Exploring the Energy Frontier with Deep Inelastic Scattering at the LHC A Contribution to the Update of the European Strategy on Particle Physics

This text is an Addendum to the paper of the same title submitted on the LHeC, and the ERL development facility PERLE, to the European Particle Physics Strategy Update. Adding an electron-hadron scattering experiment to the LHC is expected to attract a collaboration strong enough to build and operate one extra LHC detector for concurrent eh and hh operation. The LHeC programme is of strong interest for the LHC community at large because of the striking synergy of eh with hh physics as described in the main paper. The present Addendum briefly describes the current ep/eA detector concept, and a timeline of its two-year installation is presented, which is commensurate with typical LHC shutdown durations. The ep interaction is free of pile-up and the event configuration cleaner than in pp, which tames the computing requirements for this detector with respect to the GPDs. Building and installing the ERL is estimated to take roughly a decade, which is consistent with the LHC future. The luminosity performance and operation profile are discussed, following recent official statements by CERN. Two ERL configurations are presented for electron beam energies ranging from 50 to 60 GeV, together with a physics evaluation of the importance to keep the electron energy high and a summary of the accelerator components in both cases. The cost is estimated to be around 1 billion CHF, subject to a final physics-energy-effort-cost optimisation at a suitable future time when the cost of the series production of the 802 MHz cavity-cryo modules can be more reliably determined. An Appendix sketches the design of the interaction region serving three beams. The LHeC physics, detector and machine developments, post the 2012 CDR, will be outlined in more detail in a report to appear in early 2019.