Once again, physicists have not found particles of dark matter—the mysterious stuff whose gravity holds galaxies together. Researchers working with the XENON100 particle detector in the subterranean Gran Sasso National Laboratory in central Italy report today that 100 days' worth of data taking turned up three events that could be dark matter particles smacking nuclei in the 62 kilograms of liquid xenon in their detector. But the scientists expect roughly two false positives from ordinary particles, so the chances are that all three events are "background," the team explains in a paper submitted to Physical Review Letters. The results show that other claimed dark-matter sightings were also spurious, the authors say. Physicists remain hopeful that bigger detectors will provide proof positive of dark-matter particles within the next few years.
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