Particle caught flip-flopping

D meson’s switch between matter and antimatter could help uncover new particles

A particle with an identity crisis could provide the next big discovery at the world’s largest particle accelerator. The D meson has been caught in the act of flipping between matter and antimatter, researchers report online March 5 in Physical Review Letters.

D mesons, like other mesons, are short-lived particles that emerge from the shrapnel of proton collisions at CERN’s Large Hadron Collider outside Geneva. All of these particles decay within tiny fractions of a second. But four mesons, including the D, occasionally do something strange first: They become antiparticles. In the same vein, anti-D mesons can switch and become mesons before they decay. While experimenters have observed B, strange B and K mesons exhibit this shifty behavior, this is the first time physicists have seen D mesons that start as matter end up decaying as antimatter, and vice versa.

The next step, says Syracuse University physicist Steve Blusk, one of about 600 members of the team that made the discovery, is to compare the number of D meson decays with the number of anti-D meson decays. Those numbers should be equal, but physicists are hoping that one number is slightly larger than the other, Blusk says, because that would mean an undiscovered particle interferes with the D meson’s oscillations.

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