A Cambridge-led team of physicists has found evidence for the rarest decay of a subatomic beauty particle ever seen, using the upgraded LHCb experiment at CERN near Geneva. The result is the first time a single experiment has reported evidence for this decay, and it may help physicists probe the ultra-small distances they call the zeptoverse.
Key facts
- The study was done at the upgraded LHCb experiment at CERN’s Large Hadron Collider near Geneva.
- The team says it found evidence for the decay B0 → μ+μ−, an exceptionally rare beauty-particle process.
- Combining 2024 and 2025 data with earlier data lifted the signal to 3.2 sigma.
- The results were announced on 3 November and have not yet been peer-reviewed.
- The new measurement agrees with the Standard Model of particle physics.
Why this matters for particle physics research
The finding gives physicists a sharper way to test whether unknown particles are influencing the way beauty quarks decay. Because the process is so rare, even small deviations could point to physics beyond the Standard Model. For researchers, the immediate value is not a new particle discovery, but a more precise constraint on where to look next.
The result also highlights why the LHCb upgrade matters. The collaboration used improved particle-identification performance and machine-learning tools to reduce background noise in the 2024 and 2025 data. A further upgrade planned for the middle of the 2030s is expected to increase data collection by another order of magnitude, which could turn these decays into even more precise probes.
- Who is affected: particle physicists working on rare-decay searches and Standard Model tests.
- Where: CERN’s Large Hadron Collider near Geneva, through the LHCb experiment.
- What comes next: more data and a planned 2030s upgrade to improve sensitivity.
What did the team actually find?
The researchers report evidence for the decay known as B0 → μ+μ−, where a beauty particle turns into two muons. According to the team, the process happens only about once in every ten billion beauty particles, which is why it has been so hard to observe.
The analysis combined new data from 2024 and 2025 with earlier data collected between 2011 and 2018. That larger sample pushed the signal above the three-sigma level, a standard threshold for evidence of a new phenomenon.
How does this fit with the Standard Model?
The new results agree with the Standard Model, which is important because rare decays can expose tiny effects from particles that are not directly visible in the detector. In this case, the agreement narrows the space for new physics rather than overturning the current theory.
That still matters to the field. Physicists treat these rare channels as “golden channels” because they can reveal subtle quantum influences from particles far beyond the detector’s direct reach. The present measurement adds a stronger benchmark for future searches.
Why are physicists talking about the zeptoverse?
The term refers to distances even smaller than those the LHC can directly resolve, down to about a zeptometre, or a trillionth of a billionth of a metre. The collaboration says the collider is already probing scales around a hundred zeptometres, and the absence of new particles there suggests they may be hiding at even shorter distances.
That is why this decay matters: by measuring how often it happens, physicists can infer whether unseen particles are nudging the process along. The work does not claim a discovery of new physics, but it strengthens the experimental route toward finding it.
Frequently asked questions
What is B0 → μ+μ−?
It is an extremely rare decay in which a beauty particle turns into two muons. The Cambridge-led team says this process occurs only once in roughly ten billion beauty particles, which is why evidence for it has taken so long to appear.
Does this mean scientists found new physics?
No. The result agrees with the Standard Model. What it does is tighten the search for new particles by improving the measurement of a decay that is highly sensitive to tiny influences beyond the known theory.
