Latest SNO Results from Salt-Phase Data and Current NCD-Phase Status Melin Huang ● Introduction ● Results of Salt Phase (Phase II) ● Status of NCD Phase (Phase III) University of Texas at Austin on behalf of the SNO Collaboration

After Six Solar Experiments 3 Gallium (Radiochemical): SAGE/GALLEX/GNO Chlorine (Radiochemical): Homestake Kamiokande + Super-Kamiokande (Water Cerenkov)

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

1700 tonnes Inner Sield light water 5300 tonnes Outer Shield light water Support structure for 9500 PMTs concentrators 12m diameter acrylic vessel Norite rock Urylon liner and Radon Seal Vectran support ropes Control room 1000 tonnes heavy water 2090 m to surface 10^5 m to upper atmosphere 10^11 m to Sun 10^20 m to Galactic center The SNO Detector

e + d  p + p + e  C Q = MeV good measurement of e energy spectrum some directional info  ( 1 – 1/3 cos  ) e only Neutrino Reactions in SNO x + d  x + p + n NCNC NCNC Q = MeV measures total 8 B flux from the Sun all types x + e   x + e  ESES low cross section (  few events )  mainly sensitive to e, some  and   strong directional sensitivity Charged Current Neutral Current Elastic Scattering

CC/NC = 1 & CC/ES = 1 means No Neutrino Oscillation CC/NC Other neutrino types Implication: Recall: Testing Neutrino Oscillation – Inclusive Appearance Note: This technique is Independent of solar model !!! Advantage :Cross section uncertainties canceled for CC/NC

Neutron Detection Methods: Phase I (Nov 1999 – Apr 2001) : Neutron capture on deuterium in pure D 2 O: Lower neutron sensitivity, Poor discrimination between neutrons & electrons Phase II (Jun 2001 – Oct 2003) : Neutron capture on Cl using NaCl in D 2 O: very good neutron sensitivity, Better neutron-electron separation Phase III (Nov 2003 – Dec 2006) : Neutron capture in He proportional counters in D 2 O: Good neutron sensitivity, Great neutron-electron separation Three Phases of SNO

SNO Phase II (Salt Phase)  Advantages of NaCl: Capture Efficiency 2 tons of NaCl added June 1, 2001 The volume-weighted neutron detection efficiency: 40.7% in Salt Phase and 14.4% in Phase

SNO Salt Phase  Advantages of NaCl: Event Isotropy  multiplicity means PMT hit pattern for neutron events more isotropic than for single Cerenkov electrons Pl: legendre polynominal of order l : angle between PMTs i and j N : total # of triggered PMTs in the event

SNO Phases I & II ( MC pdfs for signal extraction) Phase I Phase II Phase I Phase II

Phase I Phase II SNO Phases I & II ( MC pdfs for signal extraction) MC pdfs are modeled based on several different calibration sources

Data Processing (Phase II – Salt Phase) 4772 candidates (~ 7 x 10^-6 triggered events) (1 hit PMT ~ 0.12 MeV)

Background Measurement (Phase II – Salt Phase) The distributions of high-level cut parameters Instrumental events Primarily U and Th chains+ 24 Na in Salt Phase Cherenkov events inside signal box Low Energy Radioactivity (in-situ/ex-situ) Misreconstruction neutrino events Other Backgrounds: ● Cosmic-ray muon ● Atmospgeric neutrino ● (alpha, n) process ● natural fission ● anti-neutrino

Signal Extraction  Fit to Data

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

Constraints on Mixing Parameters All solar neutrino experiments only All solar neutrino experiments and KamLAND 766 ton-year data (assuming CPT invariance) SNO I & II Maximal mixng ruled out at ~5.3

SNO Phase III (NCD Phase)  3 He Proportional Counters Array of 3 He counters 40 strings on 1-m grid 400 m total active length Neutrino enters D 2 O Interacts with deuterium to produce neutron Neutron wanders (ms) Neutron captures on NCD (or D 2 O) Production data taking began Dec 2004

SNO Phase III (NCD Phase)  Physics Motivation---Energy Spectrum CC and NC separation in pure D2O had big covariances (>90% correlations) Salt phase broke covariance with isotropy, but additional neutrons dilute CC signal Third phase has best of both worlds 3 He (`NCD’) counters remove neutrons from CC -- Independently calibrate remainder Event-by-event separation – measure CC & NC in separate data streams Different systematic uncertainties than neutron captures in Phase I & II small

SNO Phase III (NCD Phase)  NCD Event Pulse Shapes neutron with p-t track  wire De-logged current Time (microseconds) neutron with p-t track || wire De-logged current Time (microseconds)  track  wire De-logged current Time (microseconds) Current preamplifiers allow pulse shapes to be digitized for particle identification. alphas come from Th & U decay chains

SNO Phase III (NCD Phase)  NCD Pulse Energy & Electronic Parameter Calibrations ● Goal: Separation of background alpha events from physics neutron events ● Calibrations: -- pulse energy from shaper ADC information -- time constants of all effective low pass filters and high pass filters -- time constants used for describing dispersion of a pulse -- characteristic logarithmic amplifier (logamp) parameters Delay line NCD Simplified Electronic System

 NCD Pulse Energy & Electronic Calibrations (Preliminary Results) SNO Phase III (NCD Phase) ADC Shaper Bin Pulse Amplitude neutron peak (764 KeV) ~149 ADC bin proton edge (191 KeV) ~48 ADC bin energy vs ADC bin Blue: simulated Black: data Energy Calibration Logamp Parameter Calibration Time Constant Extraction (No Logamp) Time Constant Exatrction (in Multiplexer/Logamp) Pink: data Black: simulated

SNO Phase III (NCD Phase)  NCD Neutron Pulse Fits (Preliminary Results) ● Neutron energy close to neutron energy peak ● Alpha pulses still on going

SNO Phase III (NCD Phase)  NCD Neutron Calibration (Preliminary Results) Calibration Sources: ● Americium-Beryllium (AmBe) : ● Californium (252Cf): Generate 3 to 4 neutrons per fission

Conclusions Salt allowed enhanced NC capture and better separation between neutrons and electrons Phase II first measurement of total flux without assumptions about shape of survival probability -- Results are consistent with neutrino oscillation with Large-Mixing Angle parameters -- New precision has ruled out maximal mixing at high level Phase III analysis is on-going