ATLAS and CMS narrow in on twin Higgs production

Collaborations at the Large Hadron Collider, ATLAS and CMS, have refined constraints on the production rate of double-Higgs bosons. Researchers presented their findings at the International Conference on High Energy Physics 2026. The Higgs boson was discovered in 2012 at the LHC, initiating a new era in particle physics. The Higgs boson's interactions with other particles are crucial in determining their mass.

However, observing the Higgs boson interacting with itself remains a challenge. This process, if observed, could test the Standard Model's limits and reveal the stability of the universe's vacuum. The rarity of double-Higgs production makes it difficult to study. Researchers estimate that for around 1500 single Higgs bosons produced in LHC collisions, only one pair will be produced.

To search for double-Higgs production, ATLAS and CMS looked for signs of the two Higgs bosons decaying into other particles, specifically one decaying into a bottom quark and antiquark and the other into a tau particle and its antiparticle. Both collaborations searched for double-Higgs production using data from previous LHC runs.

By incorporating the most recent third run of the LHC and using advanced machine-learning techniques, ATLAS and CMS were able to conduct a more sensitive search for double-Higgs bosons decaying into two bottom quarks and two tau particles. They identified more events consistent with double-Higgs production compared to previous studies, but the signal is not strong enough to confirm the production.

ATLAS saw a 2.6 standard deviation excess above what would be expected without double-Higgs production, hinting at the presence of pairs of Higgs bosons. CMS ruled out double-Higgs production rates exceeding four times the current Standard Model prediction. Both collaborations also set limits on the Higgs self-coupling parameter, which determines the Higgs boson's interaction strength with another Higgs boson.

These results indicate a promising direction for future analyses combining full LHC Run 2 and Run 3 datasets and all decay modes, potentially revealing more about double-Higgs boson production. The High-Luminosity LHC, with its increased collision rate, will provide around six times more data, bringing researchers closer to observing double-Higgs boson production. Additional information about these studies is available on the ATLAS and CMS websites.