A particle decay that researchers have sought for more than four decades may have left its first statistical trace. The LHCb Collaboration announced evidence for the exceptionally rare process at a November 3 seminar, according to a ScienceAlert report by Ivan Farkas. The result is intriguing, but it is not yet a confirmed discovery: the analysis was described in a preprint that had not been peer-reviewed.
The decay involves a B_d meson, a short-lived particle made of a beauty quark and a down antiquark. The proposed outcome is a muon and an antimuon. According to the report, this decay is expected only about once in every ten billion decays of the relevant beauty particles, making it exceptionally difficult to pick out amid other particle events.
LHCb looked for the signal in data from 2024 and 2025, combined with earlier data collected between 2011 and 2018. The report says a recent upgrade increased the experiment’s ability to detect particle collisions, while machine-learning techniques helped separate potential signals from background. The particles themselves are fleeting: the account describes the B_d mesons decaying in about one and a half trillionths of a second.
The combined result reached a statistical significance of 3.2 sigma. In the report’s framing, that is enough to present evidence, but it falls short of the five-sigma level commonly treated as the gold standard for claiming a discovery. More data and analysis are needed to establish whether the decay has been observed. The distinction matters: evidence at this level can point researchers toward a rare process, while still leaving room for a statistical fluctuation.
The result also offers a test of the Standard Model, the framework that describes many known particles and their interactions. The report says the findings are consistent with its expectations and constrain possible contributions from new physics at energy scales beyond those accessible through direct production at the Large Hadron Collider. That makes the decay scientifically useful even without a discovery claim: an unusually rare process gives physicists another way to check how well the model describes nature.
The broader possibility is that new physics could be revealed indirectly through the rates of particle decays, rather than by producing a new particle directly. The report presents that as a prospect, not a finding from this result. It also notes that the Standard Model leaves major cosmic questions unresolved, including the nature of dark matter and the imbalance between matter and antimatter. The current measurement does not answer those questions.
The LHCb team will need further evidence to determine whether the signal grows to discovery-level significance. The report points to planned upgrades in the 2030s that are expected to increase the number of collisions and data collection rate. For now, the finding is a promising, qualified step in the search for a decay so rare that it takes enormous datasets to test whether it occurs as predicted.
<a href="https://www.sciencealert.com/after-42-years-of-searching-physicists-find-evidence-of-a-one-in-10-billion-particle-decay">Source: ScienceAlert report</a>