Canadian researchers uncover tool for hunting dark matter
Last Updated: Thursday, October 16, 2008 | 11:30 AM ET
CBC News
Researchers at the Sudbury Neutrino Observatory say they have developed a new technique in the search for dark matter, the invisible substance or group of substances that make up a large percentage of the universe.
The Picasso group, made up of researchers from Canada, the United States and Czech Republic, said the new method will clear out background noise from other particles to give detectors a better shot at finding dark matter signals.
Dark matter is an important part of our picture of the universe — its gravitational influence helps explain why stars at the edges of galaxies appear to move at the same speed as those near the centre, for example.
Because it does not absorb or emit light it is undetectable through direct means. Maps of dark matter have been produced, however, using its gravitational influence on light from distant stars to infer its presence.
While astronomers and physicists believe it is out there, the more vexing question has been: what exactly is it?
One group of candidates is called Weakly-Interacting Massive Particles, or WIMPS. These theoretical particles get their name because they only interact with two of the fundamental forces of nature: gravity and the weak nuclear force.
Because they ignore electromagnetism, WIMPS would be invisible to light or other waves of radiation, and because they ignore the strong nuclear force they would pass through atoms without detection.
Hope to detect particles
It is these particles the researchers at the SNOLab hope to detect, using a bubble chamber at the bottom of an old mine shaft in the underground facility in Sudbury, Ont. The deep underground location helps isolate the facility from larger particles from space like cosmic rays, while the chamber itself contains a sensitive super-heated liquid that, when WIMPS pass through it, records the passage as acoustic signals.
Unfortunately, the detector also finds alpha particles, the relatively common byproduct of radioactive decay.
That stumbling block may have been overcome, the researchers wrote in the New Journal of Physics, with the discovery of a subtle difference in the acoustic signals between alpha particles and WIMP-like particles. Like turning the dial of a radio to a different station, the researchers believe tuning out the alpha particle signals will give them a better shot at finding these WIMPs.
"When we looked at our calibration data taken with neutrons and compared them with our alpha background data we saw a peculiar difference which we attributed first to some detector instabilities or gain drifts in our electronics," said experiment spokesperson Viktor Zacek of the University of Montreal in a statement.
"However when we checked the data and refined the analysis the discrimination effect became even more pronounced," he said.
The technique could give the researchers a better chance at detecting the particles, and as a result, come closer to identifying dark matter.
Scientists believe dark matter makes up about 23 per cent of the stuff of the universe, with visible matter like stars and planets making up just four per cent. the rest of the universe is made up of the even more mysterious dark energy, which is responsible for the expansion of the universe.
Researchers from the University of Montreal, University of Alberta, Laurentian University, Queens University all contributed to the research.
