Ryan Martin,Queen’s University, Kingston, ON,

Canada8th January 2007- EPFL

The

The SNO CollaborationThe SNO Collaboration

Canada:Canada: Queen’s, Carleton, Guelph, Laurentian, University of British Columbia, TRIUMFQueen’s, Carleton, Guelph, Laurentian, University of British Columbia, TRIUMF

USA:USA: University of Pennsylvania, Los Alamos National Lab, Lawrence Berkley National Lab, University of University of Pennsylvania, Los Alamos National Lab, Lawrence Berkley National Lab, University of

Washington, Brookhaven National Lab, University of Texas, University of Louisiana, Indiana University Washington, Brookhaven National Lab, University of Texas, University of Louisiana, Indiana University South BendSouth Bend

UK:UK: Oxford UniversityOxford University

Portugal:Portugal: Lisbon Technical InstituteLisbon Technical Institute

OutlineOutline

Solar NeutrinosSolar NeutrinosThe Solar Neutrino ProblemThe Solar Neutrino ProblemNeutrino OscillationsNeutrino OscillationsThe Sudbury Neutrino ObservatoryThe Sudbury Neutrino ObservatoryOverview of the salt phaseOverview of the salt phaseThe NCD phaseThe NCD phaseSNOLAB, SNO+ and the futureSNOLAB, SNO+ and the future

Solar NeutrinosSolar Neutrinos Neutrinos are Neutrinos are

created in the created in the fusion reactions fusion reactions that power the Sunthat power the Sun

SNO is sensitive to SNO is sensitive to 88B neutrinos from B neutrinos from the p-p reaction the p-p reaction chain in the Sun chain in the Sun (>7MeV)(>7MeV)

pep neutrino flux pep neutrino flux has the smallest has the smallest uncertaintyuncertainty

The Solar Neutrino ProblemThe Solar Neutrino Problem

Detection of solar neutrinos first proposed Detection of solar neutrinos first proposed by Bahcall by Bahcall

Homestake experiment (Ray Davis) shows Homestake experiment (Ray Davis) shows first signs of solar neutrino deficit first signs of solar neutrino deficit

Until 2001, other experiments (SAGE, Until 2001, other experiments (SAGE, GALLEX) also see a solar neutrino deficit GALLEX) also see a solar neutrino deficit

Experimental evidence for the “solution” Experimental evidence for the “solution” provided by Super Kamiokande in 1998 provided by Super Kamiokande in 1998 (atmospheric neutrino oscillations)(atmospheric neutrino oscillations)

Neutrino OscillationsNeutrino Oscillations

Vacuum Oscillations (two flavours):Vacuum Oscillations (two flavours):

e

First proposed by Pontecorvo First proposed by Pontecorvo Neutrinos are quantum states, flavour and energy Neutrinos are quantum states, flavour and energy

eigenbasis are differenteigenbasis are different The PMNS matrix:The PMNS matrix:

The Solar Survival ProbabilityThe Solar Survival Probability

The survival The survival probability is energy probability is energy dependent due to the dependent due to the MSW effect (yet to be MSW effect (yet to be observed observed experimentally)experimentally)

SNO’s energy window SNO’s energy window not well positioned for not well positioned for observing MSWobserving MSW

The Situation before SNOThe Situation before SNO

Long standing deficit of electron flavour Long standing deficit of electron flavour neutrinos coming from the Sunneutrinos coming from the Sun

Need for an experiment that can measure Need for an experiment that can measure the total flux of solar neutrinos and verify the total flux of solar neutrinos and verify flavour-conversionflavour-conversion

The energy spectrum of solar neutrinos is The energy spectrum of solar neutrinos is yet unmeasuredyet unmeasured

The SNO DetectorThe SNO Detector Heavy Water (DHeavy Water (D22O) O)

Cherenkov detectorCherenkov detector 2km underground 2km underground

(6000mwe) in active (6000mwe) in active nickel minenickel mine

12m diameter Acrylic 12m diameter Acrylic Vessel (AV)Vessel (AV)

9000 PMTs on 18m 9000 PMTs on 18m diameter geodesic diameter geodesic structure (PSUP)structure (PSUP)

Surrounded by ultra-pure Surrounded by ultra-pure light water to shield from light water to shield from rockrock

The INCO mine and the clean labThe INCO mine and the clean lab

The Heavy Water reactionsThe Heavy Water reactions SNO is sensitive to three SNO is sensitive to three

different neutrino different neutrino reactions in Heavy Water:reactions in Heavy Water: Charged Current (CC):Charged Current (CC):

Only electron flavourOnly electron flavour Strong Energy CorrelationStrong Energy Correlation

