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Report on the Third and Final Phase of SNO - Physics and Astronomy

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ong>Reportong> on the Third and FinalPhase of SNOR.G. Hamish RobertsonUniversity of WashingtonforThe Sudbury Neutrino Observatory CollaborationNeutrinos 2008, Christchurch NZ, May 2008


SNO6000 mweoverburden1000 tonnes D 2 O12 m DiameterAcrylic Vessel1700 tonnes InnerShield H 2 OSupport Structurefor 9500 PMTs,60% coverage5300 tonnes OuterShield H 2 OImage courtesy National Geographic3 Reactions:ν x+ e − → ν x+ e −ν e+ d → p + p + e −ν x+ d → p + n + ν x3 neutrondetectionmethods:n + d → t + γ + 6.25n+ 35 Cl→ 36 Cl + γ + 8.6n+ 3 He → p + t + 0.76ESCCNCMeVMeVMeV3 Phases: • Just D 2 O• D 2 O + 2 tonnes NaCl• D 2 O + 3 He Proportional Counters (“NCDs”)


Solar Neutrino Program1998 1999 2000 2001 2002 2003 2004 2005 2006Comm.D 2OD 2 OReturnSNOSaltD 2ODataAnalysis3HeSuper-KamiokandeCl-ArBorexinoSAGE & GNOKamLANDKamLAND Solar3


391- day salt resultsφφφCCNCES= 1.68= 4.94= 2.35+ 0.06−0.06+ 0.21−0.21+ 0.22−0.22(stat.)(stat.)(stat.)+ 0.08−0.09+ 0.38−0.34+ 0.15−0.15(syst.)(syst.)(syst.)φφCCNC=0.340 ±0.023(stat.)+ 0.029−0.031In units of 10 -6 cm -2 s -1∆m 2 = 8.0 +0.4 −0.3×10 −5 eV 2+1.6θ = 33.9 −1.6degPRC 72, 055502 (2005)4


Why use NCDs?The features:• Different systematics from other Phases.• Separate signal paths: neutron capture no longercompetes with CC events in Cherenkov light.• Break correlation between CC and NC signals.• CC spectrum contamination by 6.25-MeV capturegammas reduced by capture in NCD array, anddetermined independently.The difficulties:• Signal rate low: ~1000 neutrons/year detected.• Ultra-low background materials needed.• Some light loss (~10%) due to array.• Complexity.5


Chemical Vapor Deposition:Ni + 4CO ↔ Ni(CO) 4Strong, ultrapure Ni shapes.1Background alpha rate < best previous.100Endcaps


Phase IIICounters 2 - 3m long laser-weldedtogether and deployed by asubmersible vehicle.36 strings of 3 He, 4 strings of 4 Heon a 1 x 1 m grid.Total length 398 m


8Energy Spectrum from 3 He(n,p)tNeutrons from 24 Na: γ + d→p + nEvents per 10 keV191 keV573 keV764 keVnNi wall3 He:CF4 gasCu anode wirep t573 191573191


NCD Electronics - Data AcquisitionCurrentPreamp(1 of40)Multiplexer (1 of 4)12 Input Channels / MUXDigitalScopeDigitalScopespectrumpulse• Ionization current pulses digitized for detailed analysis.• Currents integrated by analog circuits for precise,nearly deadtimeless, charge measurement.9


Calibrating the Neutron Efficiency• Solar neutrinos produce neutrons uniformly in the D 2 O.• Monte Carlo based on Los Alamos “MCNP” code yields efficiency of0.210(3).• Time-series analysis (which is independent of source strength) ofneutron bursts from 252 Cf fission confirms Monte Carlo precision.• Neutron efficiency canalso be measuredexperimentally: Dissolve24NaCl brine in the D 2 O,mix well.• 15-hr 24 Na: 2.75-MeV γbreaks up deuteron,liberates a neutron.• A uniform source!10


Calibrating the Neutron Efficiency• Mixing 24 NaCl with the D 2 O.See poster by C. KrausNormalized ratio of Cherenkov light at many points in vessel: 2006 data/ 2005 data.Different brine injection methods. Equalized ratio indicates uniform mixing.First day after injection During mixing Steady stateNeutron efficiency: 0.211(7) for NC signal.Excellent agreement with Monte Carlo: 0.210(3)11


Cutting instrumental eventsAmplitudeSum of 10 stringsRejectEnergy spectra of 2 stringsshowed instrumentalevents that could not becompletely cut fromneutron/alpha events.AcceptNeutronpeak pos.NeutronsAlphasCharge6 3 He strings in total were dropped from theanalysis.These strings were droppedand PDFs were added in theanalysis to allow for suchevents to be present 12 onother strings.


