Results and Prospects for SNO Low Energy Threshold Analysis (LETA) Motivations Analysis Details Results Status of `three-phase’ Analysis Summary and Other Recent Results Josh Klein, for the SNO Collaboration University of Pennsylvania 15 June 2010

Sudbury Neutrino Observatory neutrino reactions on deuterons National Geographic Neutrino-Electron Scattering (ES) Charged Current (CC) Neutral Current (NC) Signal rates determined by statistical fit

Three Phases of SNO Phase I: Just D2O Simple detector configuration, clean measurement Low neutron sensitivity Poor discrimination between neutrons and electrons Phase II: D2O + NaCl Very good neutron sensitivity Better neutron electron separation Phase III: D2O + 3He Proportional Counters Good neutron sensitivity Great neutron/electron separation

Low Energy Threshold Analysis Motivations: ne Statistics CC En=6 MeV ES En=6 MeV Night Day

Low Energy Threshold Analysis Motivations: NC Precision nx (NC) Statistics Breaking NC/CC Covariance Phase I (D2O) NC +74% +68% Phase II (D2O+NaCl) I “Beam Off” Low n capture eff. II “Beam On” High n capture eff.

Low Energy Threshold Analysis Overview Key components: Joint-Phase (I+II) fit for all signals and remaining bkds Reduction of Backgrounds Reduction of Systematic Uncertainties `Float’ Dominant Uncertainties in Fit Needed to rework SNO’s entire analysis chain and simulation, from measurement of charge pedestals to final fit methods. Results: 8B flux measured by NC rates Bin-by-bin electron energy spectrum using CC & ES Parameterized Psurv(En) (New) Two-flavor and three-flavor extraction of mixing params.

Low Energy Threshold Analysis Signal Extraction Fit (Signal PDFs) Monte Carlo Not used (unconstrained in fit) Teff (MeV) cosqsun (R/RAV)3 Isotropy = 1-D projections of 3-D and 4-D PDFS

Low Energy Threshold Analysis Low Energy Backgrounds Cosmic rays < 3/hour Teff>3.5 MeV All events ( but only ~5000 ns) D2O Acrylic Vessel H2O }×{ + PMT 208Tl Acrylic Vessel Surface Neutrons [(α,n) reactions] 214Bi (U, Rn) 208Tl (Th) 24Na (neutron activation of salt) = 12 external bkds + 5 internal bkds (most backgrounds constrained by ex-situ radioassays) For each phase

Low Energy Threshold Analysis Low Energy Backgrounds Kinetic Energy Spectrum New Threshold = 3.5 MeV MC PMT b-gs internal (D2O) external (AV + H2O) NC+CC+ES (Phase II) Old threshold 3 neutrino signals + 17 backgrounds ALL MC!!

Low Energy Threshold Analysis Signal Extraction Fit (3 out of 17(x2) Background PDFs) Monte Carlo Teff (MeV) cosqsun (R/RAV)3 Isotropy = 1-D projections of 3-D and 4-D PDFS

Low Energy Threshold Analysis Background Reduction: Energy Resolution Time Residual (ns) Prompt Timing Cut Late Timing Cut Rayleigh Scatter (used in prior analyses) Using all hits increased hit statistics by ~12% ->6% reduction in resolution ~60% reduction internal bkds `Prompt’ (direct) light easy to model: we know the path traveled

Low Energy Threshold Analysis Background Reduction: New Cuts Only information is PMT charges, times, and hit patterns 4 KS tests of PMT pattern against single Cherenkov e- 1 KS test of PMT times against Cherenkov e- 3 cuts on various isotropy parameters 2 cuts on energy reconstruction uncertainty In-time ratio vs. Nhit to remove misreconstructed events

Low Energy Threshold Analysis Background Reduction: New Cuts `Early’ Charge to cut PMT b-gs Fiducial Volume β γ High charge early in time Note: This would have been impossible if we hadn’t fixed `little’ things like charge pedestals

Low Energy Threshold Analysis Special Case: PMT b-g PDFs Not enough CPUs to simulate sample of events Use data instead PassFail FailPass FailFail PassPass Early charge probability Early charge probability In-time ratio In-time ratio `Bifurcated’ analysis 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 Analysis Systematic Uncertainties: Brief Summary 0% 1% 3% 4% 2% n capture Teff scale Fiducial volume I II LETA I LETA II N/A I=D2O II=D2O+Salt b14 (isotropy)

