Sudbury Neutrino Observatory Results from the Sudbury Neutrino Observatory Dave Wark Nikhef January 11th, 2002

Fusion in the Sun pp 2H + e+ +e 2H + p 3He + 3He + 3He  4He + 2p pep  2H + e pp 2H + e+ +e 2H + p 3He + 3He + 3He  4He + 2p 3He + 4He 7Be + e + 7Be  7Li +e 7Li + p  2 4He p + 7Be  8B + 8B  8Be* + e+ +e 8Be* 2 4He Dave Wark - Nikhef

Solar Neutrino Fluxes Next three plots adapted from http://www.sns.ias.edu/~jnb/ Dave Wark - Nikhef

The Solar Neutrino Problem Dave Wark - Nikhef

Helioseismology Dave Wark - Nikhef

Helioseismology Dave Wark - Nikhef

The Solar Neutrino Problem Dave Wark - Nikhef

Neutrino Oscillations Let us assume that neutrinos have (different) masses - Dm2 Let us assume that the mass eigenstates are not identical to the weak eigenstates If we consider 2 flavours the mixing is characterized by a single angle q analogous to the Cabibbo angle in case of quarks Dave Wark - Nikhef

Neutrino Oscillations Or : Recall that Consider  = 45 nm ne nm Dave Wark - Nikhef

Vacuum Oscillations In general this leads to the disappearance of the original neutrino flavour With the corresponding appearance of the “wrong” neutrino flavour Dave Wark - Nikhef

The MSW effect ne have an extra diagram for scattering from electrons (W as well as Z exchange) gives ne an “effective mass” in matter proportional to the electron density Ne can lead to an energy dependent resonant enhancement of oscillations for both large (LMA) and small (SMA) mixing angles ( m2/NeE ) The MSW effect Dave Wark - Nikhef

Global fit, 8B Flux a free parameter Includes: Rates: Homestake SAGE GALLEX/GNO Super-K Super-K spectra day night From Bahcall, Krastev, and Smirnov; hep-ph/0103179 Dave Wark - Nikhef

Sterile n solutions Includes: Rates: Homestake SAGE GALLEX/GNO Super-K Super-K spectra day night From Bahcall, Krastev, and Smirnov; hep-ph/0103179 Dave Wark - Nikhef

SNO Dave Wark - Nikhef

The SNO Detector Surface: 2 km Phototube Support 1000 tonnes D2O Structure (PSUP) 1000 tonnes D2O Acrylic Vessel 104 8” PMTs 6500 tonnes H2O Dave Wark - Nikhef

n Reactions in SNO e p d + Þ n Þ ne only CC - e p d + Þ n Good measurement of ne energy spectrum Weak directional sensitivity  1-1/3cos(q) Dave Wark - Nikhef

Čerenkov Light Production Charged current interaction in D2O Dave Wark - Nikhef

n Reactions in SNO e p d + Þ n Þ n + Þ p d Þ + Þ e ν Þ ne only CC - e p d + Þ n Good measurement of ne energy spectrum Weak directional sensitivity  1-1/3cos(q) NC x n + Þ p d Þ Equal cross section for all n types Measure total 8B n flux from the sun. ES - + Þ e ν x Þ All n types but enhanced sensitivity to ne Low Statistics Strong directional sensitivity Dave Wark - Nikhef

The enemy….. bs and gs from decays in these chains interfere with our signals at low energies And worse, gs over 2.2 MeV cause d + g  n + p Design called for: D2O < 10-15 gm/gm U/Th H2O < 10-14 gm/gm U/Th Acrylic < 10-12 gm/gm U/Th Dave Wark - Nikhef

Construction Dave Wark - Nikhef

Water Systems Dave Wark - Nikhef

SNO Water Assays Targets for D2O represent a 5% background from d+g  n+p Targets are set to reduce b-g events reconstructing inside 6m Dave Wark - Nikhef

Signals in SNO NC Salt (BP98) Dave Wark - Nikhef

Smoking Guns in SNO - 1 CC/ES Could also show significant effects! Charged-Current to Neutral Current ratio is a direct signature for oscillations CC/ES Could also show significant effects! 0.15 Dave Wark - Nikhef

Charged-current spectrum is more sensitive to shape Smoking Guns in SNO - 2 ES CC Charged-current spectrum is more sensitive to shape distortions. Day/Night effects possible Dave Wark - Nikhef

A Neutrino Event Dave Wark - Nikhef

Signals in SNO NC Salt (BP98) Dave Wark - Nikhef

Instrumental Backgrounds Note Neck Tubes Fired Electronic Pickup Dave Wark - Nikhef

Instrumental Background Cuts Dave Wark - Nikhef

How do we know this worked ? We did it twice. Two different semi-independent sets of cuts were developed. Dave Wark - Nikhef

