The SNO Neutrino Detector


The Sudbury Neutrino Observatory (SNO) is a water Cherenkov detector dedicated to investigate elementary particles called neutrinos. It was designed to provide revolutionary insight about the production of neutrinos in the core of the sun and to extend previous results from Kamiokande and SuperKamiokande by measuring three reactions of solar neutrinos.

SNO was designed to determine whether the currently observed solar neutrino deficit is a result of neutrino oscillations. The detector is unique in its use of heavy water as a detection medium, permitting it to make a solar model-independent test of the neutrino oscillation hypothesis by comparison of the charged- and neutral-current interaction rates.

 

The SNO detector was installed in a large cavity excavated at the 6800 foot level in the Creighton mine near Sudbury, Ontario. SNO used 1000 tonnes of heavy water contained in a 12 meter diameter acrylic vessel. Neutrinos reacted with the heavy water to produce flashes of light called Cherenkov radiation. This light was then detected by an array of 9600 photomultiplier tubes mounted on a geodesic support structure surrounding the heavy water vessel.

 
 

 


The detector was immersed in light (normal) water within a 30 meter barrel-shaped cavity excavated from the rock. Located in the deepest part of the mine, the overburden of rock shielded the detector from cosmic rays. The detector was operating in a very clean environment to reduce background radiation signals which would otherwise hide the very weak signal from neutrinos.

The motivation for the SNO experiment was to study the fundamental properties of neutrinos, in particular the mass and mixing parameters. The long distance to the solar source of neutrinos makes the search for neutrino mass sensitive to much smaller mass than can be studied with terrestrial sources.

Furthermore, the matter density in the sun is sufficiently large to enhance the effects of small mixing between electron neutrinos and muon or tau neutrinos. This experiment, when combined with the results of other experiments, will extend our knowledge of these fundamental particles, and as a byproduct, improve our understanding of energy generation in the sun.

The physics group at Carleton was involved in the design & operation of the water purification system, in data analysis, in detector calibration, and in R&D for the next generation neutrino detectors. The   principal investigators of the Carleton group were:

  1. David Sinclair  Also Director of the International Facility for Underground Science (SNOLAB)
  2. Alain Bellerive (CRC) as the Carleton group representative on the SNO Board.

David Sinclair (Fellow of the Royal Society of Canada) came from OxFord and founded the SNO group at Carleton. Cliff Hargrove (Emeritus Professor) is one of the experts on low energy background calibration. Prof. Hargrove was one of the first scientists involved in the SNO project back in the 1980's. Richard Hemingway (Honourary Research Professor) is an IPP Scientist with many years of experience in Collider Physics. He served on the OPAL council at CERN and the International Committee for Future Accelerators (ICFA). Alain Bellerive (Associate Professor) is a Canada Research Chair focusing on managing the data analysis activities. Peter Watson's interest was in the study of non-solar neutrino burst.  Kevin Graham (Assistant Professor) was also involved in man aspects of the SNO and SNOLAB projects.

The data analysis team was led by Alain Bellerive, Kevin Graham, and Richard Hemingway. Carleton has excellent technical support (one engineer and one chemist), several students and research assistants. Research associates, Feng Zhang and Khalil Boudjemline,  were based in at Carleton University and worked on  data analyses, optical and energy calibration, and Monte Carlo simulation.

Darren Grant (Ph.D. - graduated in 2004) did his M.Sc. building the D2O process degasser, and his work has contributed greatly to help support the water group on site. For his Ph.D. he was in involved in the optical calibration of SNO and signal extraction for the salt phase. Ferenc Dalnoki-Veress (Ph.D. - graduated in 2003) provided the same kind of support working on the radon problem and other issues of background; he developed the PCS calibration source. Gordana Tesic (Ph.D.) was  in charge of the program for the determination of the solar neutrino oscillation parameters and was the local run/data selection expert. Etienne Rollin (Ph.D.) was involved in detector development and search for hep neutrinos. Olivier Simard (Ph.D.) was n charge of the optical calibration and study spectrum distortion. Pierre-Luc Drouin (Ph.D.) was the  local C++ expert and worked on the CC-ES-NC signal extraction. Louise Heelan (M.Sc. - gradutated in 2005) looked for periodic behaviour in the solar neutrino flux.