CERN's LHCb experiment reports first evidence of ultra-rare beauty-particle decay
Physicists at CERN have observed evidence of a decay that occurs once in about 10 billion beauty particles, offering a new test of the Standard Model and a window onto the so-called Zeptoverse.
Physicists working on the Large Hadron Collider beauty (LHCb) experiment at CERN have announced the first evidence of an extremely rare particle decay that had eluded detection for more than four decades. The decay, denoted as B(d) → μ(\mu), involves a particle containing a beauty quark and a down antiquark transforming into two muons and is expected to happen only once in roughly 10 billion beauty-particle decays.
The result, based on data collected in 2024 and 2025 combined with earlier runs from 2011 to 2018, reached a statistical significance of 3.2 sigma, marking the initial evidence of this process from a single experiment. The upgraded LHCb detector, capable of recording collisions at up to five times its previous rate, along with improved particle-identification and machine-learning methods, enabled researchers to isolate the rare signal from background events.
"The measurement is consistent with Standard Model predictions, but it opens a new avenue to probe the Zeptoverse – a regime at distances of about 10⁻²¹ metres where unknown particles and forces may exist," said a spokesperson for the LHCb collaboration.
While the observation does not yet constitute a discovery, which typically requires a five-sigma significance, it provides a valuable test of the leading theory of fundamental particles. The collaboration plans to gather additional data through the early 2030s and anticipates a further detector upgrade that could increase data-collection rates by another factor of ten, enhancing the search for rare decays and potential signs of new physics.