Scientists close in on mysterious ‘zeptoverse’ after 40-year hunt for ultra-rare particle

Cambridge physicists have found evidence of an event that happens just once in every 10 billion particles, bringing them closer to understanding dark matter, the Big Bang and a mysterious world far smaller than an atom

British scientists have detected signs of an extraordinarily rare event deep inside the building blocks of matter, raising hopes of discovering previously unknown particles that could help explain how the universe began.

The breakthrough, led by physicists at the University of Cambridge, follows more than 40 years of searching and could help researchers explore a mysterious world billions of times smaller than an atom.

Known as the zeptoverse, this unimaginably tiny realm is one of the places scientists hope to find answers to some of the biggest unanswered questions in physics, including what dark matter is made of and why the universe contains so much more matter than antimatter.

The research was carried out at the Large Hadron Collider (LHC), an enormous underground machine at CERN, near Geneva, which smashes particles together at tremendous speeds to investigate what they are made of.

Scientists were studying particles containing what are known as beauty quarks, short-lived building blocks of matter that are produced during the collisions.

These particles survive for only around one-and-a-half trillionths of a second before breaking down into other particles.

The Cambridge-led team has now found evidence of an exceptionally rare event in which one of these particles produces two smaller particles called muons, which are heavier relatives of electrons.

Dr Harry Cliff, from Cambridge’s Cavendish Laboratory, who led the analysis, said: “What we found in these latest results is an incredibly rare decay of one of these beauty particles, where it turns into two even smaller particles called muons.

“This process only happens for one in every ten billion beauty particles, so it’s incredibly difficult to find.”

Researchers have been hunting for evidence of this particular event since 1984, but its extreme rarity has made it almost impossible to detect.

The team finally made progress using a recently upgraded detector at CERN, which collected enormous amounts of information during 2024 and 2025.

With the help of machine learning, scientists were able to sift through the results and separate the faint signals they were looking for from countless other particle collisions.

The finding could eventually help scientists investigate a world so small that its distances are measured in zeptometres – each equivalent to a trillionth of a billionth of a metre.

Researchers believe unknown particles or forces may exist at these scales, potentially offering clues to mysteries that current scientific theories cannot fully explain.

While the latest results do not establish the existence of any new particles, they give scientists a powerful new way to search for signs of previously undiscovered physics.

The evidence has reached a statistical confidence level known as 3.2 sigma, enough to suggest the signal is real, although more data will be required before physicists can declare a confirmed discovery.

“Physicists have been looking for this rare type of decay since 1984, which was before I was born,” Cliff added.

“Seeing clear evidence for this rarest decay for the first time was thrilling,” he added. “We’re knocking on the door of the zeptoverse now. I can’t wait to see what we find as we explore deeper.”

The findings, which have yet to undergo peer review, are being presented at CERN on today.

Scientists hope further upgrades to the collider’s equipment in the 2030s will allow them to examine these rare events in much greater detail.

Professor Tim Gershon, from the University of Warwick, who leads the LHCb experiment, said: “This fantastic result showcases the extraordinary capabilities of LHCb to probe nature at the fundamental level. This project, driven and led by UK physicists, is producing beautiful science.”

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_{Main image: Inside the Large Hadron Collider’s underground tunnel at CERN, near Geneva, where scientists smash particles together at enormous speeds to investigate the building blocks of the universe. A Cambridge-led team has now detected evidence of an exceptionally rare particle decay that could help physicists explore the mysterious ‘zeptoverse’, a realm billions of times smaller than an atom. Credit: Maximilien Brice / CERN / Wikimedia Commons (CC BY-SA 3.0)}