Low Energy Threshold Analysis Systematic Uncertainties And shows clear ES peak, even at 3.5MeV threshold

Low Energy Threshold Analysis Tests of PDF shapes Comparison of 208Tl calibration source data to MC Run near the AV (to model AV 208Tl events) And shows clear ES peak, even at 3.5MeV threshold

Low Energy Threshold Analysis Tests of PDF shapes Distributed Rn Spike And shows clear ES peak, even at 3.5MeV threshold Fit to spike energy spectrum allowing Teff scale to float: shift is 0±0.6%

Low Energy Threshold Analysis Signal Extraction Fit (3 signals+17 backgrounds)x2, and pdfs are multidimensional: ES, CC NC, backgrounds Two distinct methods: 1. Maximum likelihood with binned pdfs:  Manual scan of likelihood space Data helps constrain systematics `human intensive’ 2. Kernel estimation---ML with unbinned pdfs: Further improve syst meast by using data to constrain values of syst pars Allows full `floating’ of systematics, incl. resolutions CPU intensive---use graphics card!

Low Energy Threshold Analysis Fit Results: Binned fit, 1D Projections And shows clear ES peak, even at 3.5MeV threshold

Low Energy Threshold Analysis 8B Flux Results with `unconstrained’ CC spectrum And shows clear ES peak, even at 3.5MeV threshold LETA A LETA B

Low Energy Threshold Analysis `Unconstrained’ CC Electron Spectrum And shows clear ES peak, even at 3.5MeV threshold

Low Energy Threshold Analysis `Unconstrained’ CC Electron Spectrum Flat:2 = 21.52/15 d.o.f. And shows clear ES peak, even at 3.5MeV threshold

Low Energy Threshold Analysis Direct fit to data for Psurv(En) Parameterize distortion to ne spectrum with quadratic Psurv is independent of any flux model: CC and ES rates constrained to be less than NC This helps separate signals and backgrounds: PDFs are now 4D PeeDAY(E) = c0 + c1 (E - 10 MeV) + c2 (E - 10 MeV)2 PeeASYM(E) = a0 + a1 (E - 10 MeV) PeeNIGHT(E) = PeeDAY(E) x [1 + (1/2)*PeeASYM(E)] [1 – (1/2)*PeeASYM(E)] And shows clear ES peak, even at 3.5MeV threshold Note: Fit is now in En, not Teff

Direct Fit for Energy-Dependent Survival Probability Previous global best-fit LMA point: tan212 = 0.468, m2 = 7.59x10-5 eV2 8B = 5.046 +3.8 -3.9 % No distortion, no D/N: 2 = 1.94 / 4 d.o.f. LMA-prediction: 2 = 3.90 / 4 d.o.f. DAY NIGHT ASYM

Comparisons of 8B Spectra J.L. Raaf, Boston University SNO Day Night Borexino arXiv:0808.2868v2

Oscillation Analyses: SNO Only LETA paper 2009: LETA joint-phase fit + Phase III (3He) Best-fit point: tan212=0.437±0.058 m2=1.15x10-7 +0.438-0.18 eV2 (LOW) SNO Collaboration, Phys. Rev C81, 55504

Solar + KamLAND 2-flavor Overlay Brief History KamLAND Collab, Phys.Rev.Lett.90:021802,2003.

Solar + KamLAND 2-flavor Overlay Brief History KamLAND collaboration

Solar + KamLAND 2-flavor Overlay Brief History S. Abe et al. (KamLAND Collaboration), PRL 100, 221803 (2008)

Solar + KamLAND 2-flavor Overlay Brief History LETA paper 2009: LETA joint-phase fit + Phase III + all solar expts + KamLAND

Solar + KamLAND 2-flavor Overlay LETA paper 2009: LETA joint-phase fit + Phase III + all solar expts + KamLAND 2-flavor overlay 2 model

Oscillation Analyses: Solar + KamLAND LETA paper 2009: LETA joint-phase fit + Phase III + all solar expts + KamLAND Best-fit LMA point: tan212 = 0.457 +0.040-0.029 (q12=34.06+1.16-0.84 deg) sin2q12-1/3=-0.02+0.016-0.018 m2 = 7.59x10-5 eV2 (+0.20 -0.21) 2 model 8B uncert = +2.38 -2.95 %

