CERN Detects Evidence of Ultra-Rare Particle Decay After 40 Years of Research

The finding comes from the upgraded Large Hadron Collider beauty (LHCb) experiment at CERN's Large Hadron Collider (LHC). Researchers say the result provides a new opportunity to test the Standard Model, the leading theory explaining fundamental particles and the interactions between them.

The Zeptoverse refers to an extremely small scale of nature involving distances as short as a zeptometre, measuring \(10^{-21}\) metres. This is one billionth of a trillionth of a metre. Investigating nature at these incredibly small scales could help scientists explore particles and fundamental forces that have not yet been detected, potentially revealing gaps in the current understanding of the universe.

The LHCb collaboration has found evidence of a rare particle decay known as 'Bd to mu mu'. The process involves a particle containing a beauty quark and a down antiquark decaying into two muons. Muons are heavier relatives of electrons. According to scientists' predictions, this decay occurs only around once in every 10 billion beauty-particle decays.

Researchers have been searching for evidence of this process for more than 40 years. The latest measurement reached a statistical significance of 3.2 sigma, making it the first evidence of this particular decay obtained from a single experiment.

The upgraded LHCb detector played an important role in the finding. It can record particle collisions at up to five times its previous rate, allowing researchers to examine significantly more collision data. The collaboration combined observations collected during 2024 and 2025 with earlier data gathered between 2011 and 2018.

Improved particle-identification capabilities and machine-learning techniques helped researchers distinguish the extremely rare decay signal from background events generated during particle collisions. These advances enabled scientists to identify evidence of a process that had remained elusive despite decades of research.

What is the zeptoverse, and what could it tell us about dark matter? ⚛️ A Cambridge-led team of physicists, working at @CERN, have detected an ultra-rare decay of a subatomic particle known as a beauty quark. The results are at such tiny scales – trillionths of a billionth of a metre – that they could open the door to the zeptoverse, where new physics and subatomic particles could be hiding. Find out more 👉 https://t.co/h9MPldzZaZ

— Cambridge University (@Cambridge_Uni) November 3, 2026

However, the finding does not mean that scientists have discovered new physics. The measurement remains consistent with predictions made by the Standard Model. In particle physics, a statistical significance of five sigma is generally required before a result can be declared a discovery.

Researchers plan to continue collecting data into the early 2030s. A further upgrade could increase the experiment's data collection rate by another factor of 10, giving scientists greater opportunities to investigate rare particle decays and search for evidence of previously unknown particles.

The latest result marks an important development in the long-running search for extremely rare particle interactions. Although it does not yet establish the existence of physics beyond the Standard Model, continued observations could help researchers investigate the Zeptoverse and examine whether previously undetected particles or fundamental forces exist at the smallest scales of nature.