Neutron-capture spectrum (blind data)3He(n,p) 3 HCounts per 10 keVAlpha backgroundEnergy (MeV)13


Blind AnalysisThree blindfolds for the analysts:• First month of neutrino data open• Then only 20% open to 12/05 tofinalize instrumental backgroundcuts• Thereafter include hidden fractionof neutrons that follow muons, AND• Omit an unknown fraction ofcandidate eventsDetailed internal documentation,review by “topic committees”Box Opened May 2, 2008• Results presented are as found,except…• Difference between uncertaintiesfrom 3 signal-extraction codes: “Piloterrors” corrected, no change incentral values, uncertainties agree.• An incorrect algorithm in fitting thepeak value of the ES posteriordistributions replaced.


Neutrons from solar neutrino interactionsNC Signal:983 ± 77Neutronbackground:185 ± 25Alphas andInstrumentals:6126 ± 250(0.4 to 1.4 MeV)15


BackgroundsSourcePMT Events(neutrons)NCD Events(neutrons)D 2 O RadioactivityAtmospheric ν, 16 NOther backgroundsNCD Bulk PD, 17,18 O(α,n)NCD hotspotsNCD cablesExternal-source neutronsTOTAL7.6 ± 1.224.7 ± 4.60.7 ± 0.14.6 +2.1 -1.617.7 ± 1.81.1 ± 1.020.6 ± 10.477 +12 -1028.7 ± 4.713.6 ± 2.72.3 ± 0.327.6 +12.9 -10.364.4 ± 6.48.0 ± 5.240.9 ± 20.6185 +25 -2216


NCD SimulationResultsfull model of detector physicsto simulate pulse shapecharacteristics, correlationstuned on calibration dataPulse Width ns)Pulse duration, nsdataPulse Width (ns)Pulse duration, nsMCEnergy (MeV)Energy, MeVneutron signalEnergy, (MeV)alpha backgrounds:surface polonium decaybulk U and Th decaywire polonium decaywire bulk decayinsulator polonium decayinsulator bulk U and Th decay18


Markov Chain Monte Carlo FitThe physics parameters (“fluxes”) are fitted allowing nuisanceparameters (calibration constants, etc.) to vary weighted bytheir external uncertainties. The likelihood is maximized viarandomized search steps. See poster by B. Jamieson.Algorithm:Initial step iparameter guesses p icalculate likelihood L iAdd random amounts to allparameters:p i+1 = p i + Norm(0,σ i )calculate likelihood L i+1Keep p i or p i+1 :p keep =max(1, L i+1 / L i )19


PMT Distributions - cos(θ sun ), EnergyData fromsalt phase20


SNO NC Flux: 3 PhasesNC Flux (corrected to 8 B spectrum of Winter et al.)CC spectrum shape not constrained to 8 B shape.statstat + syst21


SNO CC Flux: 3 Phases22


SNO, S-K ES Fluxp-value for consistency of NC/CC/ESin the salt & NCD phases + D 2 ONC(unconstr) is 32.8%23


Results from SNO NCD Phase & Super-KPreliminaryFluxes(10 4 cm -2 s -1 )ν e : 167(9)ν ES : 177(26)ν total : 554(48)ν SSM : 569(91)φ SSM = 569(1±0.16) x 10 4 cm -2 s -1 (BSB05-OP:Bahcall, Serenelli, Basu Ap. J. 621, L85, 2005).Super-K: PRD 73, 112001, 200624


2-Neutrino Oscillation ContoursSNO onlyPreliminaryCl-ArSuper-KSAGEGallexGNOSNOBorexino766 t-y KamLANDPreliminarySolar Solar +KamLANDPreliminary25


Solar + KamLAND fitresults (preliminary)∆m 2 = 7.94 +0.42 −0.26×10 −5 eV 2tan 2 +0.047θ = 0.447 −0.043+1.4θ = 33.8 −1.3degreesφ 8B= 0.873(1± x)φ 8B(BSB 05−OP )2-neutrino mixing model.Marginalized 1-σ uncertainties.All SNO phases.KamLAND: PRL 94, 081801 (2005).to be published later.xThis work:• NCD results agreewell with previous SNOphases. Minimalcorrelation with CC.Different systematics.• New precision on θFuture work:• 3-phase analysis• 3-neutrino analysis• LETA (Low EnergyThreshold Analysis)• hep flux• Day-night, othervariations• Muons, atmospheric ν


