![\"Physics,ATLAS\"](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2026\/04\/file.png\"\/)
<\/a>Figure 1: Representative Feynman diagrams for vector-boson scattering with quartic-gauge boson vertices (left) and tri-boson production with quartic-gauge vertices (right). The aQGCs act on those diagrams through anomalous values or vertices forbidden in the Standard Model. (Image: ATLAS Collaboration\/CERN)<\/p>\nThe self-interactions of W and Z bosons \u2013 the carriers of the weak force \u2013 are tightly constrained in the Standard Model, making them uniquely sensitive to deviations from Standard Model predictions at high energies. By studying rare LHC processes such as vector boson scattering<\/a> (VBS) \u2013 where two vector bosons (photons, W or Z bosons) scatter off one another \u2013 and tri-boson production<\/a> \u2013 the simultaneous production of three vector bosons \u2013 physicists are able to directly examine these interactions. In particular, they can measure quartic gauge couplings<\/a>, where four bosons interact simultaneously (see Figure 1).<\/p>\n The ATLAS Collaboration has released a new search for anomalous quartic gauge couplings<\/a> (aQGCs) that combines eight separate analyses of VBS and tri-boson production in the full LHC Run-2 dataset (2015\u20132018). The search relies on the \u00c9boli model<\/a>, a framework that classifies all possible aQGCs in terms of 17 parameters. Think of these parameters as different “dials” that could be turned up if new phenomena are present. Researchers were able to harmonise the \u00c9boli model treatment across all eight analyses, leading to consistent and comprehensive coverage of its parameters.<\/p>\n ATLAS reports the first combination of VBS and triboson analyses providing the world’s best constraints on anomalous electroweak boson quartic self-couplings.<\/p>\n The combination is presented as confidence intervals<\/a> on the 17 \u00c9boli model parameters, obtained by varying one or two coefficients at a time while fixing the others to zero (see Figure 2). The combined limits are up to 96% tighter than the best previously published individual constraints, establishing them as the best constraints to date. Additional theoretical constraints, which ensure all parameter values are physically possible (e.g. ensuring no negative values), were compared to these experimental limits (see Figure 3).<\/p>\n This analysis represents the most complete and rigorous experimental study of aQGCs performed to date. It establishes a new benchmark for studies of vector boson self-interactions and will serve as a foundation for future global combinations. Looking ahead, ATLAS researchers will extend the search in analyses of the larger Run-3 dataset and prepare for the High-Luminosity LHC, further increasing sensitivity to possible signs of new physics beyond the Standard Model.<\/p>\n<\/a>Figure 2: Combined constraints on anomalous quartic gauge couplings. The top panel illustrates the contribution of each analysis to the total sensitivity, showing the complementarity of the different analyses. The middle panel shows the expected and observed 68% and 95% confidence level intervals from the combined fit. The bottom panel shows, for each parameter, the maximum energy scale probed by the constraints for two illustrative values of the parameters (blue bars). In this figure, a 1.5 TeV cutoff (unitarization) is applied to the anomalous coupling contributions to ensure the results remain physically consistent with theoretical constraints. (Image: ATLAS Collaboration\/CERN)<\/p>\n