An elementary particle collision never before observed

In the standard model of particle physics, the W⁺, W⁻, and Z are so-called vector bosons that transmit the weak force responsible for nuclear decay. But those bosons can also scatter off each other with a cross section that is sensitive to the many details of the theory. Vector-boson scattering is rare; for example, at the Large Hadron Collider the process happens less often than Higgs boson production. Thus, it had never been used to probe particle theory’s accepted paradigm. But ATLAS team members at the LHC have now spotted 34 candidate WW scattering events. The W bosons are neither the particles crashed together by the LHC (those are protons) nor the outgoing particles detected by ATLAS. Rather, as illustrated in the Feynman diagram, during the collision a W (here a W⁺) is radiated by a quark in each of the protons. After scattering,...