The key facts
- LHCb has obtained evidence of the decay of a neutral B meson into a muon and an antimuon; the expected probability is about one case per 10 billion decays.
- The result is based on proton collision data at 13.6 TeV recorded by the upgraded detector in 2024–2025, combined with earlier measurements.
- Discovery status has not yet been reached: the authors call the result evidence and await additional data; the measurements are consistent with the Standard Model.
Evidence, not a discovery
Physicists of the LHCb collaboration at the Large Hadron Collider have obtained evidence of an extremely rare decay of a neutral B meson into a muon and an antimuon. According to Standard Model calculations, such an outcome is expected in roughly one out of 10 billion decays of this particle. The preprint of the study has been posted on the arXiv portal, reports Gazeta.Ru.
Why this decay matters
Muons are similar to electrons but considerably heavier. The decay of a B meson into just two such particles is of particular interest to physicists: its low probability makes the process sensitive to possible deviations from the existing theory. For the analysis, the researchers used proton collisions at an energy of 13.6 teraelectronvolts, recorded by the upgraded LHCb detector in 2024–2025, and then combined these results with earlier measurements from the experiment.
What comes next
The signal obtained so far is not sufficient to declare a full-fledged discovery: the authors call the result evidence of the decay and note that additional data must be accumulated to reliably separate the signal from background and statistical fluctuations. At the same time, the team refined the probability and the effective lifetime of another rare decay — that of the strange B meson into a pair of muons. All the measurements presented are consistent with the predictions of the Standard Model: the work offers a new way to test the fundamental theory, but so far does not point to the detection of an unknown particle or new physics.
