After 40 years of searching, physicists find evidence for an ultrarare particle decay
Physicists at CERN have confirmed evidence of an extremely rare particle decay, B⁰→ µ⁺µ⁻, after 40 years of research. This discovery helps validate theoretical predictions of the Standard Model of particle physics.
Why it matters
Confirming these rare decays is essential for testing the limits of the Standard Model and potentially identifying new physics beyond current scientific understanding.
edited by Lisa Lock , reviewed by Robert Egan
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Add to Preferred Sources Example Feynman diagrams for the B⁰→ µ⁺µ⁻ decay. Credit: arXiv (2026). DOI: 10.48550/arxiv.2611.00230 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, when it was first theorized.
The team details the measurements along with those of another slightly less rare decay in a recent paper posted to the arXiv preprint server.
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