CERN Yellow Reports: Monographs, Vol. 4 (2025): Report from the Conventional Beams Working Group to the Physics Beyond Colliders Study and to the 2026 European Strategy for Particle Physics Update

This document reports the work and results of the Conventional Beams Working Group, which focuses on studies of the beam-related and technical requirements and requests from proposals submitted to the Physics Beyond Colliders Study (PBC) for the North Area at the CERN SPS and the East Area at the CERN PS accelerators. Previous CBWG reports have been published in 2018 and 2022, providing inputs to the European Strategy for Particle Physics (ESPP) discussions that took place in those years.This new document provides updated and supplementary material relevant for the 2025–2026 ESPP Update, including detailed results regarding the HIKE, SHADOWS, DICE/NA60+, ENUBET, NuTag,and SBN projects. Please note that BDF/SHiP was studied in an independent PBC Working Group. Since its inception, the working group has presented results on feasibility, requirements, compatibility between proposals, and, where possible, cost estimates at all PBC Annual Workshops and group meetings.Following the renewed mandate of the PBC Study in 2021, the Conventional Beams Working Group continued its studies for previously received proposals, as well as for new initiatives, including ENUBET, NuTag, a potential Short-Baseline tagged neutrino beam (SBN), SHADOWS, and HIKE. Work relevant to these studies has progressed since the Annual PBC Workshop in 2019 [5], which this document summarises. This edition also includes information on installation work already carried out for some proposals and presents initial studies for the more recent ones.The physics interest, sensitivity reach, and worldwide competitiveness of the proposals are discussed in the PBC working groups for Beyond Standard Model (BSM) physics and Quantum Chromo Dynamics(QCD), as well as in the newly established working group on Feebly Interacting Particles (FIPs). These physics-focused working groups collaborate in close synergy with the Conventional Beams Working Group.