"We have moved to a precision phase of the measurements." says Queen's University Professor Art McDonald, SNO Project Director through the first two phases of the project. "These measurements are essential to define a new theory of elementary particles required to explain finite neutrino masses and their ability to change types. Some of the simplest proposed theories have already been ruled out."
To accomplish the new measurements, the SNO Collaboration added 2 tonnes of high-purity table salt (NaCl) to the 1000 tonnes of heavy water at the heart of the detector, sited 2 kilometres underground in near Sudbury, Canada. Two-thirds of the electron-type neutrinos produced by nuclear reactions in the core of the Sun are observed to change to muon- or tau-type neutrinos before reaching the Earth. "These new solid results are obtained with a 'pinch of salt', providing three times better sensitivity to the muon and tau neutrinos." Says Professor Tony Noble, Director of the SNO Institute that administers the project on behalf of an international collaboration of 130 scientists from 15 institutions in Canada, the U.S. and the U.K.The observations in recent years that neutrinos change from one type to another, implying that they have mass, has led to great interest in the scientific community.
These new findings require a modification of the most basic theories for elementary particles and have provided a strong confirmation that our theories of energy generation in the Sun are very accurate. New experiments to provide further information on neutrino properties and the origin of the Dark Matter in the Universe are being developed. These include projects that could be sited in the new SNOLAB being developed near the SNO underground site. Such measurements could provide insight into fundamental questions such as why our Universe is composed of matter rather than anti-matter. The answers to such questions require a further understanding of elementary particle theory and further insight into the evolution of the Universe.
To pursue such questions, the Sudbury Neutrino Observatory is about to enter a third experimental phase with new sensitivity. Professor Hamish Robertson of the University of Washington, Seattle, US Co-spokesman and Interim SNO Director for this transition phase, says "We have developed a half-kilometre-long array of ultra-clean detectors to be placed in the heavy water after the salt is removed in September. These detectors are precision instruments that will give us further insight into neutrino properties."
Professor Nick Jelley of Oxford University, co-spokesman of the UK SNO Collaboration states, "As we have moved forward with ever increasing sensitivity, we are learning more about neutrinos and their place in the Universe. It is very exciting to be performing these ground-breaking measurements with our unique experimental sensitivity."
The new results from the Sudbury Neutrino Observatory (SNO) have been submitted for publication and are posted at http://www.
Notes for Editors:
Sudbury Neutrino Observatory
Image available here
The Sudbury Neutrino Observatory is a unique neutrino telescope, the size of a ten-storey building, 2 kilometres underground near Sudbury, Ontario planned, constructed and operated by a 100-member team of scientists from Canada, the United States and the United Kingdom. Through its use of heavy water, the SNO detector provides new ways to detect neutrinos from the sun and other astrophysical objects and measure their properties. For many years, the number of solar neutrinos measured by other underground detectors has been found to be smaller than expected from theories of energy generation in the sun. This had led scientists to infer that either the understanding of the Sun is incomplete, or that the neutrinos are changing from one type to another in transit from the core of the Sun.
The SNO detector has the capability to determine whether solar neutrinos are changing their type en-route to Earth, thus providing answers to questions about neutrino properties and solar energy generation.
The SNO detector consists of 1000 tonnes of ultra-pure heavy water enclosed in a 12-metre diameter acrylic-plastic vessel, which in turn is surrounded by ultra-pure ordinary water in a giant 22-meter diameter by 34-meter high cavity.
Outside the acrylic vessel is a 17-meter diameter geodesic sphere containing 9456 light sensors or photomultiplier tubes, which detect tiny flashes of light emitted as neutrinos are stopped or scattered in the heavy water. The flashes are recorded and analysed to extract information about the neutrinos causing them.
At a detection rate about 10 per day, many days of operation are required to provide sufficient data for a complete analysis. The laboratory includes electronics and computer facilities, a control room, and water purification systems for both heavy and regular water.
The construction of the SNO Laboratory began in 1990 and was completed in 1998 at a capital cost of $73M CDN with support from the Natural Sciences and Engineering Research Council of Canada, the National Research Council of Canada, the Northern Ontario Heritage Foundation, Industry, Science and Technology Canada, INCO Limited, the United States Department of Energy, and the Particle Physics and Astronomy Research Council of the UK. The heavy water is on loan from Canada's federal agency AECL with the co-operation of Ontario Power Generation, and the unique underground location is provided through the co-operation and support of INCO Limited.
Measurements at the SNO Laboratory began in 1999, and the detector has been in almost continuous operation since November 1999 when, after a period of calibration and testing, its operating parameters were set in their final configuration. Measurements from the initial phase with pure heavy water were reported in 2001 and 2002 and showed clearly that about two-thirds of the electron type neutrinos created in the Sun changed their type to muon- or tau-type neutrinos in transit to the Earth. This transformation appears to arise from a finite mass for neutrinos, a finding beyond the current Standard Model of Elementary Particles. The measurements of all three neutrino types showed very good agreement with the expected numbers of neutrinos generated in the Sun, confirming current theories of energy generation in the Sun.
Further background information can be found on the SNO website: http://www.
SNO Participating Institutions:
United Kingdom- Oxford University, University of Sussex, CCLRC, Rutherford Appleton Laboratory-Canada, Queen's University, Carleton University, Laurentian University, University of Guelph, University of British Columbia, TRIUMF Laboratory, United States-Lawrence Berkeley National Laboratory, Los Alamos National Laboratory, University of Pennsylvania, University of Washington, Brookhaven National Laboratory, University of Texas, Austin.
For further information:
Professor Nick Jelley, UK Co-spokesman
Oxford, England, UK
Professor David Wark, U.K. Co-spokesman
RAL/University of Sussex Sussex, UK
Prof. Art McDonald, SNO Director, on sabbatical
University Research Chair in Physics
Prof. Tony Noble, SNO Institute Director
Sudbury Neutrino Observatory Institute
Director of Communications
Sudbury Neutrino Observatory
Tel: 705-675-1151 Ext. 2202
Prof. Hamish Robertson, US Co-spokesman
Interim SNO Director
University of Washington
Seattle, Washington, USA
Prof. Eugene Beier, U.S. Co-spokesman
University of Pennsylvania
Philadelphia, PA, USA
Professor David Sinclair, Director of SNOLAB Development
Ottawa, Ont. Canada
PPARC Press Office
Public Relations, CCLRC Rutherford Appleton Laboratory
Paul de la Riva, Media relations officer
Department of Public Affairs, Laurentian University
Sudbury, ON, Canada
Web Address: http://www.
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