Searching for wimps

by BBC News Online's Damian Carrington

The search for the 99% of the Universe that appears to be missing is well on track, said British scientists investigating one of science's greatest mysteries.

Their experiments at the bottom of the deepest mine in Europe have begun to get very promising results, but they say they must check other possible explanations before they can definitely announce they have located the missing matter.

Results unexpected

Only 1% of the universe is visible

"The results are unexpected and very exciting - so far we have no other explanation," said Dr Neil Spooner, speaking at the British Association's Festival of Science.

He is part of the UK Dark Matter Consortium who are hunting for sub-atomic particles called WIMPs, Weakly Interacting Massive Particles. These have never been detected but astronomical and particle physics theory predicts they exist and could account for the Universe's lost mass.

Only 1% of universe visible

Astronomers know there is much more mass in the Universe than can be seen by the way galaxies rotate under the influence of gravity from hidden matter. Only one percent of the Universe is visible and just 10% of our own galaxy can be spotted.

But searching for WIMPs is not easy. Billions of the particles are thought to continuously flood through the Earth (on people) but only one in a million will crash into an atom's nucleus and give off a tell-tale signal.

Underground experiments

Even worse is that cosmic rays from space can produce the same tiny flashes of light but in far greater numbers. That is why the astronomers carry out their experiments 1,100m under the Earth at Boulby potash mine in North Yorkshire - the rock above shields their detectors from the cosmic rays.

Flashes have now been detected but Dr Spooner said: "We must rule out any backgrounds signals that are currently unaccounted for, such as impurities on the surface of our crystal detectors."

Tests so far show no evidence of this problem.

Results reproduced

A French laboratory has provided extra encouragement by getting similar results but with different technology.

Dr Spooner said that two new types of detectors, hundreds of times more sensitive, will help settle whether their results have been artefacts or whether they have really found the hidden 99% of the Universe.