The LHeC Detector
The current default LHeC detector design is shown in the picture below. In this arrangement, the more energetic proton beam comes from the right and the electron beam from the left. Due to the large energy imbalance there is a much denser and more energetic particle flow in the proton beam direction (forward), which determines the difference in inner tracking and forward/backward calorimetry. The detector as sketched here is about 14m long in z direction, parallel to the beam axis, and it has an approximate outer radius of 4.5m, which is achieved with a solenoid field of 3.5T. Current efforts, as of 2014, are directed to an optimisation of the forward tracking and to a full simulation of the detector to replace simplifying parameterisations as have often been used in previous LHeC physics studied. The detector components have presently been based on rather classic techniques such as Silicon pixel and strip tracking and Liquid Argon electromagnetic calorimetry, for example. The detector needs to be complemented by tagging devices in forward direction, for protons and neutrons, and in backward direction, for photons and low momentum transfer electrons.
The FCC_he Detector
The design of a detector for the hadron-electron (he) configuration of the Future Circular Collider (FCC) can to some approximation be obtained by considering the LHeC detector when one adjusts for the much enlarged proton beam energy. The longitudinal FCC_he detector dimensions roughly scale proportional to the logarithm of the ratio of the proton beam energies in forward direction (ln50/7 = 2) and of the electron beam energies in backward direction (1.. 1.3). At these very high energies rare processes, such as the H → μμ decay, may require more attention to the muon momentum measurement, which is, in this example, why one may consider a double solenoid structure embedding the muon detector. The dimensions of such a device would be comparable to those of the CMS detector currently operating at the LHC. The choices of technology will surely be adapted when the time approaches to build an FCC_he detector. However, they would be available already today because an ep environment is less demanding than a pp environment in terms of radiation hardness and pile-up of interactions.