Solar Neutrino Physics from SNO

Aksel HallinSNOLAB Opening

May 14, 2012

SNO physics: measure neutrinos that directly probe fusion reactions in the core of the sun

SNO sensitivity

Science in 1990:: Bahcall’s plot, neutrino oscillationsSNO made a direct measurement of the total

flux of solar neutrinos. Without SNO, we have the standard solar model predictions but no model independent measurement of the total solar neutrino flux.

Other experiments made measurements of electron neutrinos, and saw the significant depletion noted here, but were unable to distinguish between effects from an incorrect solar model and effects due to neutrino oscillations.

Ray Davis and John Bahcall had observed neutrino oscillations in the 70’s; but it was a model dependent observation that was suggestive but not definitive.

Pure D2OSalt Data

NCD Data “LETA” Salt+D2O

3PhaseAll Data

SNO’s Primary Measurements: Total Flux of All Neutrinos

ijijijij

ii

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μμμ

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UUUUUUUUU

U

sin,cos

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ilil U If neutrinos have mass:

)ELΔm.(θ)νP(ν eμ

222 271sin2sin

For three neutrinos:

Solar, Reactor Atmospheric

Using the oscillation framework:

For two neutrino oscillation in a vacuum: (valid approximation in many cases)

CP Violating Phase Reactor... Majorana Phases

Range defined for Dm12, Dm23

Maki-Nakagawa-Sakata-Pontecorvo matrix

(Double b decay only)

SNO measurements that constrain oscillations:

• Average survival probability, P.• Day/Night differences in survival probability• Energy dependence of survival probability

SNO 3 phase (2012)SNO D2O (2001)

SNO’s measurement and neutrino oscillation parameters:

ApproximateDaya Bay Result0.0235 +/- 0.0045

Some of the other SNO Measurements

PRD80 021001(2009): Muon PaperMeasured 1229 days, 514 event, 1.22+/- 0.09 Bartol flux prediction

Periodicity Paper: PRD72, 052010 (2005)No variations between 1d and 10 yearsExcept for eccentricity of orbit

Hep neutrino measurementPreliminary fit to allSNO data. Consistent withSSM 8e3/cm**2/s

+Nucleon decay, antineutrinos, spallation neutrons, …

Sudbury Neutrino Observatory

1700 tonnes Inner

Shielding H2O

1000 tonnes D2O

5300 tonnes Outer

Shield H2O

12 m Diameter Acrylic Vessel

Support Structure for 9500 PMTs, 60% coverage

Urylon Liner and

Radon Seal

Neutrino-Electron Scattering (ES)

Charged Current (CC)

Neutral Current (NC)

Phase I: Just D2O: neutron capture on deuterium• Simple detector configuration, clean measurement• Low neutron sensitivity• Poor discrimination between neutrons and electrons

Phase II: D2O + NaCl: neutron capture on Chlorine• Very good neutron sensitivity• Better neutron electron separation

• Phase III: D2O + 3He Proportional Counters• Good neutron sensitivity• Great neutron/electron separation

Three Phases of SNO: 3 NC reactions

Why three phases?

1. Additional information to separate NC and CC2. Completely different systematics, which allowed us to

check for consistency.3. Allowed us to “repeat” the measurement

Phase I (D2O)

Phase II(D2O+Salt)

“Beam On”

“Beam Off”

Advantages of (2-Phase) Low Threshold Analysis Breaking NC/CC Covariance

Observables

-position-time-Charge

Photomultiplier tube

NCD digitized data:

Neutrons

Alphas

Reconstruction

Reconstructed event-Vertex position-Electron direction-energy-Isotropy (reaction discriminator)-particle identification and counting in NCD’s

History of SNO saw a continuous progression of fitters- to improve resolution, Incorporate shadowing of the NCD’s, better incorporation of correlations, etc.

Cherenkov light and b14

) 43o

Charged particle, v > c/n

Hollow cone of emitted photons

Energy & Direction

ij

b14 b1 4b4

NEUTRINO EVENT DISPLAYED ON SNO COMPUTER SYSTEM

Controlling and Measuring Systematic Uncertainties

1. SNO spent a large fraction of the data acquisition time calibrating- which both determined the parameters for the MC and the systematic uncertainties.

2. In most cases, measured by careful comparison of calibration data with MC at various positions, times, energies, sources

3. The 3 single phase measurements were done with assumptions that often required increasing systematic uncertainties/thresholds.

4. The LETA analysis included a major re-evaluation of all systematic uncertainties from charge pedestals, source positions, fitter response, background measurements.

