Finding one Higgs boson was hard enough, but physicists at the Large Hadron Collider (LHC) are hunting for something even more elusive: pairs of Higgs bosons. At the recent International Conference on High Energy Physics 2026, the ATLAS and CMS collaborations presented new constraints on the double-Higgs production rate, providing insight into how the Higgs boson interacts with itself.

The discovery of the Higgs boson in 2012 at the LHC marked the beginning of a new era in particle physics. Since then, researchers at the LHC have investigated and measured how the Higgs boson interacts with other particles, an important mechanism by which these particles get their mass.

However, physicists have yet to observe the Higgs boson interact with itself. Understanding this process would not only test the limits of the Standard Model, our current best working theory for particle physics, but also help shed light on whether the vacuum of our universe is stable.

The main challenge in studies of double-Higgs production is that the process is incredibly rare. The exact production rate has yet to be determined, but based on predictions from the Standard Model, researchers expect that for approximately every 1,500 single Higgs bosons produced in LHC collisions, only one pair of Higgs bosons will be produced.

To look for double-Higgs production, the ATLAS and CMS collaborations search for signs of the twin Higgs bosons decaying into other particles. Both collaborations investigated a particular decay channel in which one of the twin Higgs bosons decays into a bottom quark and antiquark, and the other into a tau particle and its antiparticle. This is one of the best ways to study double-Higgs production...