Neutral Current (NC):Neutral Current (NC): All flavoursAll flavours Neutron capture on D Neutron capture on D

releases gamma that releases gamma that compton scatters electroncompton scatters electron

Elastic Scattering (ES):Elastic Scattering (ES): Mostly electron flavourMostly electron flavour Strong directional Strong directional

sensitivity, low statisticssensitivity, low statistics

The Three Phases of SNOThe Three Phases of SNO

Phase I: Pure DPhase I: Pure D2200 Measurement of all three reactions, but NC signal can only be Measurement of all three reactions, but NC signal can only be

extracted with “Energy Constrained” fitextracted with “Energy Constrained” fit Phase II: Salt (NaCl)Phase II: Salt (NaCl)

Neutron capture cross-section increased as well as energy Neutron capture cross-section increased as well as energy released from capture (2.5 gammas on average)released from capture (2.5 gammas on average)

The increase in isotropy of Cherenkov light from NC significantly The increase in isotropy of Cherenkov light from NC significantly increases the statistical separation between CC and NC (energy increases the statistical separation between CC and NC (energy unconstrained)unconstrained)

Phase III: The Neutral Current DetectorsPhase III: The Neutral Current Detectors Designed to independently measure the NC fluxDesigned to independently measure the NC flux Addition of 40 Addition of 40 33He proportional counters to count neutronsHe proportional counters to count neutrons Ended November 28Ended November 28thth 2006 ! 2006 !

SNO CalibrationSNO Calibration

About 20% of SNO time About 20% of SNO time is devoted to calibrationsis devoted to calibrations

A manipulator system A manipulator system allows for various sources allows for various sources to be moved along x-y-z to be moved along x-y-z in the detector:in the detector: Laser Ball (optical and Laser Ball (optical and

reconstruction)reconstruction) 1616N (energy)-tagged N (energy)-tagged

gammagamma 252252Cf (neutron detection Cf (neutron detection

efficiency)-fissionefficiency)-fission

SNO Monte-CarloSNO Monte-Carlo

The detector is fully The detector is fully modeled by Monte modeled by Monte Carlo (SNOMAN)Carlo (SNOMAN)

The Monte Carlo is The Monte Carlo is extensively tested with extensively tested with calibration datacalibration data

Monte Carlo verification Monte Carlo verification then allows for an then allows for an accurate estimate of accurate estimate of systematicssystematics

Basic Data Acquisition and Basic Data Acquisition and Cleaning in Salt PhaseCleaning in Salt Phase

Triggered events are recorded (timing and Triggered events are recorded (timing and position of PMTs that fired)position of PMTs that fired)

Low level data cleaning (instrumental Low level data cleaning (instrumental background, pathological events)background, pathological events)

Event reconstruction (position and Event reconstruction (position and direction of Cherenkov cone)direction of Cherenkov cone)

Observables calculated (Event energy)Observables calculated (Event energy)High level data cleaning (fiducial volume, High level data cleaning (fiducial volume,

Cherenkov characteristics)Cherenkov characteristics)

Signal Extraction in Salt PhaseSignal Extraction in Salt Phase

The signal extraction is performed with an extended maximum log-The signal extraction is performed with an extended maximum log-likelihood fitlikelihood fit

Probability Density Functions (pdfs) are generated for each Probability Density Functions (pdfs) are generated for each observable and signal (by Monte Carlo)observable and signal (by Monte Carlo)

Observable in salt phase:Observable in salt phase: Event directionEvent direction IsotropyIsotropy Radial PositionRadial Position EnergyEnergy

Signals and Backgrounds in salt phase:Signals and Backgrounds in salt phase: NC, CC, ES (signals!)NC, CC, ES (signals!) External neutronsExternal neutrons Internal neutrons (indistinguishable from NC)Internal neutrons (indistinguishable from NC)

Cos(Cos(θθsunsun))

Best handle on ES signalBest handle on ES signal Slight sensitivity to CCSlight sensitivity to CC

ββ1414 (Isotropy parameter) (Isotropy parameter)

NC signal is more isotropic and this observable NC signal is more isotropic and this observable places the strongest constraint on itplaces the strongest constraint on it

Radial DistributionRadial Distribution

Extracting external neutron backgroundsExtracting external neutron backgrounds Acrylic Vessel (AV) acts as a neutron sink on internal Acrylic Vessel (AV) acts as a neutron sink on internal

neutronsneutrons

EnergyEnergy

Reconstructed energy of the event is based on the number of hit Reconstructed energy of the event is based on the number of hit PMTsPMTs

Not constraining the CC energy shape allows one to measure it!Not constraining the CC energy shape allows one to measure it!

