After the discovery of a Higgs boson by the experiments ATLAS and CMS at the Large Hadron Collider (LHC) at CERN (Geneva, Switzerland) in 2012 and the ensuing Nobel prize for the “fathers” of the Higgs-Englert-Brout mechanism for mass generation in elementary particles, the focus of the global particle physics community has turned to studying this new particle – the mathematical “cornerstone” of the Standard Model (SM) of particle physics – in great detail. ATLAS and CMS have since been measuring the properties of the particle as precisely as possible (mass, couplings, spin, etc.), for two reasons: First, in order to find out whether the new particle is really the one Higgs boson predicted by the SM or “something” else, and second in order use the particle as a tool for discovering “new physics” – i.e. phenomena that are NOT contained in the SM.
As it turns out, the LHC experiments are strongly limited in achieving these purposes, for reasons of low collider energy and insufficient statistics. Therefore, the highest priority of the global particle physics community is to build, as the next international project, a “Higgs factory” – i.e. an electron-positron collider with a centre-of-mass energy of at least 250 GeV and very high luminosity (i.e. number of collisions) capable of producing abundant amounts of Higgs bosons for their high-precision scrutiny.
Several concepts for such a Higgs factory are currently being studied (with names such as ILC, CLIC, LCF, CEPC, FCC, etc.), and a decision is expected by the outcome of the update process of the European strategy for particle physics, expected to conclude in summer 2026 with the adaption of a new European strategy by CERN Council. All of these concepts require significant R&D efforts, with important contributions from partners all over the globe, in particular Europe, USA (also Canada), Japan, and also China.
The Higgs factory studies currently being performed in Europe, USA, Japan, and China are technology-and implementation-specific and organised as collaborative projects. In contrast to this, EAJADE takes the approach of promoting the common use of international beam and test facilities for addressing problems that are common among at least some of the existing Higgs factory proposals. Not only does this make more efficient use of the available resources, but it also increases the exchange between the international collaborations studying FCC-ee, ILC, CLIC and, to a limited extent, CEPC. A similar approach is being implemented for physics and detector studies for future Higgs factories in the framework of the European Committee for Future Accelerators (ECFA).
The key technical challenges for future Higgs factories are many, and the most important ones are addressed in EAJADE, all with important training, skill development and knowledge exchange elements, with the aims of not only performing the necessary R&D steps, but also of global networking, of education of the next generation of researchers, and of knowledge transfer between world regions and institutions: i) Luminosity performance – addressed in existing collider facilities and smaller beam test facilities; ii) upgrades to higher energies and accelerating gradients (covering mostly RF developments and plasma acceleration studies); iii) power efficiency and sustainability aspects; iv) best practices, international collaboration, exchange of ideas and collaborative studies across Higgs factory proposals, training related to prototyping and tests in facilities and laboratory setup.
The contributions to Higgs factory studies provided by EAJADE-seconded researchers are considered essential for many R&D steps, and are highly recognised throughout the community.
