More than 150 German particle physicists gathered at Bonn University for a community event on a future collider at CERN. More precisely, the focus set for this meeting was to discuss the opportunities that the FCC-ee would offer should this collider be built at CERN. The event was organised by the German committee for particle physics, KET, and took place from 22 to 24 May. Representatives from almost all German institutes and groups active in particle physics were present, an attendance that shows the large interest in the collider to be built at CERN after the successful completion of the HL-LHC programme.
The main workshop was preceded by a dedicated session with more than 80 early-career scientists, organised by the Young High Energy Physicists Association, yHEP, to bring the generation that will benefit most from a future collider at CERN up to speed on the workshop topics. It included a presentation by former ECFA chair Karl Jakobs (Freiburg University) “From Strategy Discussions to Decision-Taking for Large Projects”, explaining the mechanisms and bodies involved in setting a project like the FCC-ee on track.
The opening session of the main workshop featured a fresh view on “The physics case for an e+e– collider at CERN” by Margarete Mühlleitner (KIT Karlsruhe), who spread excitement about the strong and comprehensive physics case from super-precise measurements of the properties of the Z boson, the W boson and the top quark to what most people associate with a future e+e– collider: precision measurements of the Higgs boson and insights about its connection to many of the still open questions of particle physics like dark matter or the matter–antimatter asymmetry. Markus Klute (KIT Karlsruhe) gave an in-depth review of the FCC-ee project. The midterm results of the FCC feasibility study indicate that no showstoppers were found in all the aspects studied so far and that the integrated FCC programme offers unparalleled exploration potential through precision measurements and direct searches. The picture was rounded off by a presentation from Jenny List (DESY, Hamburg) who talked about alternative options to realise an e+e– Higgs factory at CERN, and the perspective of the early-career researchers was highlighted by Michael Lupberger (Bonn University). While all these presentations concentrated on the science and technology of the FCC-ee or alternatives, Eckart Lilienthal, representing the German Ministry of Education and Research, BMBF, reminded the audience that a future collider project at CERN needs an affordable financial plan and that – given the large uncertainties at present – this requires the community to prepare for different scenarios including one without the FCC-ee. Lilienthal confirmed that the future of CERN remains of the highest priority to BMBF.
The event was an important step in building consensus in the German community for a future collider project at CERN
The workshop went on to review many aspects of the FCC-ee and possible alternatives in more detail: accelerator R&D, detector concepts and technologies, computing and software, theory challenges as well as sustainability. The workshop witnessed the first meetings of the newly established German detector R&D consortia on silicon detectors, gaseous detectors and calorimetry. They will receive BMBF funding for the next three years and will allow German groups to strongly participate in the recently formed international DRD consortia in the context of the ECFA detector roadmap.
The path ahead
The workshop concluded with discussion sessions on the future collider scenarios for CERN, the engagement of the German community and a path to prepare the German input to the update of the European Strategy for Particle Physics. A series of three additional community workshops will be held in Germany before this input is due in March 2025.
The Bonn event was an important step in building consensus in the German community for a future collider project at CERN. The FCC-ee project generated a lot of interest and many groups plan to embark more strongly on this project. Contributions concerning the physics case, theory challenges, detector design and development, software, computing, and accelerator development were discussed. Alternative options for a future collider project at CERN need to be kept open to address the unanswered fundamental questions of particle physics in case the FCC-ee is not built at CERN. This event was clear evidence that a bright future for CERN remains of highest priority for the German particle-physics community and funding agency.