5. The 3Phase analysis included all the data, but used a high PMT –side energy threshold to stay away from backgrounds. It did include correlations between systematic effects in the various phases.

SNO Calibrations• Determine detector response (optical parameters and

time offsets): Dye-pumped laser and laser diffuser system.

• Absolute Quantum efficiency (16N source in center)• Neutron capture efficiency (252Cf, AmBe) sources

throughout volume• Position, direction and energy uncertainties• “Isotropy” (16N and 252Cf)

b’s from 8Li g’s from 16N and t(p, g)4He

252Cf neutrons

6.13 MeV19.8 MeV

Energy calibrated to ~1.5 %Throughout detector volume

Optical calibration at 5 wavelengths with “Laserball”

SNO Energy Calibrations

0.5% LETA

Background Reduction

Low Energy Threshold Analysis

LETA energy estimator includes both `prompt’ and `late’ light

12% more hits≈6% narrowing of resolution~60% reduction of internal backgrounds

LETA Cuts help reduce external backgrounds by ~80%

Fiducial Volume

βγβ

High charge early in timeExample:

Rayleigh Scatter

(it was good we fixed our pedestals…)

Low Energy Threshold AnalysisSystematic Uncertainties

• Nearly all systematic uncertainties from calibration data-MC• Upgrades to MC simulation yielded many reductions• Residual offsets used as corrections w/ add`l uncertainties• All uncertainties verified with multiple calibration sources

Volume-weighted uncertainties: Old: Phase I = ±1.2% Phase II = ±1.1% New: Phase I = ±0.6% Phase II = ±0.5% (about half Phase-correlated)

Low Energy Threshold AnalysisSystematic Uncertainties—Energy Scale

No correction With correction

16N calibration source6.13 MeV gs

Tested with: Independent 16N data, n capture events, Rn `spike’ events…

Central runs remove source positioning offsets,

MC upgrades reduce shifts

Fiducial volume uncertainties: Old: Phase I ~ ±3% Phase II ~ ±3% New: Phase I ~ ±1% Phase II ~ ±0.6%

Low Energy Threshold AnalysisSystematic Uncertainties—Position

Tested with: neutron captures, 8Li, outside-signal-box s

Old New

Low Energy Threshold AnalysisSystematic Uncertainties—Isotropy (b14)

MC simulation upgrades provide biggest source of improvementTests with muon `followers’, Am-Be source, Rn spikeb14 Scale uncertainties: Old: Phase I --- , Phase II = ±0.85% electrons, ±0.48% neutrons New: Phase I ±0.42%, Phase II =±0.24% electrons, +0.38%

-0.22% neutrons

PassFail

FailPass

FailFail

PassPass

NPF = e1(1-e2)Nb

NFP = (1-e1) e2Nb

NFF = (1-e1)(1-e2)Nb

NPP = e1e2Nb + Ns

NPMT= NPP – Ns = NFP * NPF /

NFF

Low Energy Threshold AnalysisPMT bg PDFs

Not enough CPUs to simulate sample of events Use data instead

In-time ratio In-time ratio

Early

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prob

abili

ty

Early

cha

rge

prob

abili

ty

(so fixing pedestals gave us a handle on these bkds…)

`Bifurcated’ analysis

Pulse Shape Analysis in NCDs (3 Phase)

1115 ± 79 neutrons

Signal Extraction: a multiparameter fit of the data to pdf’s describing the various signals and backgrounds; including correlations between phases, and a variety of systematic parameters. In 3 phase analysis, almost 60 parameters.

Three Phase Fit

Analysis techniques used by SNO

• Blind analysis• Independent analyses (at least two for every

publication)• Extended ML minimization against Monte Carlo and

analytic pdf’s of varying dimensionality.• Parameterizing and floating systematic functions• Markov chain monte carlo• Kernel estimation• Bifurcated analyses of backgrounds

And many, many arguments! Some of which were fun… at least afterwards.

SNO has published it’s final solar neutrino analyses.

A handful of remaining papers, such as the hep paper, the antineutrino paper and neutron backgrounds from cosmic rays atSNO depth will be finalized soon.

