“Researchers at CERN’s LHCb experiment observed B-meson decays that disagree with Standard Model predictions, with analysis of approximately 650 billion decays showing a tension of around 4 sigma. The result, based on 650 billion decays, shows a four-sigma tension with Standard Model predictions and strengthens hints of new physics. William Barter, a particle physicist at the University of Edinburgh, noted a one in 16,000 chance of random fluctuation, while the Compact Muon Solenoid experiment tentatively corroborated the discrepancy despite potential interference from ‘charming penguins.’
“Among the detectors, LHCb has been operating since 1994. Between 2011 and 2018, the experiment recorded 650 billion B meson decays, from which scientists extracted the rare penguin-type events. The analysis focused on an electroweak process where a B meson transforms into a kaon, pion, and two muons – a decay that occurs only once per million B mesons. By precisely measuring the angles and energies of the produced particles, the team found a clear disagreement with the predictions of the Standard Model. The deviation from the Standard Model reaches four standard deviations. In practice, there is only a 1 in 16,000 chance that this result is due to random chance if the Standard Model is correct. The results, published in Physical Review Letters, are consistent with those independently obtained by another LHC experiment, CMS.”
“Physicists think that this B-meson decay — known as a penguin decay — should be particularly sensitive to as-yet undiscovered physics. (British theorist John Ellis coined the term in 1977, owing to the resemblance of a diagram of the decay to a penguin, after losing a bet which forced him to include the word in his next paper). The decay involves a quantum loop, in which a bottom quark changes into a strange quark, through a temporary transition into ‘virtual’ particles that pop in and out of existence. The Standard Model, which cannot explain dark matter, has dominated particle physics for 50 years; ‘penguin’ decays—coined by British theorist John Ellis—involve quantum loops where bottom quarks transform into strange quarks, serving as sensitive probes. If the signal is real, Ben Allanach, a theoretical physicist at the University of Cambridge, suggested a ‘Z prime’ particle could mediate a new force, or ‘leptoquarks’ might explain the observed decay angles.”
“Scientists expect further clarity as they analyze data collected since 2018, with results anticipated next year and future LHC upgrades planned for the 2030s aiming to accrue a dataset 15 times larger. The LHCb collaboration has already begun analyzing new data collected since 2018. This set contains three times more B meson decays than the previous sample, offering a powerful tool to verify the anomaly. Initial analyses are underway, and results are expected in the next few years. In parallel, physicists are refining theoretical calculations to better understand the contribution of charming penguins. If the discrepancy persists or increases, it will strengthen the hypothesis of physics beyond the Standard Model.”
“The Standard Model is built on two of the 20th century’s most transformative advances in physics; quantum mechanics and Einstein’s special relativity. Physicists can compare measurements made at facilities such as the LHC with predictions based on the Standard Model to rigorously test the theory. Despite the fact that we know the Standard Model is incomplete, in over 50 years of increasingly rigorous testing, particle physicists are yet to find a crack in the theory. That is, potentially, until now. Our measurement, accepted for publication in Physical Review Letters, shows a tension of four standard deviations from the expectations of the Standard Model. In real world terms, this means that, after considering the uncertainties from the experimental results and from the theory predictions, there is only a one in 16,000 chance that a random fluctuation in the data this extreme would occur if the Standard Model is correct. Although this falls short of science’s gold standard – what’s known as five sigma, or five standard deviations (about a one in 1.7 million chance) – the evidence is starting to mount.”
“Adding to this compelling narrative are results from an independent LHC experiment, CMS, that were published earlier in 2025. The LHC is a giant particle accelerator built in a 27km-long circular tunnel under the French-Swiss border. Its main purpose is to find cracks in the Standard Model. This theory is our best understanding of fundamental particles and forces, but we know it cannot be the whole story. It does not explain gravity or dark matter – the invisible, so far unmeasured type of matter that makes up approximately 25% of the universe. In the LHC, beams of proton particles traveling in opposite directions are made to collide, in a bid to uncover hints of undiscovered physics. The new results come from LHCb, an experiment at the Large Hadron Collider where these collisions are analyzed. The result comes from studying the decay – a kind of transformation – of sub-atomic particles called B mesons. We investigated how these B mesons decay into other particles, finding that the particular way in which this happens disagrees with the predictions of the Standard Model.”
“Several theoretical models could explain the anomaly. One popular idea involves leptoquarks, hypothetical particles that bridge leptons and quarks – the two families of matter. Another possibility is the existence of more massive versions of known particles. The new data already constrain these models and will guide future research. The LHC detectors, the size of buildings, record collisions that recreate conditions from the beginning of the universe. Why physicists spend decades looking for a crack It may sound strange to outsiders, but the dream of many physicists is precisely to prove that their own theory is incomplete. Not out of whim, but because the Standard Model, as powerful as it is, leaves huge questions unanswered. It doesn’t explain the dark matter that dominates the universe, it doesn’t account for gravity, and it doesn’t clarify why there is more matter than antimatter. Each of these gaps screams that something is missing. That’s why a deviation like this, even small, mobilizes so many people. It could be the first thread of a string that, carefully pulled, leads to new physics capable of filling these gaps.”
“At the world’s largest particle accelerator, CERN physicists observed a particle behaving in a way that theory did not predict, the strongest indication so far of physics beyond what is currently known. There are discoveries that seem small and shake the entire foundation of science. That’s more or less what happened at CERN, the gigantic laboratory where the Large Hadron Collider is located. Studying a very rare type of particle transformation, researchers noticed behavior that simply doesn’t match what the most successful theory in physics predicts, and this has put the scientific community on alert. The theory in question is the so-called Standard Model, the set of rules that describes the fundamental particles and the forces that govern the universe. It is so precise that it predicts results with astonishing accuracy, and for decades it has withstood every test. Precisely because of this, any crack in this wall is worth gold, because it could be the gateway to a new, still unknown physics.”
“An unexpected behavior in a particle decay seems to disagree with the predictions of the Standard Model, despite its high reliability.
