Calibrating the SNO Detector Response Andre Hamer Los Alamos National Laboratory For the SNO Collaboration

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Calibrating the SNO DetectorResponseAndre
HamerLos Alamos National LaboratoryFor the SNO
Collaboration
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Outline

• The SNO Experiment
• Calibrating SNO
• The Calibration Devices
• Detector Response Studies
• Solar Neutrino Fluxes Measured by SNO
• Systematic
  Uncertainties

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The Solar Neutrino Problem

• Experimental Results
• SAGEGALLEX/GNO
• Flux 0.58 SSM
• Homestake
• Flux 0.33 SSM
• Kamiokande Superkamiokande
• Flux 0.46 SSM

Do Neutrinos Oscillate ?
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The SNO Detector
Nucl. Inst. and Meth. A449, p172 (2000)
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Neutrino Detection in SNO
Charged-Current (CC)
ne Only Better Spectral Sensitivity Weak
directional sensitivity 1-1/3cos(q)
ne d e- p p
nx Equal Sensitivity to all flavours
nx Enhanced Sensitivity for ne Strong Directional
Sensitivity Lower Statistics
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The Solar Neutrino Program

• Test for Flavour Change
• Measure Total 8B Flux
• Temporal Dependences
• Spectral Distortions
• Hep Flux

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The Experimental Phases

• I. Pure D2O
• II. D2O NaCl Additive
• III. D2O NCDs
• (3He proportional counters)

• CC ES (EThreshold6.75 MeV)
• Add NC (Lower EThreshold)
• Enhanced NC Sensitivity
• NC/CC separation by event
• isotropy
• Event by event separation
• Improved Spectral Sensitivity

n ? d ? t ? g ? e? (Eg 6.25 MeV)
n ? 35Cl ? 36Cl ? ?g ? e? (E?g 8.6 MeV)
n ? 3He ? p ? t
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Calibration in SNO

• Primary Calibrations
• Electronics and PMT
• Optics Constants
• Energy Scale and Stability
• Verification of Response
• Energy Response
• Reconstruction Response
• Neutron Capture Response
• Characterizing Backgrounds
• Data Reduction
• High/Low Energy Background Estimates

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Source Deployment and Manipulation
Umbilicals
Manipulation
Detector Interface
Radon/Light Barrier
Accuracy lt 2 cm single axis 5 cm triple
axis Remote Operation/Interlocks Stringent
Cleanliness Requirements
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The Optical Source
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The Short Lived RadioisotopeSources

• Nitrogen-16
• Nearly Mono-energetic
• 6.13 MeV (66.2 ), 7.12 MeV (4.8 )
• Half-Life7.13 sec.
• Tagged by Beta
• Nucl-ex/0109011
• Lithium-8
• Beta Spectrum
• Central Endpoint Value (12.98 MeV)
• Half-Life0.838 sec.
• Tagged by Alpha
• Nucl-ex/0202024

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Radioisotope Production
DT Generator
Two Target Chambers
16O(n,p)16N 11B(n,a)8Li
MF Physics A320P 108 n/s
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Radioisotope Transport
Transfer Length Capillaries Transport
Streams Flow Rates Head Pressures
220 feet 1/8 Teflon CO2 (16N) HeNaCl (8Li) 260
Atm-cc/sec 95 psiA (16N) 35 psiA(8Li)
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The 16N Chamber
Blocks Betas Tagging Efficiency gt 90 Decay Rate
1-300 Hz Tunable via DT target position, DT
n-output, Gas Flow
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The 8Li Chamber
Good Alpha Discrimination
Alpha Scintillation in Helium 0.1 N2 as
wavelength shifter Tagging Efficiency gt 90
Decay Rate 0.5 Hz
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The pT Source
The Encapsulated Sources
Radioisotopes encased in acrylic 252Cf
232U (Thorium Chain) 226Ra(Uranium Chain)
neutrons
2.6 MeV g
2.4 MeV g
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Optical Analysis
D2O Attenuation
H2O Attenuation
PMT calibrations, PMT angular response, lD20,
lacrylic,lH2O
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Energy Scale with 16N
Cherenkov Timing
All PMT Hits
Tune PMT Efficiency in Monte Carlo
Prompt Hits
Optical Response
Cos Theta R
Event Radius
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Energy Response Checks
Time

• Verify Energy Response
• with 16N, 252Cf, 8Li, pT
• Temporal Stability
• Position Dependence
• Energy Dependence
• Resolution

Energy
Position
Energy Scale Uncertainty 1.4
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Reconstruction Response
Vertex from 16N and 8Li
Angular Resolution
N16
Important for ES Extraction
Bias
Li8
N16
Resolution
Resolution 16 cm vertex, 26.70 angular _at_ 5 MeV
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Testing Cuts
High Level Cuts
Low Level Cuts
Fractional Signal Loss
Mean angle between PMT hits
Fraction of prompt hits
Number of Hits
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High Energy g Contamination
16N
n Data
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High Threshold D2O Analysis
Evidence neutrino oscillations
Simulated Response
CC NC ES
Energy or Nhit
X 106 cm-2s-1
Fmt
Radius Cubed
Direction from Sun
Fe
Phys. Rev. Lett. 87 (2001) 071301
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Systematic Errors High Threshold Analysis

Error Source Energy Scale Energy
Resolution Energy Non-Linearity Vertex
Accuracy Vertex Resolution Angular
Resolution High Energy gs Low Energy
Bkg. Instrumental Bkg. Cut Acceptance Trigger
Efficiency Livetime Experimental Total
Calibrations used with MC 16N 16N, pT 16N,
8Li, pT 16N, 8Li 16N, 8Li 16N 16N U/Th 16N,
8Li 16N, 8Li
CC Error () -5.2,6.1 /-0.5 /-0.5 /-3.1 /-0
.7 /-0.5 -0.8,0.0 -0.2,0.0 -0.2,0.0 -0.6,0.7
0.0 /-0.1 -6.2,7.0
ES Error () -3.5,5.4 /-0.3 /-0.4 /-3.3 /-0
.4 /-2.2 -1.9,0.0 -0.2,0.0 -0.6,0.0 -0.6,0.7
0.0 /-0.1 -5.7,6.8
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Conclusions
SNO has developed unique devices and methods for
calibrating its detector response, establishing
systematic uncertainties, and understanding
backgrounds. We have presented SNOs initial
high threshold D2O analysis.
Outlook
Ongoing analysis is focused on lowering the
analysis threshold for the pure D2O Phase and
calibrating the Salt Phase of the
Experiment. This necessitates a greater emphasis
on neutron response and low energy backgrounds
studies. Low threshold analysis progressing well.