Overview
- LHCb presented results on Tuesday that show 3.2σ evidence for the B0 (Bd) → μ+μ− decay, the first time a single experiment has reached the evidence threshold for this process.
- The decay was observed at a rate of about one in 10 billion B0 decays and the measured frequency agrees with predictions from the Standard Model.
- The signal was isolated by combining 2024–2025 data from the upgraded detector with earlier 2011–2018 datasets and using machine‑learning methods to reduce background.
- At 3.2σ the result is classified as evidence and falls short of the 5σ level needed for a discovery, so the collaboration says far more data and planned mid‑2030s upgrades or a future collider will be needed to reach definitive results.
- The analysis was led by an international team with significant UK technical contributions, but reports that UK Research and Innovation withdrew a planned funding share raise questions about the UK’s future involvement in upgrades and hardware supply.