UK physicists report first evidence of ultra-rare beauty particle decay at CERN

Physicists from the University of Warwick, working within a UK-led collaboration, have announced the first observation of an extremely rare decay of a beauty particle at CERN’s Large Hadron Collider. The decay, in which a beauty meson transforms into a pair of muons (denoted (B_d \to \mu\mu)), is predicted to occur in roughly one out of every ten billion beauty particles produced.

The finding comes from data collected by the upgraded LHCb detector, which now records collisions at up to five times its previous rate. Researchers combined new data from 2024-2025 with earlier runs spanning 2011-2018 and applied machine-learning techniques to isolate the faint signal from background noise.

"This result showcases the extraordinary capabilities of LHCb to probe nature at the fundamental level," said Professor Tim Gershon, who leads the LHCb experiment at Warwick. He added that the project, driven by UK physicists, will continue with an upgrade planned for the 2030s to increase data-collection capacity.

The statistical significance of the observation is 3.2 sigma, sufficient to be classified as evidence but below the five-sigma threshold required for a formal discovery. The measured decay rate aligns with predictions of the Standard Model, narrowing the parameter space for potential new physics.

Dr. Harry Cliff, an Ernest Rutherford Fellow at the University of Cambridge who headed the analysis, noted that the observation confirms a long-standing search target and opens further opportunities to explore phenomena at the sub-zeptometer scale.

The United Kingdom contributed major components to the detector upgrade, including the silicon Vertex Locator positioned close to the LHC beams and the RICH system used for particle identification. A further upgrade in the 2030s aims to increase data-collection rates by an additional factor of five.