Solar + KamLAND 3-flavor Overlay LETA paper 2009: LETA joint-phase fit + Phase III + all solar expts + KamLAND 3-flavor fit/overlay ->Pointed out by many authors Best-fit: sin213=2.00 +2.09-1.63 x10-2 sin213 < 0.057 (95% C.L.) 3 model

``Three-Phase’’ Analysis Combine LETA+Phase III (3He) in single fit Pulse Shape Analysis to separate 3He signal from background Constrain 3-phase fit using 3He neutron count Output is 8B flux using NC + Psurv(En) +

``Three-Phase’’ Analysis Pulse Shape Analysis Two 2-D Cuts: Hypothesis Test 1 Hypothesis Test 2 Fit to counter pulse energy spectrum used to constrain number of neutrons in full fit See poster by R. Martin, N. Oblath, N. Tolich

``Three-Phase’’ Analysis Pulse Shape Analysis All phases combined with Psurv(En) fit Expected Dm2 improvement Also: expect to bring limits on hep down by x2 See poster by P-L. Drouin, C. Howard, N. Barros

Other SNO Results Low-multiplicity burst search High frequency periodicity search Expected Sensitivity Neutrons and spallation products See poster by A. Anthony, ApJ. 710:540-548 See poster by J. Loach

Summary LETA analysis improved precision on NC by more than factor of 2. Lowest analysis threshold yet achieved by water Cherenkov technique Low E spectrum (still) consistent with no distortion First model-independent fit for solar ne survival probability 3-flavor analysis shows non-zero q13 but consistent with q13=0: Expect further improvement with 3-phase analysis Just a few other things left to do… sin213=2.00 +2.09-1.63 x10-2 sin213 < 0.057 (95% C.L.)

Systematic Uncertainties Position Old New Central runs remove source positioning offsets, MC upgrades reduce shifts Fiducial volume uncertainties (> factor of 3 improvement: Old: Phase I ~ ±3% Phase II ~ ±3% New: Phase I ~ ±1% Phase II ~ ±0.6% Tested with: neutron captures, 8Li, outside-signal-box ns

Systematic Uncertainties Isotropy (b14) MC simulation upgrades provide biggest source of improvement Tests with muon `followers’, Am-Be source, Rn spike b14 Scale uncertainties (factor of 2 improvement): 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

8B Flux Result NC = 5.140 +4.0 -3.8 % And shows clear ES peak, even at 3.5MeV threshold J. N. Bahcall, A. M. Serenelli, and S. Basu, AstroPhys. J. 621, L85 (2005)

Monte Carlo Upgrades Calibrations Parameters for simulation measured and tested with sources Laser source (optics/timing) 16N  6.13 MeV ’s Radon `spikes’ Neutrons 6.25 MeV ’s pT  19.8 MeV ’s 8Li  ’s, E<14 MeV Encapsulated U and Th sources

Systematic Uncertainties Energy Scale No correction With correction 16N calibration source 6.13 MeV gs 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) Tested with: Independent 16N data, n capture events, Rn `spike’ events…

New Cuts Summary ~80% reduction in external bkds

Direct Fit for Energy-Dependent Survival Probability Previous global best-fit LMA point: tan212 = 0.468, m2 = 7.59x10-5 eV2 NIGHT DAY And shows clear ES peak, even at 3.5MeV threshold

Survival Probability DAY NIGHT And shows clear ES peak, even at 3.5MeV threshold NIGHT

Survival Probability DAY NIGHT And shows clear ES peak, even at 3.5MeV threshold NIGHT

Survival Probability DAY NIGHT And shows clear ES peak, even at 3.5MeV threshold NIGHT

Survival Probability DAY NIGHT And shows clear ES peak, even at 3.5MeV threshold NIGHT

Oscillation Analyses: Global Solar LETA paper 2009: LETA joint-phase fit + Phase III + all solar expts Best-fit LMA point: tan212 = 0.457 (+0.038 -0.041) m2 = 5.89x10-5 eV2 (+2.13 -2.16) And shows clear ES peak, even at 3.5MeV threshold