Physicists at CERN’s LHCb experiment have announced the detection of evidence for a rare particle decay process occurring in approximately one of every 10 billion beauty particle decays. The discovery marks the first time a single experiment has gathered sufficient evidence for this decay, which involves a Bd particle decaying into a pair of muons. The results align with predictions from the Standard Model and contribute to the scientific understanding of fundamental particles and their interactions.
Rare particle decays are valuable for physics research because quantum effects allow unobserved particles to influence how they occur. By measuring these extremely uncommon processes with high precision, researchers can identify discrepancies between experimental findings and theoretical predictions, potentially indicating the existence of unknown particles. The specific decay observed belongs to a category physicists have termed “golden channels” for investigating physics that extends beyond the Standard Model.
A related decay involving a different beauty particle, called Bs, was previously confirmed in 2015 through a joint analysis by LHCb and CMS collaborations. However, subsequent analyses using data collected through 2018 could not confirm earlier evidence for the Bd decay. The Bs decay occurs roughly three times per billion beauty particle events, while the Bd process is predicted to occur about 30 times less frequently, explaining the difficulty in its detection.
The breakthrough became possible following significant enhancements to the LHCb detector. Since beginning data collection in 2024, the upgraded experiment has operated at five times the previous rate while improving its ability to identify particle types. Researchers combined these technological improvements with machine learning techniques to distinguish the extremely rare signals from background noise. Using data from 2024 and 2025, along with earlier measurements from 2011 to 2018, the team achieved a statistical significance of 3.2 standard deviations, meeting the threshold for evidence of a new phenomenon.
Although this represents a major achievement, physicists have not yet reached the five standard deviations required to declare a confirmed observation. Planned upgrades to the Large Hadron Collider, including the High Luminosity LHC expected to begin operations in 2030, could increase data collection capacity tenfold, enabling more precise measurements and potentially revealing subtle effects of undiscovered particles.
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