New results have come in from the Xenon100 experiment, a tub of cryogenically cooled liquid xenon buried 1400 metres down a mine at the Gran Sasso National Laboratory near L'Aquila, Italy that show no sign of WIMPs, or weakly interacting massive particles, the still-theoretical particles thought to make up the invisible majority of the universe's mass, a direct challenge to physicists who believe dark matter is made up of WIMPs, particles that carry mass but, as their name suggests, rarely interact with other particles. The project's previous results, presented over a year ago and based on just 100 days of data, came up empty.
"We have essentially set the most stringent limits of any other experiment" for WIMPs with masses heavier than 8 gigaelectronvolts (GeV), said Antonio Melgarejo of the Xenon team, which will keep looking. The next generation of the experiment, called XENON1T, should start construction this year.
The standard model was confirmed by the discovery of the Higgs boson this month, but it still doesn't explain dark matter. In supersymmetry extensions of the Standard Model, every standard particle has a heavier "superpartner" particle, one of which could be a WIMP.
"We are starting to explore the region of supersymmetry," Melgarejo says. "It definitely imposes a big problem."* . Elsewhere, detector called LUX (Large Underground Xenon) will start operation at a mine in South Dakota, and promises to be 10 times as sensitive as previous searches.
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