After a search spanning more than four decades, physicists at the European Organization for Nuclear Research (CERN) have captured evidence of a subatomic particle decay predicted to occur just once in every 10 billion events, according to findings detailed by Moneycontrol.
The detection centers on a short-lived beauty particle transformation. This is known as Bd to mu, or Bd meson decay. A particle containing a beauty quark and a down antiquark decays into a muon and an antiparticle.
A related process involving the heavier Bs meson was confirmed in 2015 by the LHCb and CMS collaborations. The Bd decay proves roughly 30 times rarer. It has a theoretically predicted probability of about 1.03 per 10 billion according to DongA Science.
CERN Captures Rare Particle Decay
The breakthrough was achieved using the upgraded Large Hadron Collider beauty detector at CERN’s Large Hadron Collider, located near Geneva, Switzerland. An upgrade in 2022 boosted its data collection capacity fivefold per second. The experiment analyzed proton collisions gathered across 2024 and 2025.
Researchers deployed machine learning to sift through dense collision signals. Analyzing only the recent observation data yielded evidence at a statistical significance of 3 sigma. Combining this with legacy data gathered between 2011 and 2018 pushed the overall statistical significance to 3.2 sigma. This crossed the threshold required to claim evidence of a phenomenon.
Physicists Probe the Zeptoverse
Investigating these events opens a window into the zeptoverse. This is a subatomic frontier measured at distances as small as a zeptometre, or one billionth of a trillionth of a metre. Exploring nature at this scale may help physicists investigate undiscovered particles. It may test the limits of the Standard Model.
This work may potentially address cosmological questions regarding dark matter and dark energy. They together account for approximately 95% of the universe, as noted by Yahoo News Australia.
High-Luminosity Collider Aims for 5 Sigma
The 3.2-sigma result marks strong evidence. Particle physics generally demands a 5-sigma threshold to officially claim a formal discovery. CERN plans further expansion through the operation of the High-Luminosity Large Hadron Collider around 2030.
“Seeing evidence of this rare decay is incredibly exciting, opening up new possibilities to probe beyond the direct reach of the LHC,” explained Harry Cliff, LHCb's Rare Decays Convener and Analysis Co-lead.
Subsequent upgrades to the LHCb detector are slated for the mid-2030s. These enhancements aim to increase data collection rates by another factor of 10. They will enable researchers to search for subtle deviations that might signal unknown physical laws.
Earlier coverage: CERN Researchers Find Evidence of Rare Beauty Particle Decay