The SNO CollaborationB. Beltran, S. Habib, A.L. Hallin, C. Howard, C.B. KraussUniversity of AlbertaB. Jamieson, S.M. Oser, T. Tsui, J. WendlandUniversity of British ColumbiaR.L. Hahn, R. Lange, M. YehBrookhaven National LaboratoryA.Bellerive, K. Boudjemline, P.-L. Drouin, K. Graham,R.J. Hemingway, C. Mifflin, E. Rollin, O. Simard, L. Sinclair,G. Tesic, D. Waller, F. ZhangCarleton UniversityP. Jagam, J. Law, B.G. Nickel,R.W. Ollerhead, S.D. Reitzner, J.J. SimpsonUniversity of GuelphB. Aharmim, D. Chauhan, J. Farine, F. Fleurot, E.D. Hallman,M. Huang, A. Krueger, M.H. Schwendener, C.J. VirtueLaurentian UniversityM. Bergevin, Y.D. Chan, C.A. Currat, R. Henning, K.T. Lesko,A.W.P. Poon, G. Prior, N. TolichLawrence Berkeley National LaboratoryN. Barros, J. ManeiraLIP, LisbonJ. Banar, T.J. Bowles, S.R. Elliott, M.M. Fowler,A. Goldschmidt, A. Hime, G.G. Miller, K. Rielage,L.C. Stonehill, J.B. Wilhelmy, J.M. WoutersLos Alamos National LaboratoryT. JM. Goon, T. Kutter, K. McBrydeLouisiana State UniversityJ.A. Formaggio, M.L. Miller, B. Monreal, J. Monroe,R.A. Ott, T.J. WalkerMITS.D. Biller, B.T. Cleveland, G. Doucas,H. Fergani, N.A. Jelley, J.C. Loach, S. Majerus,H.M. O’Keeffe, G.D. Orebi Gann, P.M. Thornewell,H. Wan Chan Tseung, N. West, J.R. Wilson, K. ZuberOxford UniversityE.W. Beier, H. Deng, M. Dunford, W.J. Heintzelman,C.C.M. Kyba, N. McCauley, J.A. Secrest, R. Van BergUniversity of PennsylvaniaS.N. Ahmed, B. Cai, M. Chen, X. Dai, M. DiMarco, E.D. Earle,H.C. Evans, G.T. Ewan, E. Guillian, P.J. Harvey, J. Heise,K.J. Keeter, L.L. Kormos, M.S. Kos, C. Kraus, J.R. Leslie,R. MacLellan, H.B. Mak, R. Martin, A.B. McDonald, A.J. Noble,B.C. Robertson, P. Skensved, A. Wright, Y.TakeuchiQueen’s UniversityF. Duncan, R. Ford, I.T. Lawson, B. MorissetteSNOLABR.L. HelmerTRIUMFA.E. Anthony, J.R. Klein, S. Seibert, C.D. TunnellUniversity of Texas at AustinJ.F. Amsbaugh, M.C. Browne, T.V. Bullard, T.H. Burritt,G.A. Cox-Mobrand, J. Detwiler, P.J. Doe, C.A. Duba, N. Gagnon,J.V. Germani, A. Hamian, G.C. Harper, R. Hazama, K.M. Heeger,M.A. Howe, S. McGee, A. Myers, N.S. Oblath, R.G.H. Robertson,M.W.E. Smith, T.D. Steiger, B.A. VanDevender,T. Van Wechel, B.L. Wall, J.F. WilkersonUniversity of Washington


SNO Collaboration28


New Measurements of 8 B ν SpectrumWinter, Freedman, et al.PRL 91 252501, NP A746,311 (2004).Bhattacharya et al. PRC73:055802,2006Ortiz et al.30


Change in parameterization for ES fitOld methodNew method31


Angular distributions for ES in 3 Energy bins6.0 - 6.5 MeV 6.5 - 7.0 MeV 7.0 - 7.5 MeV32


Energy spectra, salt phaseElectron kinetic energy34


Energy spectraElectron kinetic energy35


Cutting instrumental eventsRejectAcceptNeutronsAlphas36


SNO gratefully acknowledges…Canada:US:Natural Sciences and Engineering Research CouncilIndustry CanadaNational Research CouncilNorthern Ontario Heritage FundVale IncoAtomic Energy of Canada, Ltd.Ontario Power GenerationHigh Performance Computing Virtual LaboratoryCanada Foundation for InnovationCanada Research ChairsWestgridDepartment of EnergyNERSC PDSFUK:STFC (formerly Particle Physics and Astronomy Research Council)Portugal:FCT37

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