The LHCb team at CERN reported evidence of a rare particle decay on November 3, 2026. The new analysis points to a B0 beauty particle turning into two muons, according to the collaboration.
The result fits the Standard Model, the theory of known particles and the forces between them, LHCb says. It limits some theories of new particles. However, it falls short of the bar needed to claim a discovery.
Rare particle decay still needs confirmation
LHCb reports a statistical significance of 3.2 sigma from new and past data. Sigma measures how far a result lies from what background processes alone would suggest. CERN says confirmation requires five sigma.
CERN says this rare particle decay is expected in roughly one out of every 10 billion decays of this particle. The B0 particle contains a beauty quark or its antiparticle, CERN says. Its decay products are a muon and an antimuon. Muons resemble electrons but have more mass, CERN says.
The analysis is a preprint submitted to Physical Review X, according to the paper. It uses proton collisions recorded in 2024 and 2025, along with earlier results. The new sample measures 18 inverse femtobarns, a standard measure of collision data.
An upgraded detector separates the signal
UK Research and Innovation says the upgraded detector can record data at up to five times its earlier rate. Better tools to identify particles, along with machine learning, help the team filter out other processes.
UKRI says UK teams helped build the detector and led the analysis. Their silicon tracking system sits just five millimeters from the beams. It helps find where particles form and decay.
Why physicists are looking for this decay
The LHCb paper says particles too heavy to produce directly can still affect the behavior of known particles. Precise tests of how particles decay can thus probe what lies beyond the reach of direct searches.
The paper traces the search for this decay to the CLEO experiment in 1984. CERN says a joint LHCb and CMS analysis reported evidence in 2015, but later updates did not confirm it.
CERN says further research will aim to reach the five-sigma threshold. LHCb also plans a further detector upgrade in the middle of the next decade to collect more data.
Sources: LHCb paper, LHCb, CERN, UKRI
