A common table commodity that people sprinkle on their food every day is the main ingredient in new measurements by scientists at the Sudbury Neutrino Observatory (SNO). In a presentation on Sunday September 7th, at TAUP2003, a major scientific conference in Seattle, Washington, new measurements were reported that strongly confirm the original SNO results announced in 2001 and 2002 that solved the "Solar Neutrino Problem" and go much further in establishing the properties of neutrinos that cause them to change from one type to another in transit to the Earth from the Sun.
"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.sno.phy.queensu.ca/
The web site for the TAUP 2003 conference is: http://int.phys.washington.edu/taup2003/
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