CERN's LHCb collaboration reported on November 3 evidence of a particle decay predicted to occur roughly once in ten billion cases. The experiment near Geneva detected a signal for a neutral B meson turning into a muon and an antimuon. Cambridge and Oxford also announced the result, which reaches 3.2 sigma statistical significance but falls short of a confirmed discovery.
The particle, known as Bd, contains a beauty quark and a down antiquark. Muons resemble electrons but are heavier. According to CERN, measuring this exceptionally unlikely transformation can test the Standard Model because undiscovered particles could influence its frequency, even if the collider cannot produce those particles directly.
Researchers combined data from 2024 and 2025 with records collected between 2011 and 2018. CERN says the newer sample alone reaches 3.0 sigma. The upgraded detector records data at up to five times its earlier rate, while better particle identification and machine learning help separate the faint signal from other processes.
CERN says a joint LHCb and CMS analysis in 2015 suggested evidence for this decay, but subsequent updates did not confirm it. The new finding is the first evidence from a single experiment. The same analysis also improves measurements of the related Bs decay into a muon pair, a process already observed.
Cambridge says the results have not yet undergone peer review. They agree with Standard Model predictions and do not establish the existence of new particles. Researchers now need more data to reach the five-sigma discovery threshold. CERN says a further LHCb upgrade planned for the mid-2030s could sharpen these tests of fundamental physics.
Comments