The zeptoverse explained: what CERN's latest result means for your physics class

Expect a hand to go up in your next physics lesson. On 3 November, CERN announced evidence of a decay that happens to just one beauty particle in every ten billion, and the word doing the rounds is "zeptoverse".

Here is what the result shows, and why it is such a good one to teach.

What the scientists found

The result comes from LHCb, one of the four main experiments at the Large Hadron Collider. It studies particles containing beauty quarks, which last about one and a half trillionths of a second before decaying.

The decay is called Bd to mu mu. A meson made of a beauty quark and a down antiquark turns into a muon and an antimuon. Physicists have been looking for it since 1984.

Two things changed the picture. A 2024 upgrade let LHCb collect data at up to five times its previous rate, and machine learning helped the team separate the rare signal from a vast background.

There is a neat link for your class too. The electron was discovered in 1897 at Cambridge's Cavendish Laboratory. Almost 130 years later, Dr Harry Cliff of the same laboratory co-led this analysis.

So what is the zeptoverse?

It is a nickname, not a place. A zeptometre is a trillionth of a billionth of a metre, and "zeptoverse" is shorthand for physics at those distances. For scale, a proton is more than a million zeptometres across.

The Large Hadron Collider can probe down to around 100 zeptometres. It has not yet found the new particles that many theories predicted, so they may be hiding at smaller scales, perhaps as small as a single zeptometre.

Particles down there could help explain dark matter, or how matter formed in the Big Bang.

Nobody has seen anything at that scale directly. Instead, rare decays offer a way in: a new particle beyond the LHC's direct reach can still influence how often a decay happens.

It is the same logic as finding an exoplanet from the wobble of its star, because you measure the effect and not the object.

The rarer the decay, the more sensitive it tends to be, which is why this one matters. As Dr Cliff puts it: "We're knocking on the door of the zeptoverse now."

Three things worth picking out with your class

The physics is only half of it. This result is also a clear example of how science works.

• Evidence is not discovery. At 3.2 sigma, the result clears the three sigma needed to claim evidence, but not the five needed for a discovery. It has not been peer reviewed yet, and a similar claim in 2015 was not confirmed by later analyses.
• Agreeing with the theory still counts. The measurements fit the Standard Model, so this is not new physics. It still narrows things down, because any new theory now has to fit this result too.
• The science carries on with the machine switched off. The LHC has been in Long Shutdown 3 since 29 June, but this result uses data from 2024 and 2025, combined with data from 2011 to 2018. Physicists are still working through what LHCb recorded.

Where the story goes next

The next target is five sigma, which would make this the rarest decay of a beauty particle observed to date. The High-Luminosity LHC is due to start up in 2030, and a further LHCb upgrade planned for the mid-2030s could increase the rate of data collection tenfold.

By the time your current Year 12s finish a physics degree, the High-Luminosity LHC should be running. Some of them could end up working on its data.

From the classroom to CERN

A story like this sticks better when your students can put their questions to people from CERN's scientific community. CERN does its best to tailor group tours to your areas of interest, so tell them what your class has been reading about.

Sixth formers have a link of their own. The muon was discovered using a cloud chamber. At CERN's Science Gateway, the Cloud Chamber workshop has 16 to 19 year olds building one, subject to availability.

We have taken over 10,000 students to CERN and we are the UK's leading CERN school trips provider, so we know how the days fit together. If your group's questions are heading that way, see the suggested itinerary on our CERN school trips page.