Elementary particle

Collider data hint at unexpected new subatomic particles

LHCb experiment
WEIRD DECAYS Something funny may be going on in certain particle decays measured in the LHCb experiment in Geneva (above). A new measurement has now added to scientists’ suspicions.

A handful of measurements of decaying particles has seemed slightly off-kilter for years, intriguing physicists. Now a new decay measurement at the Large Hadron Collider in Geneva has amplified that interest into tentative enthusiasm, with theoretical physicists proposing that weird new particles could explain the results. Scientists with the LHCb experiment reported the new result on April 18 in a seminar at the European particle physics lab CERN, which hosts the LHC.

“It’s incredibly exciting,” says theoretical physicist Benjamin Grinstein of the University of California, San Diego. The new measurement is “a further hint that there’s something new and unexpected happening in very fundamental interactions.”

Other physicists, however, are more cautious, betting that the series of hints will not lead to a new discovery. “One should always remain suspicious of an effect that does not show up in a clear way” in any individual measurement, Carlos Wagner of the University of Chicago wrote in an e-mail.

Taken in isolation, none of the measurements rise beyond the level that can be explained by a statistical fluctuation, meaning that the discrepancies could easily disappear with more data. But, says theoretical physicist David London of the University of Montreal, there are multiple independent hints, “and they all seem to be pointing at something.”

The measurements all involve a class of particle called a B meson, which can be produced when protons are smashed together in the LHC. When a B meson decays, it can produce a type of particle called a kaon that is accompanied either by…