One of the central questions in this process is which new particle collider should be built once the Large Hadron Collider (LHC) is decommissioned, which is expected to happen in 2041. Although that may seem far off, such a large and complex project requires a long preparation time.
An important input for this discussion comes from a recent update from the ATLAS and CMS experiments at CERN. This update includes new expectations about how sensitive the experiments are at the end of the HL-LHC to several key physics processes. These expectations differ significantly from earlier estimate— so much so that they are influencing the debate on which new collider should be built.
The coordination of this analysis from the ATLAS side was led by Pamela Ferrari, professor by special appointment at the High Energy Physics (HEF) department of Radboud University. Together with two colleagues from the CMS experiment, she led the development of the document.
Pamela Ferrari explains:
The ATLAS and CMS experiments at the High-Luminosity LHC (HL-LHC) will drive significant advances in our understanding of fundamental physics, with 3 ab⁻¹ of physics-quality data per experiment. This dataset, that is expected to be collected at the end of the HL-LHC phase, will enable precision measurements of rare Higgs decays at accuracies of 3-7%, and the determination of the main Higgs boson couplings with ~1-3% precision.
Additionally, the experiments expect to observe Standard Model di-Higgs production with a precision which will inform models of baryogenesis explaining the matter antimatter asymmetry.
The observation of longitudinally polarized vector boson scattering and its cross section at less than 20% uncertainty will provide an independent test of the electroweak symmetry breaking mechanism.
Searches of resonant decays and measurements of top quark properties, further extend the HL-LHC’s reach. Combining the latter with single Higgs and di-Higgs measurements will set even stronger constraints on baryogenesis models and elucidate the stability of the electroweak vacuum, ensuring that these measurements remain at the forefront of particle physics research for decades to come.
The actual discussions on the strategy, in which these new insights will also be considered, will begin in the week of June 23.