 143,756,178Nhit30 6,372,899Instrumental Background 1,842,491Muon Followers 1,809,979High Level Cuts 956,535Fiducial Volume Cut 18,783Threshold Cut,Teff6.75 MeV 1169
Total EventsIn Final Data Set 1169
High Level Cuts: Reconstruction figures of meritIn-time lightEvent isotropy (ij)
Karsten M. Heeger Les Houches, June 19, 2001
Removal of Instrumental Background
Instrumental removal: Two independent methodsSignal loss: 0.4±0.3%within Rfit≤550 cm from 16N, 8Li, and the laser ballContamination: limits from bifurcated analyses and hand-scanning
Overlay of Cleaned Nhit spectra
Karsten M. Heeger Les Houches, June 19, 2001
Instrumental Backgrounds Neck Tubes Fired
Electronic Pickup
Karsten M. Heeger Les Houches, June 19, 2001
High Level Data Cuts
• Reconstruction Figures of Merit
• In-Time Light Fraction uses detailed PMT time distributions
• Event Isotropy Average angle between hit PMTs
Event Isotropy• Tests hypothesis of single-particle origin for each event• Discriminates between simple Cerenkov electron and multiple vertices
From triggered 16N, 8Li, and bifurcated analyses
Volume-weighted signal loss: 1.4 +0.7/-0.6% Residual instrumental contamination: < 0.2%
Karsten M. Heeger Les Houches, June 19, 2001
Reconstructed Neutrino Candidate Events
Characteristic R3 Distribution
60
40
20
0
1.51.00.5 (R/AV)
3
AVFV
Cleaned Neutrino DataR<=550 cm + High Level Cuts
Signal Monte-Carlo
40x10-3
30
20
10
0
1.51.00.5 (R/AV)
3
x1/2=1.007 ± 0.002
Signal PDF Fit
60
40
20
0
1.51.00.5
(R/AV)3
Cleaned Neutrino DataR<=550 cm + High Level Cuts
Fit
x1/2=0.981 ± 0.010
Fiducial Volume R≤550 cm chosento minimize backgrounds
Variable FV analysis fits backgroundsoutside the AV
Fit to the AV Position
Karsten M. Heeger Les Houches, June 19, 2001
Reconstructed Neutrino Candidate Events
Characteristic Solar Angle Distribution
50
40
30
20
10
0
-0.5 0.0 0.5 cos(
Sun)
Cleaned Neutrino Data<=550 + R cm High Level Cuts Fit
Neutrino Candidate EventsRfit550cmNhit≥65High Level Cuts
Fit based on Monte-Carlo distributions
Note: Can already extract with larger uncertainty CC and ES rate from fits to cos(Sun) distribution alone
Karsten M. Heeger Les Houches, June 19, 2001
Reconstructed Neutrino Candidate Events
Characteristic Energy Spectrum
60
50
40
30
20
10
0
130120110100908070Nhit
1 bin
180
Cleaned Neutrino DataR<=550 cm + High Level Cuts
Event Energy Estimators
Teff or Nhit
both are calibrated with 16N
volume weighted mean response: ~ 9 Nhit/MeV
Effective Kinetic Energy Teff
• effective kinetic energy, Teff, determined for each event in D2O• Teff corrected for time variable phenomena + position + direction
Karsten M. Heeger Les Houches, June 19, 2001
Principal Physics Backgrounds
Internal D2O Background 238U, 232Th
Acrylic Vessel 238U, 232Th
H2O 238U, 232Th
PMT -
High Energy
6000
4000
2000
0
3.02.52.01.51.00.50.0 (R/AV)^3
AV PSUP CC ES Neutrons
208Tl in AV 214Bi in H2O
NHITS > 45
6000
4000
2000
0
3.02.52.01.51.00.50.0 (R/AV)^3
AV PSUP CC ES Neutrons
208Tl in AV 214Bi in H2O
NHITS > 65
Analysis of Backgrounds
I. Estimate limits in background free region Rfit≤550 cm
II. Fit to backgrounds in variable fiducial volumes
