The LHCb Collaboration reports the first evidence from a single experiment for the rare decay B⁰ → μ⁺μ⁻, in which a neutral B meson produces a positive muon and a negative muon. The collaboration says the measurements agree with Standard Model expectations. LHCb’s abstract describes the result as evidence; ScienceAlert reported a significance of 3.2σ.
The Run 3 data behind the result
LHCb used 18 fb⁻¹ of proton-proton collision data collected at 13.6 TeV with its Upgrade I detector during 2024–2025. The analysis combines those Run 3 results with LHCb results from Run 1 and Run 2. The collaboration’s abstract gives the Run 3 dataset and collision conditions.
The same work reports the most precise measurements to date of the B⁰ₛ → μ⁺μ⁻ branching fraction and effective lifetime. Those are measurements of a related decay, distinct from the evidence for B⁰ → μ⁺μ⁻.
A related B⁰ₛ result
A separate CMS event display visualizes a candidate B⁰ₛ → μ⁺μ⁻ event through reconstructed particle tracks. It offers a look at how a candidate collision event can be represented; it is CMS event visualization, separate from LHCb’s analysis.
The Run 3 dataset supplies the new evidence, while the B⁰ₛ measurements address a separate decay channel.
