The Higgs field – an invisible quantum field that permeates the entire Universe – gives masses to fundamental particles. The discovery of the Higgs boson confirmed its existence and kick-started the effort to measure its potential energy. The shape of the Higgs potential provides crucial information about the long-term stability of the Universe and depends on the strength of the Higgs “self-coupling” (where multiple Higgs bosons interact).
While the ATLAS Collaboration has previously studied pairs of Higgs bosons (di-Higgs production), research into three Higgs bosons (tri-Higgs production) offers unique opportunities to explore the Higgs self-coupling. In particular, it allows researchers to study the as-yet-unexplored quartic Higgs self-coupling (λ4), which governs the interaction of four Higgs bosons. Additionally, they can test Beyond the Standard Model (BSM) theories which predict tri-Higgs production at higher rates through the decay of new, heavy bosons.
At last week’s Higgs2024 conference, the ATLAS Collaboration unveiled the first LHC search for tri-Higgs production – a process over 60,000 times rarer than the production of a single Higgs boson. Due to its extremely short lifetime, the Higgs boson cannot be directly detected. Instead, physicists look for its decay products, most commonly pairs of bottom quarks. Each bottom quark produces a shower of particles that can be readily detected and reconstructed as a “b-jet”.
Source: ATLAS collaboration (read the entire physics briefing)
Nikhef’s contribution
The researchers from the Nikhef ATLAS group that were involved in the work are Tristan du Pree (staff researcher), Carlo Pandini (postdoc) and Osama Karkout (PhD student). Furthermore, the event generation and simulation of the elusive signal included the work of two UvA MSc students. Tristan du Pree: “This is the very first search for the HHH process and the first ever direct constraint on the Higgs boson’s quartic self-coupling. We are proud to have contributed to this pioneering ATLAS result and we’re pleased that this includes over two years of successful research by our group’s undergraduate students. Although this rare process is still too small to observe at the LHC, this novel probe opens the way for new theoretical interpretations of the Higgs potential.”