Karsten M. Heeger Les Houches, June 19, 2001
D2O Backgrounds
Target Level• Equivalent of 7% SSM neutrons
Measurement Techniques• Radiochemical assays• In-situ Cerenkov measures
Status at or below target level
Karsten M. Heeger Les Houches, June 19, 2001
H2O Backgrounds
Target• Equivalent of 7% SSM neutrons
Measurement Technique• Radiochemical assay• Encapsulated sources• High radon runs
Status near or below target levels
Karsten M. Heeger Les Houches, June 19, 2001
Acrylic Vessel Backgrounds
Calibration Techniques• direct counting and NAA• encapsulated U, Th sources• direct observation:
Cerenkov light
AV Activity• Activities assayed to be < 10% of target level ~ 0.2 ppt U/Th
AV Construction• Every piece sampled and tested • Sample bonds tested
AV Blob: ~ 9 +20/-5 ± 3 g ‘Th’
Karsten M. Heeger Les Houches, June 19, 2001
PMT -
Monte-Carlo 16N Data
Characteristics • Strong Nhit dependence but small tails into Cerenkov signals
Determination Direct counting of materials, Monte-Carlo simulations Hot encapsulated U and Th Sources (bkgd < 0.1% within D2O) 16N ’s from calibration source
AVAV
FVFV
Karsten M. Heeger Les Houches, June 19, 2001
External -Ray Background
Outward going
Inward going
u.r
Determination empirical estimates from cavity measures direct observation 16N calibration ’s (bkgd < 0.8% in data set)
R3Outward OutwardInward
Origin • from PMT’s, rock wall
AV
Karsten M. Heeger Les Houches, June 19, 2001
Experimental Systematic Errors on Fluxes
Vertex Shift 3.1 3.3Vertex Resolution 0.7 0.4Angular Resolution 0.5 2.2
Live Time 0.1 0.1Trigger Efficiency 0.0 0.0Cut Acceptance +0.7/-0.6 +0.7/-0.6
Experimental Uncertainty +7.0/-6.2 +6.8/-5.7
Cross Section 3.0 0.5
Error Source CC Error (%) ES Error (%)
Energy Scale +6.1/-5.2 +5.4/-3.5Energy Resolution 0.5 0.3Energy Scale Non-Linearity 0.5 0.4
Residual Backgrounds (Rfit≤550 cm)Instrumental Background 0.1 -0.6/+0.0High Energy ’s -0.8/+0.0 -1.9/+0.0Low Energy Background -0.2/+0.0 -0.2/+0.0
Karsten M. Heeger Les Houches, June 19, 2001
Signal Extraction
Maximum-Likelihood Fit to Characteristic Distributions R3
cos(Sun) Neutron Energy Response
Energy Estimators Teff or Nhit
Fiducial Volume Rfit≤550 cm or variable FV R ≤650 cm
≤ 550cm
Variable FV
DataMC
Karsten M. Heeger Les Houches, June 19, 2001
First Solar Neutrino Results From SNO
Energy SpectrumTeff≥6.75 MeV and Rfit≤550 cmderived from fit without constraint on 8B shape
Solar Angle DistributionTeff≥6.75 MeV and Rfit≤550 cm
CC Spectrum Normalized to Predicted 8B SpectrumTeff≥6.75 MeV and Rfit≤550 cmWith correlated systematic errors
Karsten M. Heeger Les Houches, June 19, 2001
Neutrino Fluxes
Total 8B Flux from the Sun
SNO(8B) = 5.44 ± 0.99 x106 cm-2 s-1
SSM(8B) = 5.01 +1.01/-0.82 x106 cm-2 s-1 (BP2001)
Total flux in good agreement, CC is only component of total 8B flux
241-day Data from SNO
CCSNO(8B) = 1.75 ± 0.07 (stat.) +0.12/-0.11 (sys.) x106 cm-2 s-1
ESSNO(8B) = 2.39 ± 0.34 (stat.) +0.16/-0.14 (sys.) x106 cm-2 s-1
assuming 8B spectral shape, Teff < 6.75 MeV radiative corrections are not applied yet, will only decrease CC flux
