Science and space / November 5, 2026
A nearly impossible decay brings CERN closer to exploring the zeptoverse
The LHCb experiment found evidence of a transformation that occurs roughly once in ten billion decays. The result opens up a new way to study tiny scales, although it does not yet reveal any unknown particles or forces.
For every ten billion B⁰ mesons that decay, just one is expected to produce a muon and an antimuon. That exceptionally rare transformation is what the LHCb experiment at CERN has found evidence for the first time using data from a single experiment.
The result, presented on November 3, 2026, is a new tool for testing the known rules of physics and peering into distances scientists call the zeptoverse. The name sounds like something out of a science-fiction movie, but it is not a parallel universe: it is a way of talking about extraordinarily small scales.
A signal amid an awful lot of noise
The B⁰ meson is an unstable particle containing a beauty quark and an antiquark. It lasts a tiny fraction of a second before transforming into other particles. In the decay studied, the result is a muon and its antiparticle; the muon resembles an electron, but is heavier.
To find the signal, the team analyzed collision data recorded by the LHCb detector during 2024 and 2025. The experiment’s upgrade and the use of machine learning helped distinguish possible events from an enormous number of background signals.
When those data were combined with earlier records collected between 2011 and 2018, the signal reached a significance of 3.2 sigma. That is enough to call it evidence, but it falls short of the five-sigma threshold usually required to declare an observation in particle physics.
It is also worth qualifying “for the first time”: in 2014, a joint analysis by the CMS and LHCb experiments had already found indications of this same decay. What is new is that a single experiment has now gathered evidence on its own.
What does this have to do with the zeptoverse?
A zeptometer is one sextillionth of a meter: a decimal point followed by twenty zeros before the one. At those distances, phenomena we do not yet know about could exist.
The physicists did not directly observe an object of that size. The idea is subtler: other particles can influence a decay through quantum effects, even if they are too heavy to be produced directly in collisions. Measuring how often this process occurs with precision could reveal discrepancies with current predictions or limit what kinds of new particles are possible.
For now, the result agrees with the Standard Model, the theory that describes known particles and several of their interactions. Nor does it mean that dark matter has been discovered: understanding what it is made of remains one of the questions motivating the search for new physics.
What comes next
The study has not yet been peer reviewed, and more data will be needed to strengthen the signal and measure it more precisely. For those investigating fundamental particles, the advance offers a more demanding test of their theories; for everyone else, it is a good reason to be skeptical of headlines announcing that we have already found a new world.
Sometimes the most useful clue is not a spectacular surprise, but a measurement so difficult that it helps rule out where it is not worth looking next.