LHCb finds first evidence of extremely rare decay
The measurement opens a new test of the Standard Model, but is not yet a discovery of new physics.
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Researchers from the LHCb experiment at CERN have found the first evidence of an extremely rare decay of a neutral beauty particle into two muons. The statistical significance is 3.2 sigma: according to the universities involved, enough to speak of evidence, but not enough to reach the usual five-sigma discovery threshold.
According to the Standard Model, the decay of a Bd particle into two muons should occur approximately once in every ten billion beauty particles. According to the universities involved, these are particles created in collisions in the Large Hadron Collider that exist for an average of roughly 1.5 trillionths of a second.
For the analysis, the researchers combined new data from 2024 and 2025 with measurements from earlier periods between 2011 and 2018. According to those universities, machine learning and improved methods for identifying particles helped extract the very weak signal from billions of collisions.
The result is consistent with the predictions of the Standard Model, the current theory of elementary particles and their interactions. Precisely because the decay is so rare, a more accurate measurement could later reveal whether unknown particles or forces of nature influence the likelihood of the decay.
The term ‘zeptoverse’ refers to distances of around a zeptometre, one billionth of a trillionth of a metre. It is not a new universe, but a term for a still barely explored range of particle physics.
The universities involved stress that further data is needed. According to the universities involved, five sigma is generally regarded in particle physics as the threshold for a discovery; this measurement is still below it. Follow-up measurements could help test existing theories further.
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The central claims appear in the publications of the universities involved. The text explicitly distinguishes between evidence and a discovery.
- confirmed LHCb found the first evidence of the decay of a neutral beauty particle into two muons. — The University of Manchester and the University of Birmingham describe this result. source
- confirmed The statistical significance is 3.2 sigma. — The University of Manchester gives the figure as 3.2 sigma. source
- confirmed According to the Standard Model, the decay is expected to occur approximately once in every ten billion beauty particles. — This is stated in the publications from Manchester and Birmingham. source
Editor's note
The measurement was announced today and comes from the LHCb experiment. The results are evidence of a rare decay, not a confirmed discovery of new particles or forces of nature.Sources
- Manchester physicists step closer to the ‘Zeptoverse’ after 42-year particle search — University of Manchester
- Physicists find evidence of nature’s rarest particle decays — University of Birmingham
- Physicists knock at the door of the zeptoverse — University of Cambridge
More on this in Dutch media
- NU.nl — „cern lhcb”
- De Telegraaf — „cern lhcb”
- AD — „cern lhcb”