Two sightings in Minnesota have set physicists buzzing about whether the first direct detection of dark matter has been made. If confirmed, it would mark the end of a decades-long search for the mysterious particles thought to make up as much as 85% of matter in the Universe.

But most agree that the signals are not statistically significant enough to be attributed to dark matter rather than to conventional particles.

The two events were caught in 2007 in super-cooled crystals of germanium and silicon in the underground Cryogenic Dark Matter Search II (CDMSII) experiment in the Soudan Mine in Minnesota. Last week, CDMSII scientists announced that they have seen candidates for the dark-matter particles known as weakly interacting massive particles (WIMPs), each with a mass of 30–60 gigaelectronvolts — roughly 30–60 times that of a proton.

But from the analysis, team scientists think that there is a 25% chance that both events might be false-positives caused by background radiation. Those odds are not good enough to claim a definitive detection of WIMPs, says Timothy Sumner, a physicist at Imperial College London. "Statistically, it's not compelling," he says.

"The best we could call it is a hint," adds John Ellis, a theoretical physicist at CERN, Europe's high-energy physics lab near Geneva, Switzerland. "An interesting hint."

The possible detection is the latest in a series of potential dark-matter sightings. In August 2008, an Italian-led satellite-based experiment known as PAMELA reported an excess of antielectrons (positrons) that could have stemmed from the annihilation of dark-matter particles. And in October 2009, NASA's Fermi Gamma-ray Space Telescope saw a haze of high-energy light in the centre of our Galaxy that could be a dark-matter signature.

The CDMSII result will now spur physicists at the Large Hadron Collider (LHC) at CERN to try to generate WIMPs in their collisions. "The LHC would see this very easily and relatively quickly," says Ellis — and could potentially produce a detectable WIMP signal by the end of next year.