First Results from Phase II of the Sudbury Neutrino Observatory Joshua R. Klein University of Texas at Austin  Solar Neutrinos  Review of Phase I Solar Results  Phase II Analysis and First Results  Phase III Plans

The Beam Spectra determined by nuclear physics, not solar model Starts out as pure e …

Solar Neutrino Experiments First experiment by Davis et al in 1960’s Radiochemical Method (Chlorine): Found ~ 1/3 of expected rate

After Six Solar Experiments 3 Gallium (Radiochemical) 1 Chlorine (Radiochemical) Kamiokande + Super-Kamiokande (Water Cerenkov)

Introduction to Oscillations “Most natural explanation for measurements” Neutrinos are produced weak interaction (flavor) eigenstates ( e, , ,…) but propagate in mass eigenstates ( 1, 2, 3,…) The e survival probability for two flavor mixing is:

Introduction to Oscillations Neutrinos are produced weak interaction (flavor) eigenstates ( e, ,…) but propagate in mass eigenstates ( 1, 2,…) c ij = cos  ij, s ij = sin  ij, CP phase  For three neutrino flavors, mixing is described by 3x3 matrix, analogous to quark sector

Matter (MSW) Effects Signatures: spectral distortion, time variation, depending on mixing angle:    e 

Sudbury Neutrino Observatory Main goal: Direct observation of solar neutrino flavor change via inclusive appearance

The Sudbury Neutrino Observatory A collaboration of Chemists, Nuclear Physicists, and Particle Physicists Canada Carleton U. U. British Columbia U. of Guelph Laurentian U. Queens U. U.K. U. of Oxford United States Brookhaven Lab Los Alamos Lab LBL U. of Pennsylvania U. of Washington U. of

Sudbury Neutrino Observatory 1700 tonnes Inner Shielding H 2 O 1000 tonnes D 2 O 5300 tonnes Outer Shield H 2 O 12 m Diameter Acrylic Vessel Support Structure for 9500 PMTs, 60% coverage Urylon Liner and Radon Seal

Calibration System and Sources Diffusing laser source (optics/timing) 16 N  6.13 MeV  ’s p,T  19.8 MeV  ’s Neutrons  6.25 MeV  ’s 8 Li   ’s, E<14 MeV Encapsulated U and Th sources Manipulator system allows flexible source placement Wide variety of sources for systematic studies

Reactions in SNO Good measurement of e energy spectrum Weak directional sensitivity  1-1/3cos(  ) Measure total 8 B flux from the sun. Equal cross section for all types NC xx  npd ES --  eνeν xx Mainly sensitive to e,, some sensitivity to  and  Strong directional sensitivity CC - eppd  e

Inclusive  Appearance Advantages: NC gives total flux directly Cross section uncertainties cancel Advantages: ES excess points to Sun Can match energy regimes Super-K precision measurement Two possibilities:

Radioactive Backgrounds Cosmic rays < 3/hour

Number of Hit PMTs  Energy Counts Reconstructed inside D 2 O per year Addition of NaCl increases capture probability and energy of emitted  -ray Signal/Background Spectra  Monte Carlo predictions for pure solar e Prospects for measurement in pure D 2 O phase not optimistic

Extracting Signals Can use derived observables (R 3, cos  sun, and E) to produce pdfs. Max. Likelihood fit for relative signal amplitudes Energy Distribution Radial Distribution (R 3, R AV =1) Solar Direction Distribution

Extraction Prerequisites Data Processing Remove backgrounds Reconstruct position and energy Signal Extraction Final fits to data Calculation of fluxes Background Measurement Determine remaining contamination Model Building For producing distributions Calculating acceptances

Phase I (Pure D 2 O) Results SNO measurements: (units 10 6 cm -2 s -1 )  Flux Measurements (Standard 8 B shape assumed) Can resolve these directly into neutrino flavors

Phase I (Pure D 2 O) Results  The non- e solar flux (units 10 6 cm -2 s -1 ) A change of variables gives: `Null hypothesis’ of   =0 rejected at ~ 5  level.

Phase I (Pure D 2 O) Results  SNO Compared to Other Solar Expts.

Looking for the Matter Effect A CC = A NC Unconstrained: AE=AE= A NC =0:

Phase I (Pure D 2 O) Results  Constraints on Mixing Parameters

Including KamLAND Reactor Experiment

The Story So Far SNO Phase I results reject null hypothesis  Independent of solar flux model  Large Mixing Angle region strongly favored…  …but precision limited by SNO CC/NC anticorrelations…  …and total 8 B flux measurement oscillation-dependent. Striking confirmation from KamLAND  Only Large Mixing Angle region left (assuming CPT…)  Maximal mixing still good possibility Specific signatures of matter (MSW) effect as yet unobserved (mixing parameters are `unlucky’).

