CERN LHCb Researchers Find Evidence of Rare Particle Decay
After more than four decades of searching, physicists at the Large Hadron Collider Beauty experiment have found evidence of a rare particle decay.
After more than forty years of effort, scientists working with the Large Hadron Collider Beauty experiment have uncovered evidence of an exceedingly rare type of particle decay. In a seminar held on November 3, and detailed in a preprint paper on arXiv, the LHCb Collaboration announced signs of a phenomenon thought to occur only once in ten billion events involving the death of a beauty particle.
The findings offer a powerful new test of the Standard Model and a window into potential new physics, according to Niladri Sahoo, a particle physicist at the University of Birmingham and convener of the LHCb Very Rare Decays working group. The recent update to the LHCb project significantly boosted its particle collision detection rate, allowing researchers to home in on rare physics sought since the 1980s by leveraging machine learning techniques to increase the signal-to-noise ratio.
Detecting the Zeptoverse and Rare Decays
The breakthrough centers on the potential detection of the decay of a particle known as a B d meson into a muon and an anti-muon. The meson comprises a beauty quark and a down antiquark. Researchers produced the fleeting particles by colliding protons at near-light speeds, yielding an ephemeral spray that combines via the strong nuclear force. Only one in every ten billion of these decays results in a muon and an anti-muon.
Claiming evidence for the phenomenon requires a significance level of three standard deviations, or “3 sigma,” corresponding to a 0.3 percent chance that the result is a fluke. Combining data gathered between 2011 and 2018 with newer observations from 2024 and 2025 yielded a significance level of 3.2 sigma. Attaining the gold standard 5-sigma value will require further research and future upgrades planned for the 2030s.
“Seeing clear evidence for this rarest decay for the first time was thrilling,” said Harry Cliff, a particle physicist at the University of Cambridge and leader of the analysis team. “We’re knocking on the door of the zeptoverse now. I can’t wait to see what we find as we explore deeper.”