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

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

2. The SNO Collaboration • Canada: • 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

3. 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

4. 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

5. 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)

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

7. 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

8. 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

9. 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

10. The INCO mine and the clean lab

11. 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

12. The Three Phases of SNO • Phase I: Pure D20 • 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 !

13. 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

14. 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

15. 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)

16. 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)

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

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

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

20. 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!

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

22. The Neutral Current Detectors (NCDs) Neutron Alpha

23. 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

24. 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

25. 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

26. 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

27. 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

28. 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

29. 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!)

30. 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!

31. The End!