How do we know this worked? Number of phototubes hit Fraction of good events cut Fraction of hits in a prompt time window Mean angle between phototube hits Contamination measured with independent cuts Signal loss measured with calibration sources Dave Wark - Nikhef

Solar Neutrino Spectrum Dave Wark - Nikhef

Current SNO data set Data Period: 2/11/99  15/01/01 Livetime: 240.9 Days Data set 1: Analysis Data used to develop the data analysis ~166 days livetime Data set 2: Blind data test for statistical bias ~75 days livetime No statistically significant differences seen results from full data set shown here Dave Wark - Nikhef

SNO Livetime Dave Wark - Nikhef

Manipulator Dave Wark - Nikhef

SNO Energy Calibrations 252Cf neutrons b’s from 8Li g’s from 16N and t(p,g)4He Dave Wark - Nikhef

Backgrounds from the Data External g-ray background bg background from the AV bg background from the H2O bg background from the PMTs Dave Wark - Nikhef

Acrylic Vessel Assay (~1/10) the target level of 2 ppt U/Th Every piece sampled and tested Sample bonds tested Direct Assay by Čerenkov light AV well below (~1/10) the target level of 2 ppt U/Th “Berkeley Blob” 9 +20  3 mg “Th” -5 Dave Wark - Nikhef

Signal Extraction Threshold set at Teff = 6.75 MeV removes most of the neutrons further reduces the background Fit resulting events to Probability Density Functions (pdfs) in: effective energy: Teff volume weighted position: (R/RAV)3 angle from the Sun: cosq Dave Wark - Nikhef

Signal Extraction Teff (R/RAV)3 cosq Dave Wark - Nikhef

Signal Extraction Threshold set at Teff = 6.75 MeV removes most of the neutrons further reduces the background Fit resulting events to Probability Density Functions (pdfs) in: effective energy: Teff volume weighted position: (R/RAV)3 angle from the Sun: cosq Use maximum likelihood to extract components CC = 975.4 ± 39.7 events ES = 106.1 ± 15.2 events neutrons = 87.5 ± 24.7 events Dave Wark - Nikhef

SNO cosq distribution Electron Angle with respect to the direction from the Sun ES: strongly peaked CC: 1-1/3cosq Neutrons: isotropic Dave Wark - Nikhef

SNO energy spectrum from unconstrained fit Data points derived by fitting each energy bin independently Monte Carlo of undistorted 8B spectrum normalized to the data Dave Wark - Nikhef

SNO energy spectrum from an unconstrained fit Ratio to BP2001: 0.347 ± 0.029 (Adding syst. bin by bin in quadrature give c2 of ~12 for 11 D.O.F.) Dave Wark - Nikhef

SNO energy spectrum from an unconstrained fit Ratio to BP2001: 0.347 ± 0.029 (Adding syst. bin by bin in quadrature give c2 of ~12 for 11 D.O.F.) Dave Wark - Nikhef

SNO energy spectrum from an unconstrained fit New Super K Flux Ratio to BP2001: 0.347 ± 0.029 (Adding syst. bin by bin in quadrature give c2 of ~12 for 11 D.O.F.) Dave Wark - Nikhef

Solar Neutrino Fluxes NB: All fluxes quoted are in units 106/cm2/sec Absolute fluxes from constrained fit: CC (8B) = 1.75 ± 0.07 ± 0.05 (stat) (sys.) (theory) ES (8B) = 2.39 ± 0.34 (stat) (sys.) +0.12- 0.11 +0.16 - 0.14 SNO: NB: All fluxes quoted are in units 106/cm2/sec Dave Wark - Nikhef

Systematic Flux Uncertainties Error Source Energy scale Energy resolution Non-linearity Vertex shift Vertex resolution Angular resolution High Energy ’s Low energy background Instrumental background Trigger efficiency Live time Cut acceptance Earth orbit eccentricity 17O, 18O Experimental uncertainty Cross-section Solar Model CC error (%) -5.2, +6.1 ±0.5 ±3.1 ±0.7 -0.8, +0.0 -0.2, +0.0 0.0 ±0.1 -0.6, +0.7 ±0.2 -6.2, +7.0 3.0 -16, +20 ES error (%) -3.5, +5.4 ±0.3 ±0.4 ±3.3 ±2.2 -1.9, +0.0 -0.2, +0.0 -0.6, +0.0 0.0 ±0.1 -0.6, +0.7 ±0.2 -5.7, +6.8 0.5 -16, +20 Dave Wark - Nikhef