Results from Salt PhaseResults from Salt Phase

Energy SpectrumTotal Flux

Mixing Parameters:

-Δm2= (8 ± 0.5) x10-5 eV2

-θ = (33.9 ± 2.3)°

(With KAMLAND data!)

The Neutral Current Detectors The Neutral Current Detectors (NCDs)(NCDs)

NeutronAlpha

NCD observables: EnergyNCD observables: Energy ADC charge of NCD ADC charge of NCD

pulses is converted into pulses is converted into energy spectrum (scaled energy spectrum (scaled from from 210 210 Po peak)Po peak)

An “energy fit” can be An “energy fit” can be performed to extract performed to extract neutron signal:neutron signal: Do not know the Do not know the

background shapebackground shape Have to limit possible Have to limit possible

shapes under the neutron shapes under the neutron peakpeak

QGF PSAQGF PSA Pulse Shape Analysis (PSA): the idea to use Pulse Shape Analysis (PSA): the idea to use

pulse shapes to discriminate between neutrons pulse shapes to discriminate between neutrons and alphasand alphas

Queen’s Grid Fitter (QGF): a library of neutrons Queen’s Grid Fitter (QGF): a library of neutrons and alpha pulses is created from calibration and and alpha pulses is created from calibration and 44He data:He data: Data pulses are fit and the best neutron and best Data pulses are fit and the best neutron and best

alpha chi-squared are determinedalpha chi-squared are determined Currently, used as a cut (good neutron, bad alpha), Currently, used as a cut (good neutron, bad alpha),

before doing energy fitbefore doing energy fit Future (?), could be used as a pdf together with Future (?), could be used as a pdf together with

energyenergy

Results from QGF (used as a data-Results from QGF (used as a data-cleaning cut)cleaning cut)

When used as a 2D-When used as a 2D-cut:cut: 76% of neutrons pass 76% of neutrons pass 16% of alphas pass 16% of alphas pass 32% of WE pass 32% of WE pass

Signal/Background Signal/Background improves by factor of improves by factor of 55

The Future of SNOThe Future of SNO

After 7 years of successful data-taking, SNO is After 7 years of successful data-taking, SNO is currently being dismantledcurrently being dismantled

In the near future, publication of NCD resultsIn the near future, publication of NCD results In the long(er) term, combined analysis of the In the long(er) term, combined analysis of the

three phasesthree phases The NCDs are currently being “un-deployed”, in The NCDs are currently being “un-deployed”, in

preparation for the Heavy Water extractionpreparation for the Heavy Water extraction SNO has demonstrated the INCO site to be a SNO has demonstrated the INCO site to be a

good candidate for future low background good candidate for future low background experimentsexperiments

The SNO space is being expanded into a international low The SNO space is being expanded into a international low background facility for experiments on:background facility for experiments on: Direct Dark Matter DetectionDirect Dark Matter Detection Neutrino-less Double Beta DecayNeutrino-less Double Beta Decay Geo-NeutrinosGeo-Neutrinos Low-Energy Solar NeutrinosLow-Energy Solar Neutrinos

SNO+SNO+

The only thing that we don’t own is the The only thing that we don’t own is the heavy water!heavy water!

Why not keep using everything else?!Why not keep using everything else?!SNO+: Filling the Acrylic Vessel with liquid SNO+: Filling the Acrylic Vessel with liquid

scintillator scintillator Can use the PMT and most of the Can use the PMT and most of the

electronics already in placeelectronics already in place

SNO+ PhysicsSNO+ Physics

Low energy solar neutrinos (pep), can test Low energy solar neutrinos (pep), can test MSW effect on spectrumMSW effect on spectrum

Geo neutrinos (more events than Geo neutrinos (more events than KAMLAND)KAMLAND)

Reactor neutrinos (medium baseline)Reactor neutrinos (medium baseline)Could dope the scintillator with double-Could dope the scintillator with double-

beta decay isotopes (SNO++, kiloton beta decay isotopes (SNO++, kiloton experiment!)experiment!)

SummarySummary

SNO has shown that the solar model prediction SNO has shown that the solar model prediction was correct after allwas correct after all

Strong constraints are now placed on the solar Strong constraints are now placed on the solar mixing anglemixing angle

The MSW effect still remains to be observed The MSW effect still remains to be observed (spectrum or day-night effect)(spectrum or day-night effect)

The techniques for maintaining a clean The techniques for maintaining a clean underground lab are now well developedunderground lab are now well developed

Bright future for the subterranean part of Bright future for the subterranean part of Sudbury!Sudbury!

The End!The End!