The European Strategy for Particle Physics is the cornerstone of Europe’s decision-making process for the long-term future of the field. Mandated by the CERN Council, it is formed through a broad consultation of the grass-roots particle physics community, it actively solicits the opinions of physicists from around the world, and it is developed in close coordination with similar processes in the US and Japan in order to ensure coordination between regions and optimal use of resources globally.
The European Strategy process was initiated by the CERN Council in 2005, resulting in a document being adopted by the Council in 2006. Unsurprisingly, this document placed the LHC at the top of European particle physics’ scientific priorities, with a significant luminosity upgrade already being mooted. A ramp-up of R&D into future accelerators also featured high on the priority list, followed by coordination with a potential International Linear Collider, and participation in a global neutrino programme. The original Strategy also foresaw increased collaboration with neighbouring fields such as astroparticle and nuclear physics, and it recognised the importance of complementary issues such as communications and technology transfer.
The original European Strategy prescribed regular updates to take into account the evolution of the field. The first of these was prepared in 2012 and adopted in 2013. By this time, the LHC had proved its capacity with the discovery of the long-sought Higgs boson, evidence for the Brout-Englert-Higgs mechanism through which fundamental particles acquire their mass.
Again, it came as no surprise that the LHC topped the list of scientific priorities for European particle physics, with the high-luminosity upgrade increasing in importance, and preparations for the post-LHC future taking shape. “Europe”, said the Strategy document, “needs to be in a position to propose an ambitious post-LHC accelerator project at CERN by the time of the next Strategy update.”
The remainder of the updated recommendations represented logical and evidence-based evolutions of those contained in the initial European Strategy. All have been, or are in the process of being, implemented.
Setting the stage
As the second update of the European Strategy got underway, in 2016, the stakes were high. Europe, in collaboration with partners from around the world, was engaged in R&D projects for a range of ambitious post-LHC facilities at CERN under the CLIC and FCC umbrellas. It was time to check progress on these, matching their expected performance to physics needs as well as compared to other projects being considered beyond Europe: the International Linear Collider (ILC) project in Japan, and the Circular Electron-Positron Collider (CEPC) in China. Discussions would be based on scientific evidence gleaned from the impressive results coming in from the LHC, as well as from technological and resourcing considerations.
In other areas of particle physics, much had changed since the last strategy update. Europe, through CERN, was contributing fully to a globally-coordinated neutrino programme with experiments to be carried out in the USA and Japan. The ILC, which would be complementary to the LHC, remained on the table with a site having been identified in Japan and a decision on whether to go forward eagerly anticipated. There were ambitious plans to build a large collider in China. And at CERN, a study to investigate the potential for physics beyond colliders, maximising the potential for CERN’s unique accelerator complex, was launched in 2016. All of these factors have fed into the updated European Strategy for Particle Physics.
The current update of the European Strategy for Particle Physics formally got under way in September 2018, when the CERN Council, comprising representatives from CERN’s Member and Associate Member States, established a European Strategy Group (ESG) to coordinate the process. The ESG worked in close consultation with the scientific community: a call for input from the entire physics community was made in March 2018 which received nearly two hundred submissions. These were discussed during an Open Symposium in Granada in May 2019 and distilled into the Physics Briefing Book, a scientific summary of the community’s input, prepared by the Physics Preparatory Group. The ESG converged on the final recommendations during a week-long drafting session held in Germany in January 2020.
A vision for the near- and long-term future
Originally scheduled to be published in May 2020, the current update was delayed by the COVID-19 pandemic, so that the resolution to update the Strategy was approved by the CERN Council at its June 2020 Meeting. It places priority on the successful completion of the High-Luminosity LHC over the coming decade, and begins to map out the potential landscape for research in Europe in the post LHC era, presenting a vision for both the near- and long-term future. The Strategy update recommends a so-called Higgs factory as the highest priority to follow the LHC, while pursuing a technical and financial feasibility study for a next-generation hadron collider in parallel, in preparation for the long-term. Maintaining the existing European support for neutrino physics in the USA and Japan is also strongly recommended. A very comprehensive report, it also covers areas of synergy with neighbouring fields such as astroparticle and nuclear physics, and it includes societal aspects ranging from training and knowledge transfer to minimising the environmental footprint of future facilities. Discover the full strategy update, and join us on the unfolding adventure of research at the frontier of knowledge.