SNO Phase II (Salt Phase)  Advantages of NaCl: Capture Efficiency 35 Cl has ~4x higher n capture rate than d Total E emitted ~ 2 MeV higher 2 tons of NaCl added June 1, 2001 n 36 Cl * 35 Cl 36 Cl 

SNO Salt Phase  Advantages of NaCl: Event Isotropy How to characterize? Mean Pair Angle (  ij ) Legendre Terms (  14 ) Two-pt Correlation Fcn Tests  multiplicity means PMT hit pattern for neutron events more isotropic than for single Cerenkov electrons simplest Better separation+ Ease of systematic characterization Best separation

SNO Salt Phase  Did this work? Salt E spectrum compared to D 2 O Phase Salt Isotropy Distsribution Compared to D 2 O phase

SNO Phase II (Salt Phase)  Blind Analysis Goal is to ensure independence from pure D 2 O phase Two Approaches: A.NC: Accept small (unknown) number of muon follower neutrons, use `spoiled’ NC cross section in flux calcs B. CC/ES: pre-scale data set by 80+/-10%

SNO Phase II (Salt Phase)  Advantages of NaCl: Signal Extraction Energy Distribution Radial Distribution (R 3, R AV =1) Solar Direction Distribution Isotropy Distribution CC ESNC All New NC Shifted NC Changed Unchanged Covariances between Isotropy and Energy actually require 2D PDFs

Extraction Prerequisites Data Processing Remove backgrounds Reconstruct position and energy Signal Extraction Final fits to data Calculation of fluxes Background Measurement Determine remaining contamination Model Building For producing distributions Calculating acceptances

 Data from August, October, 2003  Trigger threshold at 16 PMTs (roughly 2 MeV)  Run selection criteria: Number of channels online No calibration sources (or calibration activation*) Run terminated normally Trigger rates lower than x3 above nominal =20 Hz  Total of 254 live-days over this period Data Processing  Data Set

Data Processing  Instrumental Background Removal Types: Flasher PMTs Static discharge Electrical noise Isotropic Acrylic Vessel events Low Level Criteria: Charge and mean charge Raw time distributions Event time correlations Veto PMT tags

Instrumental Cuts Spallation and `Follower Neutron’ Cuts (< 20 s after muon) Atmospheric neutron cuts ( 100 events) `Cerenkov Box’ Cuts on narrow timing and Cerenkov angle Fiducial volume (R fit < 550 cm) Energy Threshold (T eff > 5.5 MeV) Data Processing  Summary of All Cuts 435,721,068 triggers 3055 candidates

Salt Phase: Model Building Test with radioactive sources : 16 N  6.13 MeV  ’s Neutrons  6.25 MeV  ’s 8 Li   ’s, E<14 MeV Low energy radioactive sources Energy Position and direction neutron capture Particle ID (e vs. n) Need to know how detector measures: Input to model: Physics measured optics and PMT resp. measured electronics response detector state

Salt Phase: Model Building  Changing Energy Response Energy scale drift HV drift Gain drift Threshold drift Attenuation changes Concentrator degradation  Looked at: Energy Response vs. Date.

 Comparison of Modeled E response to Data Salt Phase: Model Building Calibration Source Data vs. Monte Carlo Uncertainty on energy scale = 1.1%

 Comparison of Modeled Isotropy to Data Salt Phase: Model Building Uncertainty on isotropy mean 0.86%

Salt Phase: Model Building  Measured neutron capture vs radial position Total detection efficiency in salt phase.

Background Measurement  Sources of Background Instrumental  After all cuts, some leakage possible Cerenkov events (  -  ’s)  Energies fluctuate above analysis threshold  Or (mis)reconstruct within fiducial volume  Or actually have high energies (eg comic ray spallation nuclei) Neutrons Created by  Photodisintegration of deuterons by  ’s  Cosmic ray muons  Atmospheric neutrinos  ( ,n) processes  Natural fission  Antineutrinos

Legendre Coefficients (  14 ) Fraction of hits in prompt time window Background Measurement Eliminate residual instrumentals by requiring events to have Cerenkov characteristics: Narrow timing Cerenkov hit pattern  Instrumental Background `Contamination’ Instrumental Background Even with looser isotropy cut for salt phase, residual contamination lower than few events. Remaining isotropic `AV’ events Measured with D 2 O and MC methods

Background Measurement  Cerenkov Events Inside Signal Box Primarily U and Th chains+ 24 Na in Salt Phase Sources of U and Th chain decays: Residual H 2 O/D 2 O contamination PMT support and array Radon from mine air Acrylic vessel contaminants

