CERN experiments find persistent cracks in particle physics’ Standard Model

A decade-old crack in particle physics' most successful theory refuses to close. The LHCb collaboration at CERN has published its most comprehensive analysis of a rare B-meson decay, finding that measured particle trajectories still deviate from Standard Model predictions at a level of roughly four standard deviations — a one-in-16,000 chance of being a statistical fluke. Separately, the ATLAS and CMS experiments have reported new hints of twin Higgs boson production, with ATLAS observing a 2.6-standard-deviation excess above background expectations.phys+3

A Persistent Tension

The LHCb result, published in Physical Review Letters, draws on proton-proton collision data collected between 2011 and 2018 — a sample encompassing roughly 650 billion B-meson decays. The decay under study, in which a neutral B meson transforms into an excited kaon and a muon-antimuon pair, occurs only about once per million B-meson decays. After reconstruction and selection, approximately 17,000 signal events formed the basis of the analysis.spacedaily

An observable called P₅′, constructed from the angles of the final-state particles, continues to disagree with theoretical predictions in the same energy region where tension first appeared in 2013. According to CERN, "the new measurements show the same pattern of tensions with the Standard Model that we have seen before". The collaboration also found discrepancies in the differential branching fraction and forward-backward asymmetry, all leaning in a common direction.home+1

William Barter, a particle physicist at the University of Edinburgh who works on LHCb, told Nature that the chance of random noise producing this signal under the Standard Model is around one in 16,000.nature

Twin Higgs Hints at ICHEP 2026

At the International Conference on High Energy Physics 2026, ATLAS and CMS presented new constraints on double-Higgs production — a process expected to occur only once for every 1,500 single Higgs bosons produced. Using combined Run 2 and Run 3 data with machine-learning techniques, the ATLAS collaboration measured the double-Higgs production rate at 2.6 ± 1.4 times the Standard Model prediction. CMS ruled out production rates larger than four times the Standard Model expectation.miragenews+2

Both collaborations set new limits on the Higgs self-coupling parameter, which governs how strongly the Higgs boson interacts with itself — a measurement that could reveal whether the vacuum of our universe is stable.phys

Discovery Remains Elusive

Neither result crosses the five-sigma threshold required to claim a discovery. The B-meson anomaly faces a stubborn alternative explanation: poorly understood strong-interaction effects from charm quarks — so-called "charming penguins" — could mimic new physics. LHCb's larger Run 3 dataset, containing roughly three times more B-meson decays, is already under analysis.techno-science+1

For double-Higgs production, the High-Luminosity LHC upgrade promises six times more data, which could finally bring the process into view. Until then, particle physics remains in a frustrating middle ground — too many hints to ignore, too few to declare anything found.phys