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Calibrating the SNO Detector Response Andre Hamer Los Alamos National Laboratory For the SNO Collaboration. Outline. The SNO Experiment Calibrating SNO The Calibration Devices Detector Response Studies Solar Neutrino Fluxes Measured by SNO + Systematic Uncertainties.

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Outline

CalibratingtheSNODetectorResponseAndre HamerLos Alamos National LaboratoryFor the SNO Collaboration


Outline

Outline

  • The SNO Experiment

  • Calibrating SNO

  • The Calibration Devices

  • Detector Response Studies

  • Solar Neutrino Fluxes Measured by SNO

    + Systematic Uncertainties


The solar neutrino problem

Solar Neutrinos

Figure by J. Bahcall

TheSolarNeutrinoProblem

Experimental Results

SAGE+GALLEX/GNO

Flux = 0.58 SSM

Homestake

Flux = 0.33 SSM

Kamiokande + Superkamiokande

Flux = 0.46 SSM

Do Neutrinos Oscillate ?


The sno detector

TheSNODetector

Nucl. Inst. and Meth. A449, p172 (2000)


Neutrino detection in sno

Neutral-Current (NC)

nx + d nx+ n + p

nx + e-nx + e-

Elastic Scattering (ES)

NeutrinoDetectioninSNO

Charged-Current (CC)

neOnly

BetterSpectralSensitivity

Weakdirectionalsensitivity1-1/3cos(q)

ne + d e- + p + p

nxEqual Sensitivity to all flavours

nxEnhanced Sensitivity for ne

Strong DirectionalSensitivity

Lower Statistics


The solar neutrino program

ne

CC

=

ne+ 0.154(nm+nt)

ES

ne

CC

=

(ne+nm+nt)

NC

The Solar Neutrino Program

Test for Flavour Change

Measure Total 8B Flux

Temporal Dependences

Spectral Distortions

Hep Flux


The experimental phases

ThisTalk

TheExperimentalPhases

I. Pure D2O

II. D2O+NaClAdditive

III. D2O + NCDs

(3He proportional counters)

CC & ES (EThreshold=6.75 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


Calibration in sno

CalibrationinSNO

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


Source deployment and manipulation

SourceDeploymentandManipulation

Umbilicals

Manipulation

Detector Interface

Radon/Light Barrier

Accuracy

< 2 cm single axis

~ 5 cm triple axis

Remote Operation/Interlocks

Stringent Cleanliness Requirements


The optical source

Wavelengths

337 nm, 365 nm,

386 nm, 420 nm,

500 nm, 620 nm

Dye Laser System

100’ Fibre

Optic

Pulse Rate

Up to 45 Hz

Pulse Width

600 ps

Adjustable Intensity

Neutral-Density

Filters

Diffuser Ball

TheOpticalSource


The short lived radioisotope sources

Nitrogen-16

Nearly Mono-energetic

6.13 MeV (66.2 %), 7.12 MeV (4.8 %)

Half-Life:7.13 sec.

Tagged by Beta

Nucl-ex/0109011

Lithium-8

Beta Spectrum

Central Endpoint Value (12.98 MeV)

Half-Life:0.838 sec.

Tagged by Alpha

Nucl-ex/0202024

TheShortLivedRadioisotopeSources


Radioisotope production

RadioisotopeProduction

DT Generator

Two Target Chambers

16O(n,p)16N 11B(n,a)8Li

MF Physics A320P 10^8 n/s


Radioisotope transport

RadioisotopeTransport

Transfer Length

Capillaries

Transport Streams

Flow Rates

Head Pressures

~220 feet

1/8” Teflon

CO2 (16N)

He+NaCl (8Li)

260 Atm-cc/sec

~95 psiA (16N)

~35 psiA(8Li)


The 16 n chamber

The16NChamber

BlocksBetas

Tagging Efficiency > 90 %

Decay Rate 1-300 Hz

Tunable via DT target position, DT n-output, Gas Flow


The 8 li chamber

The8LiChamber

Good Alpha Discrimination

Alpha Scintillation in Helium

~0.1 % N2 as wavelength shifter

Tagging Efficiency > 90 %

Decay Rate ~0.5 Hz


Outline

ThepTSource

Compact ion source/accelerator

DC proton beam (<30 keV)

High Purity ScT2 target (4 Ci T2)

Lifetime: 100 hours

3H(p,g)4He reaction 19.8 MeV g

  • rate: ~0.5 Hz neutron rate: < 1kHz

    Nucl. Instr. and Meth. A452, p 115 (2000).

TheEncapsulatedSources

Radioisotopes encased in acrylic

252Cf

232U (Thorium Chain)

226Ra(Uranium Chain)

neutrons

2.6 MeV g

2.4 MeV g


Optical analysis

OpticalAnalysis

D2O Attenuation

H2O Attenuation

PMTcalibrations, PMTangularresponse, lD20, lacrylic,lH2O


Energy scale with 16 n

EnergyScale with 16N

Cherenkov Timing

All PMT Hits

Tune PMT

Efficiency in

Monte Carlo

Prompt Hits

Optical Response

Cos Theta R

Event Radius


Energy response checks

Energy Response Checks

VerifyEnergyResponse

with 16N, 252Cf, 8Li, pT

  • Temporal Stability

  • Position Dependence

  • Energy Dependence

  • Resolution

Time

Energy

Position

Energy Scale Uncertainty: 1.4 %


Reconstruction response

ReconstructionResponse

Vertex from 16N and 8Li

Angular Resolution

N16

Important for ES

Extraction

Bias

Li8

N16

Resolution

Resolution: 16 cm vertex, 26.70 angular @ 5 MeV


Testing cuts

Testing Cuts

Low Level Cuts

High Level Cuts

Fractional Signal Loss

Mean angle between PMT hits

Number of Hits

Fraction of prompt hits


High energy g contamination

High Energy g Contamination

16N

n Data


High threshold d2o analysis

High Threshold D2O Analysis

Simulated Response

Evidence: neutrino oscillations

CC

NC

ES

Energy or Nhit

X 106 cm-2s-1

Fmt

Radius Cubed

Direction from Sun

Fe

Phys. Rev. Lett. 87 (2001) 071301


Systematic errors high threshold analysis

SystematicErrors:HighThresholdAnalysis

Error Source

Energy Scale

Energy Resolution

Energy Non-Linearity

Vertex Accuracy

Vertex Resolution

Angular Resolution

High Energy g‘s

Low Energy Bkg.

Instrumental Bkg.

Cut Acceptance

Trigger Efficiency

Livetime

Experimental Total

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

Calibrations used with MC

16N

16N, pT

16N, 8Li, pT

16N, 8Li

16N, 8Li

16N

16N

U/Th

16N, 8Li

16N, 8Li


Outline

Conclusions

SNO has developed unique devices and methods for calibrating its

detector response, establishing systematic uncertainties, and

understanding backgrounds.

We have presented SNO’s 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.


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