Background Measurement Ex-situ (radioassays)  Ion exchange ( 224 Ra, 226 Ra)  Membrane Degassing ( 222 Rn)  Typically > 400 tons assayed In-situ (using Cerenkov light)  Low energy data analysis  Separate 208 Tl & 214 Bi  Good measure of time variation Event isotropy  Low Energy Radioactivity These both yield concentrations of U and Th Still need fraction above energy threshold and inside volume

Bottom of vessel 2/3 way up Top of vessel MnOx HTiO MnOx HTiO Background Measurement  Radioassays

Background Measurement  Tail of `Cerenkov events’ inside D 2 O New technique: Rn `Spikes’ + Monte Carlo for Th and Na

Background Measurement  Misreconstruction of Events Into Volume from Outside Fit radial profile outside volume and extrapolate inside Total `internal’ + `external’ Cerenkov bkd < 14.7 events.

Background Measurement  Spallation Products Cosmogenic 16N most problematic… …but fewer than 3 events left after cuts.

Background Measurement  Neutrons Many potential sources…and they look exactly like NC events. Salt includes more backgrounds (eg 24 Na) but also some new handles

Background Measurement  `External’ Sources of Neutrons Photodisintegration from acrylic vessel and H2O radioactivity ( ,n) processes in acrylic (R/R AV ) 3 High Cl capture cross section allows direct fit for all neutron sources outside fiducial volume MC Radial pdfs for Signals and Backgrounds

Background Measurment  24 Na neutrons 24 Na: n capture on 23 Na leads to decay and neutrons… Sources: Recirculation Neck of acrylic vessel Calibration source activation Test by `activating’ Na in neck of vessel and elsewhere Z (cm)  = (x 2 + y 2 ) 1/2 (cm) Z (cm)

Background Measurment  Summary of Backgrounds

Signal Extraction Data sample Calibrated model for pdfs Measured backgrounds Now have: Maximum likelihood fit to R 3, cos  sun, and Isotropy(T) yields: (statistical uncertainties only)  Event Numbers Blind criteria removed `box opened’

Signal Extraction  Fit to Data Solar Direction Isotropy Radius (R 3 )

Signal Extraction  Flux Measurements To obtain fluxes, normalize by: Cut efficiencies Threshold and fiducial volume acceptance Cross sections Number of deuterons Livetime neutron capture efficiency

Internal neutrons Energy scale Resolution Radial accuracy Angular res. Isotropy mean Isotropy width Radial E bias Cer. bkds “AV” events Neutron capture Total Signal Extraction  Flux Measurements

SNO Phase II (Salt Phase)  Summary of Systematic Differences from Phase I Higher NC statistics Use of isotropy parameter to identify neutrons Extraction fit independent of CC/ES spectrum Higher E threshold, less dependence on bkd uncertainties Improved techniques for measuring background tails Better ID on external neutron sources Lower radioactive U, Th backgrounds Blind analysis

Signal Extraction  Further Systematic Checks Used independent approaches to nearly all elements: Alternate isotropy parameters Different reconstruction algorithms Various fiducial volumes and thresholds Data-based (muon follower) pdfs vs. Monte Carlo All results consistent within systematic uncertainties.

Phase II Results  Flux Measurements (units 10 6 cm -2 s -1 )

Phase II Results  Flux Measurements (units 10 6 cm -2 s -1 ) Using 8 B spectral information in fit Compare to D 2 O measurements:

Phase II Results  SNO Compared to Other Solar Expts.

Phase II Results:Mixing Parameters Maximal mixing ruled out at ~ 3 

Phase II Results:Mixing Parameters Maximal mixing ruled out at 5.4 

Physics Motivation Event-by-event separation. Measure NC and CC in separate data streams. Different systematic uncertainties than neutron capture on NaCl. NCD array as a neutron absorber. Detection Principle 2 H + x  p + n + x MeV (NC)  3 He + n  p + 3 H x n Array of 3 He counters 40 Strings on 1-m grid 440 m total active length NCD PMT SNO Phase III (NCD Phase)  3 He Proportional Counters Beginning ~November 2003

Future Measurements  Status Summary Antineutrino (D 2 O data) analysis under review Spectrum from Salt Phase Day/Night from Salt Phase hep neutrino analysis including salt data

Conclusions Phase I SNO results show clear appearance of non- e flavors Phase II first measurement of total flux without assumptions about shape of survival probability New precision has ruled out maximal mixing at high level Searches for MSW (matter) effect next high priority Phase III will add even further precision