Physicists at CERN have obtained the first evidence of an incredibly rare particle decay, advancing the exploration of the "zeptoverse"—a physical scale measuring distances in zeptometers. Using the upgraded Large Hadron Collider beauty (LHCb) experiment, researchers identified a neutral B meson decaying into a muon and an antimuon, a phenomenon predicted to occur only once in every 10 billion decays, WIRED reported.
LHCb Detectors Capture One-in-Ten-Billion Decay Events
The discovery centers on the decay of a “beauty” particle, a subatomic particle smaller than an atom that exists for only one and a half trillionths of a second before transforming. According to the Science and Technology Facilities Council (STFC), the LHCb team identified the “Bd to mu” decay, where a beauty particle breaks down into two muons—particles that are essentially heavier versions of electrons. While the result reached a statistical significance of 3.2 sigma, STFC noted it remains below the five-sigma threshold required to officially claim a formal discovery in particle physics.
This specific decay has been a target for researchers for over four decades. To isolate these rare signals, the team had to distinguish them from a massive amount of background noise generated during proton collisions. The precision required to pick these specific muons out of the “overwhelming background” was a primary hurdle for the international analysis team, according to CERN.
The data used for this analysis was not limited to recent runs. The research team combined new data collected throughout 2024 and 2025 with datasets from earlier experimental runs conducted between 2011 and 2018, as reported by STFC.
Upgraded Hardware and Machine Learning Drive Zeptoverse Access
The ability to observe such an improbable event was made possible by significant technical upgrades to the Large Hadron Collider in 2024. These enhancements directly addressed the data bottleneck that previously hindered the observation of rare beauty-particle decays.
- Increased Throughput: The upgraded LHCb detector can now record particle collisions at up to five times its previous rate, providing a significantly larger sample size for study, according to STFC.
- Signal Processing: Researchers utilized new machine-learning techniques to suppress the vast background of other processes that would otherwise have swamped the rare signals, according to CERN.
- Enhanced Identification: Improved particle identification capabilities allowed for more precise measurements of various decay types, including the “Bs to mu” decay first observed in 2015.
This leap in data collection and processing speed is what allows scientists to peer into the zeptoverse. A zeptometer is equivalent to one quadrillionth of a meter. To visualize this scale, an atom is approximately 100,000 million zeptometers in diameter—a ratio comparable to the size difference between a human being and one of their own skin cells, WIRED reported.
The Search for Dark Matter and New Physics
While the current results align with the predictions of the Standard Model—the fundamental framework of particle physics—the implications of the zeptoverse extend beyond mere confirmation. Scientists are looking for “cracks” in this model that might indicate the existence of undiscovered particles or forces.
Dr Harry Cliff of Cambridge University told BBC News that this subatomic interaction provides a “ringside seat” to the behavior of potential new particles. The scale of the zeptoverse is particularly interesting because some theories suggest that particles become more sensitive to dark matter at these extreme distances. Because dark matter is invisible and only detectable through its gravitational influence on normal matter, observing how quarks interact and break down at these scales could provide the clues needed to identify it, according to BBC News.
The research, which is detailed in a preprint on arXiv, suggests that the zeptoverse may act as a gateway to understanding the earliest moments of the universe. If physicists can probe even deeper, they might eventually reach the Planck length—a scale 60 trillion times smaller than a zeptometer. At that level, current laws of physics are expected to break down entirely, potentially offering insight into the infinitesimal fraction of a second following the Big Bang.
For now, the focus remains on increasing the volume of data. As Dr Cliff told BBC News, the next step is to go in and explore the particles waiting in that micro-world, which requires more data to reach the gold-standard five-sigma level of certainty.
