The Large Hadron–Electron Collider (LHeC) is designed to move the field of deep inelastic scattering (DIS) to the energy and intensity frontier of particle physics. Exploiting energy-recovery technology, it collides a novel, intense electron beam with a proton or ion beam from the High-Luminosity Large Hadron Collider (HL-LHC). The accelerator and interaction region are designed for concurrent electron–proton and proton–proton operations. This report represents an update to the LHeC’s conceptual design report (CDR), published in 2012. It comprises new results on the parton structure of the proton and heavier nuclei, QCD dynamics, and electroweak and top-quark physics. It is shown how the LHeC will open a new chapter of nuclear particle physics by extending the accessible kinematic range of lepton–nucleus scattering by several orders of magnitude. Due to its enhanced luminosity and large energy and the cleanliness of the final hadronic states, the LHeC has a strong Higgs physics programme and its own discovery potential for new physics. Building on the 2012 CDR, this report contains a detailed updated design for the energy-recovery electron linac (ERL), including a new lattice, magnet and superconducting radio-frequency technology, and further components. Challenges of energy recovery are described, and the lower-energy, high-current, three-turn ERL facility, PERLE at Orsay, is presented, which uses the LHeC characteristics serving as a development facility for the design and operation of the LHeC. An updated detector design is presented corresponding to the acceptance, resolution, and calibration goals that arise from the Higgs and parton-density-function physics programmes. This paper also presents novel results for the Future Circular Collider in electron–hadron (FCC-eh) mode, which utilises the same ERL technology to further extend the reach of DIS to even higher centre-of-mass energies.
We discuss the implications of assuming a four-zero Yukawa texture and a general Higgs potential for the production of neutral Higgs boson pairs at γγ colliders through the γγ → φiφj (φi = h, H, A) reaction within the context of the two Higgs doublet model type III. Exact analytical expressions for the γγ → φiφj reaction are presented. The use of a nonlinear R ξ -gauge, which considerably simplifies the loop calculations and renders compact analytical expressions, is stressed. We show that these processes are very sensitive to a general structure of the Higgs potential that impact the triple and quartic couplings of the scalar sector. We present results for scenarios of the parameters of the model that are still consistent with current experimental constraints. It is found that the cross sections for the γγ → φiφj processes can be up to two orders of magnitude larger than those gotten in 2HDM type I and type II. The possibility of a light CP-scalar is also studied.
We study the substantial enhancement, with respect to the corresponding Standard Model rates, that can be obtained for the branching ratios of the decay channels h → γγ and h → γZ within the framework of the Two Higgs Doublet Model Type III, assuming a four-zero Yukawa texture and a general Higgs potential. We show that these processes are very sensitive to the flavor pattern entering the Yukawa texture and to the triple coupling structure of the Higgs potential, both of which impact onto the aforementioned decays. We can accommodate the parameters of the model in such a way to obtain the h → γγ rates reported by the Large Hadron Collider and at the same time we get a h → γZ fraction much larger than in the Standard Model, indeed within experimental reach. We present some scenarios where this phenomenology is realized for spectrum configurations that are consistent with current constraints. We also discuss the possibility of obtaining a light charged Higgs boson compatible with all such measurements, thereby serving the purpose of providing a hallmark signal of the scenario considered.
We obtain limits on the quartic neutral gauge bosons couplings Zγγγ and ZZγγ using LEP 2 data published by the L3 Collaboration on the reactions e + e − → γγγ, Zγγ. We also obtain 95 % C. L. limits on these couplings at the future linear colliders energies. The LEP 2 data induce limits of order 10 −5 GeV −4 for the Zγγγ couplings and of order 10 −3 GeV −2 for the ZZγγ couplings, which are still above the respective Standard Model predictions. Future e + e − linear colliders may improve these limits by one or two orders of magnitude.
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