Scientists at the European Organization for Nuclear Research (CERN) Large Hadron Collider (LHC) have observed particle behavior that does not align with the Standard Model of particle physics. This finding emerged from studying rare particle transformations known as "penguin decays." The observed behavior suggests the influence of unknown particles or forces.
The Standard Model describes the fundamental particles and forces of the universe. It has been the dominant theory in particle physics for 50 years. The LHC is designed to find inconsistencies within this model. The new results come from the LHCb experiment, which analyzes proton collisions within the accelerator.
Researchers investigated the decay of subatomic particles called B mesons. They found that the specific manner of these decays disagrees with the Standard Model's predictions. The measurement shows a tension of four standard deviations from expected values. This means there is a one in 16,000 chance that such an extreme fluctuation would occur if the Standard Model were entirely correct.
An independent LHC experiment, CMS, published corroborating results in 2025. While less precise, the CMS findings support the LHCb observations. These "electroweak penguin decays" involve a beauty quark transforming into a strange quark. This process is exceptionally rare, occurring in only one out of a million B mesons.
The scientists carefully analyzed the angles and energies of the particles produced during these decays. Their measurements of these quantities differed from Standard Model predictions. These rare processes are sensitive to the effects of potentially heavy new particles not directly creatable at the LHC. Such indirect observation has historical precedent, as radioactivity was discovered decades before the W bosons responsible for it were directly observed.
Open theoretical questions remain, including the precise contribution of "charming penguins" processes. However, new data already collected will help confirm the situation in the coming years. The LHCb experiment has recorded three times more B mesons since the current study concluded. Future upgrades to the LHC in the 2030s aim to increase the dataset fifteenfold, potentially leading to definitive conclusions about new physics.
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