Queen’s University, Kingston, ON, Canada The Ryan Martin, Queen’s University, Kingston, ON, Canada 8th January 2007- EPFL

The SNO Collaboration Canada: USA: UK: Portugal: Queen’s, Carleton, Guelph, Laurentian, University of British Columbia, TRIUMF USA: University of Pennsylvania, Los Alamos National Lab, Lawrence Berkley National Lab, University of Washington, Brookhaven National Lab, University of Texas, University of Louisiana, Indiana University South Bend UK: Oxford University Portugal: Lisbon Technical Institute

Outline Solar Neutrinos The Solar Neutrino Problem Neutrino Oscillations The Sudbury Neutrino Observatory Overview of the salt phase The NCD phase SNOLAB, SNO+ and the future

Solar Neutrinos Neutrinos are created in the fusion reactions that power the Sun SNO is sensitive to 8B neutrinos from the p-p reaction chain in the Sun (>7MeV) pep neutrino flux has the smallest uncertainty

The Solar Neutrino Problem Detection of solar neutrinos first proposed by Bahcall Homestake experiment (Ray Davis) shows first signs of solar neutrino deficit Until 2001, other experiments (SAGE, GALLEX) also see a solar neutrino deficit Experimental evidence for the “solution” provided by Super Kamiokande in 1998 (atmospheric neutrino oscillations)

Neutrino Oscillations First proposed by Pontecorvo Neutrinos are quantum states, flavour and energy eigenbasis are different The PMNS matrix: Vacuum Oscillations (two flavours):

The Solar Survival Probability The survival probability is energy dependent due to the MSW effect (yet to be observed experimentally) SNO’s energy window not well positioned for observing MSW

The Situation before SNO Long standing deficit of electron flavour neutrinos coming from the Sun Need for an experiment that can measure the total flux of solar neutrinos and verify flavour-conversion The energy spectrum of solar neutrinos is yet unmeasured

The SNO Detector Heavy Water (D2O) Cherenkov detector 2km underground (6000mwe) in active nickel mine 12m diameter Acrylic Vessel (AV) 9000 PMTs on 18m diameter geodesic structure (PSUP) Surrounded by ultra-pure light water to shield from rock

The INCO mine and the clean lab

The Heavy Water reactions SNO is sensitive to three different neutrino reactions in Heavy Water: Charged Current (CC): Only electron flavour Strong Energy Correlation Neutral Current (NC): All flavours Neutron capture on D releases gamma that compton scatters electron Elastic Scattering (ES): Mostly electron flavour Strong directional sensitivity, low statistics

The Three Phases of SNO Phase I: Pure D20 Phase II: Salt (NaCl) Measurement of all three reactions, but NC signal can only be extracted with “Energy Constrained” fit Phase II: Salt (NaCl) Neutron capture cross-section increased as well as energy released from capture (2.5 gammas on average) The increase in isotropy of Cherenkov light from NC significantly increases the statistical separation between CC and NC (energy unconstrained) Phase III: The Neutral Current Detectors Designed to independently measure the NC flux Addition of 40 3He proportional counters to count neutrons Ended November 28th 2006 !

SNO Calibration About 20% of SNO time is devoted to calibrations A manipulator system allows for various sources to be moved along x-y-z in the detector: Laser Ball (optical and reconstruction) 16N (energy)-tagged gamma 252Cf (neutron detection efficiency)-fission

SNO Monte-Carlo The detector is fully modeled by Monte Carlo (SNOMAN) The Monte Carlo is extensively tested with calibration data Monte Carlo verification then allows for an accurate estimate of systematics

Basic Data Acquisition and Cleaning in Salt Phase Triggered events are recorded (timing and position of PMTs that fired) Low level data cleaning (instrumental background, pathological events) Event reconstruction (position and direction of Cherenkov cone) Observables calculated (Event energy) High level data cleaning (fiducial volume, Cherenkov characteristics)

Signal Extraction in Salt Phase The signal extraction is performed with an extended maximum log-likelihood fit Probability Density Functions (pdfs) are generated for each observable and signal (by Monte Carlo) Observable in salt phase: Event direction Isotropy Radial Position Energy Signals and Backgrounds in salt phase: NC, CC, ES (signals!) External neutrons Internal neutrons (indistinguishable from NC)

Cos(θsun) Best handle on ES signal Slight sensitivity to CC

β14 (Isotropy parameter) NC signal is more isotropic and this observable places the strongest constraint on it

Radial Distribution Extracting external neutron backgrounds Acrylic Vessel (AV) acts as a neutron sink on internal neutrons

Energy Reconstructed energy of the event is based on the number of hit PMTs Not constraining the CC energy shape allows one to measure it!

Results from Salt Phase Total Flux Energy Spectrum Mixing Parameters: -Δm2= (8 ± 0.5) x10-5 eV2 θ = (33.9 ± 2.3)° (With KAMLAND data!)

The Neutral Current Detectors (NCDs) Neutron Alpha

NCD observables: Energy ADC charge of NCD pulses is converted into energy spectrum (scaled from 210 Po peak) An “energy fit” can be performed to extract neutron signal: Do not know the background shape Have to limit possible shapes under the neutron peak

QGF PSA Pulse Shape Analysis (PSA): the idea to use pulse shapes to discriminate between neutrons and alphas Queen’s Grid Fitter (QGF): a library of neutrons and alpha pulses is created from calibration and 4He data: Data pulses are fit and the best neutron and best alpha chi-squared are determined Currently, used as a cut (good neutron, bad alpha), before doing energy fit Future (?), could be used as a pdf together with energy

Results from QGF (used as a data-cleaning cut) When used as a 2D-cut: 76% of neutrons pass 16% of alphas pass 32% of WE pass Signal/Background improves by factor of 5

The Future of SNO After 7 years of successful data-taking, SNO is currently being dismantled In the near future, publication of NCD results In the long(er) term, combined analysis of the three phases The NCDs are currently being “un-deployed”, in preparation for the Heavy Water extraction SNO has demonstrated the INCO site to be a good candidate for future low background experiments

The SNO space is being expanded into a international low background facility for experiments on: Direct Dark Matter Detection Neutrino-less Double Beta Decay Geo-Neutrinos Low-Energy Solar Neutrinos

SNO+ The only thing that we don’t own is the heavy water! Why not keep using everything else?! SNO+: Filling the Acrylic Vessel with liquid scintillator Can use the PMT and most of the electronics already in place

SNO+ Physics Low energy solar neutrinos (pep), can test MSW effect on spectrum Geo neutrinos (more events than KAMLAND) Reactor neutrinos (medium baseline) Could dope the scintillator with double-beta decay isotopes (SNO++, kiloton experiment!)

Summary SNO has shown that the solar model prediction was correct after all Strong constraints are now placed on the solar mixing angle The MSW effect still remains to be observed (spectrum or day-night effect) The techniques for maintaining a clean underground lab are now well developed Bright future for the subterranean part of Sudbury!

The End!