Vol. 8 (2025): Physics Briefing Book: Input for the 2026 update of the European Strategy for Particle Physics

Editors: Roger Forty, Karl Jakobs, Hugh Montgomery, Mike Seidel, and Paris Sphicas

The CERN Council established the European Strategy Group (ESG), which is responsible for submitting final recommendations to the Council for approval in early 2026. The Strategy Secretariat is in charge of organising the full process. In deriving the recommendations, the European Strategy for Particle Physics update should take into account the input of the particle physics community, progress in implementation of the 2020 Strategy update, and the accomplishments in recent years. These should include results from the LHC and other experiments or facilities worldwide, progress in the construction of the High-Luminosity LHC and physics expectations from its operation, the FCC Feasibility Study, and recent technological developments in accelerators, detectors, and computing. The Physics Preparatory Group (PPG) is to distill the community’s scientific input and the scientific discussion at the Open Symposium into the current “Physics Briefing Book”. This book is provided to the ESG as the foundation for their consideration during their five-day-long session for drafting the recommendations. The Physics Briefing Book is also shared with the particle physics community for their final input into the process. For the evaluation of the physics performance of the proposed colliders and experiments in other areas, benchmark processes and measurements have been defined by nine PPG working groups. The focus in this book is on the presentation and discussion of the performance against these benchmarks. The book does not aim to give a complete and comprehensive overview on the different physics and technology areas.