People of SNOB. Aharmim, Q.R. Ahmad, S.N. Ahmed, R.C. Allen, T.C. Andersen, J.D. Anglin, A.E. Anthony, N. Barros, J.C. Barton, E.W. Beier, A. Bellerive, B. Beltran, M. Bercovitch, M. Bergevin, J. Bigu, S.D. Biller, R.A. Black, I. Blevis, R.J. Boardman, J. Boger, E. Bonvin, K. Boudjemline, M.G. Boulay, M.G. Bowler, T.J. Bowles, S.J. Brice, M.C. Browne, G. Buehler, T.V. Bullard, T.H. Burritt, B. Cai, K. Cameron, J. Cameron, Y.D. Chan, D. Chauhan, M. Chen, H.H. Chen, X. Chen, M.C. Chon, B.T. Cleveland, E.T.H. Clifford, J.H.M. Cowan, D.F. Cowen, G.A. Cox, Y. Dai, X. Dai, F. Dalnoki-Veress, W.F. Davidson, H. Deng, J. Detwiler, M. DiMarco, P.J. Doe, G. Doucas, M.R. Dragowsky, P.-L. Drouin, C.A. Duba, F.A. Duncan, M. Dunford, J. Dunmore, E.D. Earle, S.R. Elliott, H.C. Evans, G.T. Ewan, J. Farine, H. Fergani, A.P. Ferraris, F. Fleurot, R.J. Ford, J.A. Formaggio, M.M. Fowler, K. Frame, E.D. Frank, W. Frati, N. Gagnon, J.V. Germani, S. Gil, A. Goldschmidt, J.TM. Goon, K. Graham, D.R. Grant, E. Guillian, S. Habib, R.L. Hahn, A.L. Hallin, E.D. Hallman, A. Hamer, A.A. Hamian, R.U. Haq, C.K. Hargrove, P.J. Harvey, R. Hazama, R. Heaton, K.M. Heeger, W.J. Heintzelman, J. Heise, R.L. Helmer, J.D. Hepburn, H. Heron, J. Hewett, A. Hime, C. Howard, M.A. Howe, M. Huang, J.G. Hykawy, M.C.P. Isaac, P. Jagam, B. Jamieson, N.A. Jelley, C. Jillings, G. Jonkmans, J. Karn, P.T. Keener, K.J. Keeter, K. Kirch, J.R. Klein, A.B. Knox, R.J. Komar, L.L. Kormos, M. Kos, R. Kouzes, C. Kraus, C.B. Krauss, T. Kutter, C.C.M. Kyba, J. Law, I.T. Lawson, M. Lay, H.W. Lee, K.T. Lesko, J.R. Leslie, I. Levine, J.C. Loach, W. Locke, M.M. Lowry, S. Luoma, J. Lyon, R. MacLellan, S. Majerus, H.B. Mak, J. Maneira, A.D. Marino, R. Martin, N. McCauley, A.B. McDonald, D.S. McDonald, K. McFarlane, S. McGee, G. McGregor, W. McLatchie, R. Meijer Drees, H. Mes, C. Mifflin, G.G. Miller, M.L. Miller, G. Milton, B.A. Moffat, B. Monreal, J. Monroe, M. Moorhead, B. Morissette, C.W. Nally, M.S. Neubauer, F.M. Newcomer, H.S. Ng, B.G. Nickel, A.J. Noble, A.J. Noble y, E.B. Norman, V.M. Novikov, N.S. Oblath, C.E. Okada, H.M. O'Keeffe, R.W. Ollerhead, M. Omori, M. O'Neill, G.D. Orebi Gann, J.L. Orrell, S.M. Oser, R.A. Ott, S.J.M. Peeters, A.W.P. Poon, G. Prior, T.J. Radcliffe, S.D. Reitzner, K. Rielage, A. Roberge, B.C. Robertson, R.G.H. Robertson, J.K. Rowley, V.L. Rusu, E. Saettler, K.K. Schaer, A. Schuelke, M.H. Schwendener, J.A. Secrest, S.R. Seibert, H. Seifert, M. Shatkay, O. Simard, J.J. Simpson, D. Sinclair, P. Skensved, A.R. Smith, M.W.E. Smith, T.J. Sonley, N. Starinsky, T.D. Steiger, R.G. Stokstad, L.C. Stonehill, R.S. Storey, B. Sur, R. Tafirout, N. Tagg, N.W. Tanner, R.K. Taplin, G. Tešic, M. Thorman, P. Thornewell P.T. Trent, N. Tolich, Y.I. Tserkovnyak, T. Tsui, C.D. Tunnell, R. Van Berg, R.G. Van de Water, B.A. VanDevender, C.J. Virtue, B.L. Wall, D. Waller, C.E. Waltham, H. Wan Chan Tseung, J.-X. Wang, D.L. Wark, N. West, J.B. Wilhelmy, J.F. Wilkerson, J. Wilson, J.R. Wilson, P. Wittich, J.M. Wouters, A. Wright, M. Yeh, M. Yeh, F. Zhang, K. Zuber