CC Flux Relative to BP2001
RCC(8B) = 0.347 ± 0.029
Karsten M. Heeger Les Houches, June 19, 2001
CC/ES Ratio
CCES
=νe
νe +0.15(νμ +ντ )
ESSNO and ESSK
ESSNO (8B) = 2.39 ± 0.34 (stat.) +0.16/-0.14 (sys.) x106 cm-2 s-1
ES SK (8B) = 2.32 ± 0.03 (stat.) +0.08/-0.07 (sys.) x106 cm-2 s-1
good agreement
CCSNO/ESSK
CCSNO (8B) = 1.75 ± 0.07 (stat.) +0.12/-0.11 (sys.) ± 0.05 (theor.) x106 cm-2 s-1
ES SK (8B) = 2.32 ± 0.03 (stat.) +0.08/-0.07 (sys.) x106 cm-2 s-1
ESSK(8B) - CC
SNO(8B) = 0.57 ± 0.17 3.3 Probability of not being a downward fluctuation: 99.96%
*S. Fukuda, et al., hep-ex/0103032
Karsten M. Heeger Les Houches, June 19, 2001
Neutrino Flavor Composition of 8B Flux
Flavor content analysis of 8B solar neutrino flux from: SKES , SNO
CC
CC = e
ES = e + ,
SNOCC = 1.75 ± 0.13
SKES = 2.32 ± 0.09
Total active neutrino flux:
x = e + ,
= CC + (ES-CC )/
Evidence for oscillations: e
e = 1.75 ± 0.13
, = 3.69 ± 1.13
Karsten M. Heeger Les Houches, June 19, 2001
What About Sterile Neutrinos?
Comparing the Response of SNO and SK
Ref: Fogli, Lisi, et al, hep-ph/0102288, Villante et al., hep-ph/9807360
normalized rates over paired spectral regions are linearly related
SK Flux SNO Flux > 8.5 MeV > 6.75 MeV
SK8B(ES, >8.5) - SNO8B (CC, >6.75)= 0.54 ± 0.17
oscillations to sterile excluded at 3.1
Karsten M. Heeger Les Houches, June 19, 2001
Neutrino Oscillation Scenarios
To Sterile NeutrinosTo Active Neutrinos
• data exclude sterile neutrinos and “Just So2” parameter space• oscillations to active species
Karsten M. Heeger Les Houches, June 19, 2001
Cosmological Implications
• These results plus previous analyses suggest:
(me)2 < 10-3 eV2 or (me)2 < 10-3 eV2
• Limits on e mass give:
me < 2.8 eV
• Assuming the hypothesis of oscillations in atmospheric neutrinos:
(m)2 3 10-3 eV2
neutrino masses: 0.05 < m < 8.4 eV
mass fraction of neutrinos in the universe: 0.001 < < 0.18
e
Karsten M. Heeger Les Houches, June 19, 2001
Conclusions
• CC rate is low compared to the SSM prediction, and to the ES rates as measured by SNO and SK
• First direct indication of solar neutrinos of type other than e
• First measurement of the total flux of 8B neutrinos. It agrees wellwith SSM predictions: total(8B) = 5.44 ± 0.99 x106 cm-2 s-1
• Data exclude the “Just-So2” and sterile neutrino parameter spaces
• ∆m2 (e, ) < 10-3 eV2 0.05 < m < 8.4 eV
• Cosmological limit on neutrino mass: 0.001 < < 0.18
• Phase I of SNO experiment complete
e
Karsten M. Heeger Les Houches, June 19, 2001
First Results
http://www.sno.phy.queensu.ca
Karsten M. Heeger Les Houches, June 19, 2001
Additional Slides
Karsten M. Heeger Les Houches, June 19, 2001
Muon Analysis
Karsten M. Heeger Les Houches, June 19, 2001
Neutrino Event
Karsten M. Heeger Les Houches, June 19, 2001
Oscillation Scenarios and SNO
SNO
Ratio of measured 8B flux relative to BP2000:
RCCSNO=0.346 0.014 (stat.) 0.020 (sys.) 0.010 (theor.)
RESSNO= 0.529 0.073 (stat.) 0.035 (sys.) 0.014 (theor.)
From Bahcall, Krastev, and Smirnovhep-ph/0103179
Neutrino oscillation models with maximal mixing are not compatible
Data exclude “Just So2” parameters at ∆m2=6x10-12 eV2