A Large Hadron Electron Collider at CERN Report on the Physics and Design Concepts for Machine and Detector

Abstract

The physics programme and the design are described of a new collider for particle and nuclear physics, the Large Hadron Electron Collider (LHeC), in which a newly built electron beam of 60 GeV, to possibly 140 GeV, energy collides with the intense hadron beams of the LHC. Compared to the first ep collider, HERA, the kinematic range covered is extended by a factor of twenty in the negative four-momentum squared, Q 2 , and in the inverse Bjorken x, while with the design luminosity of 10 33 cm −2 s −1 the LHeC is projected to exceed the integrated HERA luminosity by two orders of magnitude. 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 measurements. These are designed to investigate a variety of fundamental questions in strong and electroweak interactions. The LHeC thus continues the path of deep inelastic scattering (DIS) into unknown areas of physics and kinematics. The physics programme also includes electron-deuteron and electron-ion scattering in a (Q 2 1/x) range extended by four orders of magnitude as compared to previous lepton-nucleus DIS experiments for novel investigations of neutron's and nuclear structure, the initial conditions of Quark-Gluon Plasma formation and further quantum chromodynamic phenomena. 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 including new dipole prototypes, cryogenics, RF, 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-ofthe 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 beam pipe. Civil engineering and installation studies are presented for the accelerator and the detector. The LHeC can be built within a decade and thus be operated while the LHC runs in its high-luminosity phase. It so represents a major opportunity for progress in particle physics exploiting the investment made in the LHC.

Exclusive photoproduction of a γ ρ pair with a large invariant mass

“…We would like to mention that a similar study could be performed in principle in the Compass experiment at CERN where S γN ∼ 200 GeV 2 and at LHC in ultraperipheral collisions [49], as well as in future electron proton collider projects like EIC [50] and LHeC [51]. …”

Sterile neutrino searches at future e−e+, pp and e−p colliders

“…They allow for a cleaner collision environment compared to the pp colliders and for higher center-ofmass energies than the e − e + colliders. Currently, a future e − p collider is discussed as an upgrade of the LHC, the Large Hadron-electron Collider (LHeC), which comprises a 60 GeV electron beam and possible electron polarization of up to 80% [101][102][103] that will collide with the 7 TeV proton beam inside the LHC tunnel. The machine is planned to deliver up to 100 fb −1 integrated luminosity per year at a center-of-mass energy of ∼ 1.0 TeV, collecting ∼1 ab −1 over its lifetime.…”

Nuclear structure functions at a future electron-ion collider

“…In order to have a cleaner probe of the partonic structure of nuclei and to extend the current measurements down to smaller x, a next-generation DIS experiment is called for. To this end, two possibilities have been entertained: the LHeC collider at CERN [23] and an EIC in the United States [24]. In this paper, we will focus on the EIC project and its potential to improve the precision of nuclear PDFs.…”