A Large Hadron Electron Collider at CERN, Physics, Machine, Detector

The physics programme and the design are described of a new electron-hadron collider, the LHeC, in which electrons of $60$ to possibly $140$\,GeV collide with LHC protons of $7000$\,GeV. With an $ep$ design luminosity of about $10^{33}$\,cm$^{-2}$s$^{-1}$, the Large Hadron Electron Collider exceeds the integrated luminosity collected at HERA by two orders of magnitude and the kinematic range by a factor of twenty in the four-momentum squared, $Q^2$, and in the inverse Bjorken $x$. The physics programme is devoted to an exploration of the energy frontier, complementing the LHC and its discovery potential for physics beyond the Standard Model with high precision deep inelastic scattering (DIS) measurements. These are projected to solve a variety of fundamental questions in strong and electroweak interactions. The LHeC thus becomes the world's cleanest high resolution microscope, designed to continue the path of deep inelastic lepton-hadron scattering into unknown areas of physics and kinematics. The physics programme also includes electron-ion (eA) scattering into a $(Q^2,~1/x)$ range extended by four orders of magnitude as compared to previous lepton-nucleus DIS experiments. The LHeC may be realised either as a ring-ring or as a linac-ring collider. Optics and beam dynamics studies are presented for both versions, along with technical design considerations on the interaction region, magnets, cryogenics, RF, civil engineering and further components. A design study is also presented of a detector suitable to perform high precision DIS measurements in a wide range of acceptance using state-of-the art detector technology, which is modular and of limited size enabling its fast installation. The detector includes tagging devices for electron, photon, proton and neutron detection near to the beampipe. The LHeC is designed to be built and operated while the LHC runs. It is a major opportunity for progress in particle physics and further exploits the investment made in the LHC.