LHCb finds a hint of an exceptionally rare particle decay
· BehindLines newsroom
A long anticipated particle transformation is emerging in LHCb measurements. On 3 November, the collaboration presented evidence at CERN for the neutral B⁰ meson decaying into a muon and its antiparticle. The result concerns a very rare process predicted by the standard model, the framework describing particles and their interactions.
A signal still awaiting confirmation
CERN reports a statistical significance of 3 standard deviations for the 2024 and 2025 data. Combining them with data from 2011 to 2018 brings the figure to 3.2. This is evidence: the aim remains to reach the threshold of 5 standard deviations used to claim an observation.
The expected rate, around one decay in ten billion, concerns this particular meson channel. It does not mean that any given accelerator collision has that probability of producing the signal. The announced advance is evidence from a single experiment. CERN recalls that earlier evidence from a combined analysis was not confirmed in subsequent updates.
Identifying the right particles
Italy's INFN highlights the role of the system that identifies muons. Some of its detection chambers were built at the Frascati laboratory. Marco Santimaria co-led the analysis there, conducted by an international team of 19 physicists.
Distinguishing these muons from the many signals that resemble them is essential to measuring such an infrequent transformation. Detector improvements and data analysis have made this separation more effective.
The two organisations describe a result compatible with current predictions. For physics, the value lies in narrowing the possibilities left for hypothetical unknown particles: a more precise measurement might reveal a discrepancy. For now, the announcement represents neither the discovery of a new particle nor definitive confirmation of the process being sought.