Deep beneath the French-Swiss border, scientists at CERN have been smashing protons together for over a decade. Most results match what physicists expected, but one rare decay has started to behave strangely. The LHCb experiment discovered that beauty mesons decay in a way the Standard Model, the rulebook of physics for fifty years, cannot fully explain.
The difference is small but persistent. LHCb found a tension of four standard deviations between what they measured and what the theory predicts. This means there is roughly a one-in-16,000 chance this difference happened by accident. However, physicists need five standard deviations to claim a real discovery.
The decay involves a beauty quark transforming into a strange quark through a quantum loop. Unknown particles could hide inside this loop and change the measurements. LHCb studied 650 billion B-meson decays from 2011 to 2018, and found the numbers do not match predictions.
CMS, another detector at CERN, published similar results in 2025. Although less precise, both experiments point in the same direction. With three times more data already collected since 2018, and upgrades planned for the 2030s, scientists could confirm this discovery within one or two years. If confirmed, this could reveal a completely new understanding of physics beyond the Standard Model.