LHCb reports first evidence of rare beauty meson decay

The LHCb collaboration has reported the first evidence from a single experiment for the exceptionally rare decay of a neutral beauty meson into two muons, after a search lasting more than four decades. The result, with a statistical significance of 3.2 sigma when combined with earlier LHCb data, falls short of the five-sigma threshold used to claim a discovery. The decay, written B⁰→μ⁺μ⁻, occurs when a short-lived particle containing a beauty quark transforms into two muons, heavier relatives of electrons. The process is expected to happen only about once for every 10 billion beauty particles, making it difficult to distinguish from the far larger background of other particle interactions. LHCb’s new data alone produced a significance of 3.0 sigma, according to the collaboration’s reported results. Combining those data with earlier measurements raised the significance to 3.2 sigma. The result is consistent with the Standard Model, the framework describing known fundamental particles and their interactions; it does not establish the existence of new particles or forces. The collaboration measured the decay’s branching fraction, or the proportion of particles that follow this...