After 40 years of searching, physicists find evidence for an ultrarare particle decay

The Quick Take

Physicists at CERN report that they've detected evidence of a rare meson particle decay (B⁰→ µ⁺µ⁻) that occurs when the meson's beauty quark annihilates with a down-type quark. The pair decays into a muon and antimuon, which are particles similar to electrons. Because evidence for this decay helps test theoretical predictions from the Standard Model, physicists have been waiting for it since 1984,