The FP420 Project: The challenge of measuring forward protons at the LHC

FP420 is an R and D project to assess the feasibility of installing proton detectors at 420m from the ATLAS and/or CMS interaction point(s) at the LHC. They would function as new sub-detectors, allowing the measurement of the spatial position and arrival time of protons scattered at very low angles with fractional momentum loss between 0.2% and 2%. Forward proton tagging in this region is expected to open a new programme of electroweak, QCD and beyond-the-Standard-Model physics. The challenges of the project are presented, along with the solutions envisaged, notably for the replacement cryostat, the detectors, the moving mechanism to bring the detectors close to the beam, and the alignment