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.

No abstract

Pseudo-Goldstone dark matter coupled to the Standard Model via the Higgs portal offers an attractive framework for phenomenologically viable pseudo-scalar dark matter. It enjoys natural suppression of the direct detection rate due to the vanishing of the relevant (tree level) Goldstone boson vertex at zero momentum transfer, which makes light WIMP-like dark matter consistent with the strong current bounds. In this work, we explore prospects of detecting pseudo-Goldstone dark matter at the LHC, focusing on the vector boson fusion (VBF) channel with missing energy. We find that, in substantial regions of parameter space, relatively light dark matter (mχ < 150 GeV) can be discovered in the high luminosity run as long as it is produced in decays of the Higgs-like bosons.

We study the possibility of a light Dark Matter (DM) within a constrained Minimal Supersymmetric Standard Model (cMSSM) framework augmented by a SM singletpair sector to account for the non-zero neutrino masses by inverse seesaw mechanism. Working within a 'hybrid' scenario with the MSSM sector fixed at high scale and the singlet neutrino sector at low scale, we find that, contrary to the case of the usual cMSSM where the neutralino DM cannot be very light, we can have a light sneutrino DM with mass below 100 GeV satisfying all the current experimental constraints from cosmology, collider as well as low-energy experiments. We also note that the supersymmetric inverse seesaw mechanism with sneutrino as the lightest supersymmetric partner can have enhanced samesign dilepton final states with large E T / coming from the gluino-and squark-pair as well as the squark-gluino associated productions and their cascade decay through charginos. We present a collider study for the same-sign dilepton+jets+E T / signal in this scenario and propose some distinctions with the usual cMSSM. We also comment on the implications of such a light DM scenario on the invisible decay width of an 125 GeV Higgs boson.

We consider the production of a heavy neutrino and its possible signals at the Large Hadronelectron Collider (LHeC) in the context of an inverse-seesaw model for neutrino mass generation. The inverse seesaw model extends the Standard Model (SM) particle content by adding two neutral singlet fermions for each lepton generation. It is a well motivated model in the context of generating non-zero neutrino masses and mixings. The proposed future LHeC machine presents us with a particularly interesting possibility to probe such extensions of the SM with new leptons due to the presence of an electron beam in the initial state. We show that the LHeC will be able to probe an inverse scenario with much better efficacy compared to the LHC with very nominal integrated luminosities as well as exploit the advantage of having the electron beam polarized to enhance the heavy neutrino production rates.

The breaking of parity, a fundamental symmetry between left and right is best understood in the framework of left-right symmetric extension of the standard model. We show that the production of a heavy right-handed neutrino at the proposed Large Hadron-Electron Collider (LHeC) could give us the most simple and direct hint of the scale of this breaking in left-right symmetric theories. This production mode gives a lepton number violating signal with ∆L = 2 which is very clean and has practically no standard model background. We highlight that the right-handed nature of WR exchange which defines the left-right symmetric theories can be confirmed by using a polarized electron beam and also enhance the production rates with relatively lower beam energy.

It is well known that for the pure standard model triplet fermionic WIMP-type dark matter (DM), the relic density is satisfied around 2 TeV. For such a heavy mass particle, the production cross-section at 13 TeV run of LHC will be very small. Extending the model further with a singlet fermion and a triplet scalar, DM relic density can be satisfied for even much lower masses. The lower mass DM can be copiously produced at LHC and hence the model can be tested at collider. For the present model we have studied the multi jet (≥ 2 j) + missing energy ( E T ) signal and show that this can be detected in the near future of the LHC 13 TeV run. We also predict that the present model is testable by the earth based DM direct detection experiments like Xenon-1T and in future by Darwin.

Recent CMS searches for dileptoquark production report local excesses of 2Ao in an eejj channel and 2.6a in an eprjj channel. Here, we simultaneously explain both excesses with resonant slepton production in 72-parity violating supersymmetry. We consider resonant slepton production, which decays to a lepton and a chargino/neutralino, followed by three-body decays of the neutralino/chargino via an 72-parity violating coupling. There are regions of parameter space which are also compatible at the 95% confidence level with a 2.8a eejj excess in a recent CMS WR search, while being compatible with other direct search constraints. Phase II of the GERDA neutrinoless double beta decay (Duft/S) experiment will probe a sizable portion of the good-fit region. The recent CM S search for dileptoquark production found, with a certain set o f cuts, a 2.4cr local excess in the eejj channel and a 2.6 c local excess in an ePT j j channel1 in com parison to Standard M odel (SM ) expect ations. The CM S searches use pp collision data at the Large H adron C ollider (LHC) and a center o f mass energy o f 8 TeV and 19.6 f t r 1 o f integrated luminosity. Requiring a certain set o f cuts (called "MLq = 650 G eV " cuts), CMS reported 36 events on a background2 o f 20.5 ± 3.5 in the eejj channel, and 18 events on a background o f 7.5 ± 1 .6 in the evjj channel [1]. Taken sim ultaneously and ignoring correlations betw een the systematics, these excesses am ount to a 3.5cr effect. In addition, a WR search (with different cuts to the dileptoquark search) reported a 2.80-excess in the eejj channel at 1.8 TeV < Meejj < 2.2 TeV [2]. These excesses are not significant enough to claim a discovery, or even evidence. They are sim ilar enough to attem pt a unified explanation of all three, and a timely explanation before the next LHC run (ran II) in terms of new physics such that further tests can be applied and analysis strategies can be set for run II.There have been a few attempts to explain the CMS excesses with different models. Coloron-assisted leptoquarks were proposed in Ref. [3]. The WR excess was interpreted in grand unified theory m odels in Refs. [4,5], In Ref. [6], pair production o f vectorlike leptons was proposed via W '/Z ' vector bosons. Reference [7] perform ed a detailed analysis (including a general flavor structure) of W'/Z' interpretations o f the WR search data. In Ref. [8], it was supposed that leptoquarks consistent with the 1 CMS refers to this channel as evjj, and we shall from here use the same nomenclature. 2We have added systematic and statistical errors in quadrature. dileptoquark excess decay into dark m atter particles with a significant branching ratio. Reference [9] explains the dileptoquark excesses with di-sbottom production, fol lowed by 72-parity violating (RPV) decay. In a previous article [10], w e proposed that resonant slepton production was responsible for the WR search excess in RPV supersymmetry. One o f us showed that this explanation is also consistent with recent deviations from SM prediction m easur...