Solar Neutrino “Fluxes” Absolute fluxes from constrained fit: CC (8B) = 1.75 ± 0.07 ± 0.05 (stat) (sys.) (theory) ES (8B) = 2.39 ± 0.34 (stat) (sys.) +0.12- 0.11 +0.16 - 0.14 SNO: +0.08 - 0.07 ES (8B) = 2.32 ± 0.03 (stat) (sys.) Super-K* *S. Fukuda, et al., hep-ex/0103032 Dave Wark - Nikhef

“Flux” Differences The hypothesis that this is a downward CC at SNO vs ES at SNO ES - CC = 0.64 ± 0.40  1.6 effect SNO CC at SNO vs ES at SK ES - CC = 0.57 ± 0.17  3.35 effect SK SNO The hypothesis that this is a downward statistical fluctuation is ruled out at 99.96% Dave Wark - Nikhef

John Bahcall has been right all these years! Ftotal vs. Fe You can extract the total neutrino flux from these results: SNO (8B) = 5.44 ±0.99  106 cm-2s-1 -SK This can be compared to the SSM prediction: +1.01 - 0.81 SSM (8B) = 5.01  106 cm-2s-1 John Bahcall has been right all these years! Dave Wark - Nikhef

Using the 8B flux to constrain G and WIMPS See Lopes and Silk, astro-ph/0112310 See Lopes and Silk, astro-ph/0112390 Dave Wark - Nikhef

Allowed Solutions for Neutrino Oscillations Flavour Oscillations Sterile Oscillations Dave Wark - Nikhef

Equalizing SNO/SK n response CC and ES have different En response However, choosing different thresholds can compensate For the current analysis, Tthresh = 6.75 MeV for SNO and 8.6 MeV for Super-K equalize response to few % From G.L. Fogli et al., hep-ph/0106247 For these thresholds the “fluxes”still differ by 0.53 ± 0.17 Sterile oscillations ruled out by this test at > 3s Dave Wark - Nikhef

Allowed Solutions for Neutrino Oscillations Flavour Oscillations Sterile Oscillations Dave Wark - Nikhef

Oscillation Analyses including SNO Barger, Marfatia and Whisnant: hep-ph/0106207 Oscillations to partially sterile neutrinos still allowed Fogli et al.: hep-ph/0106247 Purely sterile oscillations ruled out at >3s SMA flavoured oscillations also ruled out Dave Wark - Nikhef

Allowed regions from Fogli et al. Before SNO After SNO Dave Wark - Nikhef

Oscillation Analyses including SNO Barger, Marfatia and Whisnant: hep-ph/0106207 Oscillations to partially sterile neutrinos still allowed Fogli et al.: hep-ph/0106247 Purely sterile oscillations ruled out at >3s SMA flavoured oscillations also ruled out Bahcall, Gonzalez-Garcia, Pena-Garay: hep-ph/0106258 No, at 3s everything still allowed Bandyopadhyay et al.: hep-ph/0106264 Includes SNO energy spectrum SMA ruled out Berezinsky: hep-ph/0108166 SNO was right about everything…. Krastev and Smirnov: hep-ph/0108177 No they weren’t, but neither are the others….. Dave Wark - Nikhef

What is going on? Why do these analyses differ? Which one is right? Different handling of spectral oversampling Slightly differences in the methods Which one is right? Beats me….. As Rutherford said, if you need a statistical test, you did the wrong experiment. Dave Wark - Nikhef

The Right Experiment SNO Neutral Current Measurement Pure D2O - data in can, results soon Salt data now being taken Higher efficiency for neutron capture Capture signal at higher E, clear of background Independent test for NC/CC discrimination Different systematics Discrete NCDs to be deployed next Stringent test for non-electron neutrino appearance Dave Wark - Nikhef

Conclusions The SNO detector is working and taking beautiful data. The CC rate measured in SNO is incompatible with the Super-K ES rate. This is strong evidence (>99.8% c.l.) for the appearance of m or t neutrinos from the Sun. Sterile and Just-So2 oscillations are excluded by these results at >99.8% c.l. The 8B n flux from the Sun is now measured to be in agreement with the predictions of the Standard Solar Model. +Super-K+T2 b decay  0.001 < Wn < 0.18 Dave Wark - Nikhef

Outlook NC measurements in pure D2O These results are just the first of what SNO will produce. The conclusions listed on the preceeding slide are systematics dominated. They will be severely tested by new measurements: NC measurements in pure D2O Day/night in pure D2O The same measurements with NaCl added The same measurements with the NCDs Borexino and KamLAND will give additional information in the near future The future - SIREN, LENS, etc. Dave Wark - Nikhef

Outlook Solar Neutrinos have demonstrated (confirmed?) that neutrinos have mass and undergo flavour oscillations Now we must understand why….. Dave Wark - Nikhef