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A potential chink in physicists’ understanding of fundamental particles and forces now looks more real. New measurements confirm a fleeting subatomic particle called the muon may be ever so slightly more magnetic than theory predicts, a team of more than 200 physicists reported this week. That small anomaly—just 2.5 parts in 1 billion—is a welcome threat to particle physicists’ prevailing theory, the standard model, which has long explained pretty much everything they’ve seen at atom smashers and left them pining for something new to puzzle over.

“Since the 1970s we’ve been looking for a crack in the standard model,” says Alexey Petrov, a theorist at Wayne State University. “This may be it.” But Sally Dawson, a theorist at Brookhaven National Laboratory, notes the result is still not definitive. “It does nothing for our understanding of physics other than to say we have to wait a little longer to see if it is real.”

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