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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.

Understanding the origin and dynamics of hadron structure and in turn that of atomic nuclei is a central goal of nuclear physics. This challenge entails the questions of how does the roughly 1 GeV mass-scale that characterizes atomic nuclei appear; why does it have the observed value; and, enigmatically, why are the composite Nambu-Goldstone (NG) bosons in quantum chromodynamics (QCD) abnormally light in comparison? In this perspective, we provide an analysis of the mass budget of the pion and proton in QCD; discuss the special role of the kaon, which lies near the boundary between dominance of strong and Higgs mass-generation mechanisms; and explain the need for a coherent effort in QCD phenomenology and continuum calculations, in exa-scale computing as provided by lattice QCD, and in experiments to make progress in understanding the origins of hadron masses and the distribution of that mass within them. We compare the unique capabilities foreseen at the electron-ion collider (EIC) with those at the hadron-electron ring accelerator (HERA), the arXiv:1907.08218v2 [nucl-ex] Rikutaro Yoshida (ryoshida@jlab.org) INTRODUCTIONAtomic nuclei lie at the core of everything we can see; and at the first level of approximation, their atomic weights are simply the sum of the masses of all the neutrons and protons (nucleons) they contain. Each nucleon has a mass m N ∼ 1 GeV, i.e. approximately 2000-times the electron mass. The Higgs boson produces the latter, but what produces the masses of the neutron and proton? This is the crux: the vast majority of the mass of a nucleon is lodged with the energy needed to hold quarks together inside it; and that is supposed to be explained by QCD, the strong-interaction piece within the Standard Model.QCD is unique. It is a fundamental theory with the capacity to sustain massless elementary degrees-of-freedom, viz. gluons and quarks; yet gluons and quarks are predicted to acquire mass dynamically [1][2][3], and nucleons and almost all other hadrons likewise, so that the only massless systems in QCD are its composite NG bosons [4,5], e.g. pions and kaons. Responsible for binding systems as diverse as atomic nuclei and neutron stars, the energy associated with the gluons and quarks within these Nambu-Goldstone (NG) modes is not readily apparent. This is in sharp and fascinating contrast with all other "everyday" hadronic bound states, viz. systems constituted from up = u, down = d, and/or strange = s quarks, which possess nuclear-size masses far in excess of anything that can directly be tied to the Higgs boson. 1

Recent high precision experimental data from a variety of hadronic processes opens new opportunities for determination of the collinear parton distribution functions (PDFs) of the proton. In fact, the wealth of information from experiments such as the Large Hadron Collider (LHC) and others, makes it difficult to quickly assess the impact on the PDFs, short of performing computationally expensive global fits. As an alternative, we explore new methods for quantifying the potential impact of experimental data on the extraction of proton PDFs. Our approach relies crucially on the correlation between theory-data residuals and the PDFs themselves, as well as on a newly defined quantity -the sensitivity -which represents an extension of the correlation and reflects both PDF-driven and experimental uncertainties. This approach is realized in a new, publicly available analysis package PDFSENSE, which operates with these statistical measures to identify particularly sensitive experiments, weigh their relative or potential impact on PDFs, and visualize their detailed distributions in a space of the parton momentum fraction x and factorization scale µ. This tool offers a new means of understanding the influence of individual measurements in existing fits, as well as a predictive device for directing future fits toward the highest impact data and assumptions. XXVI International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS2018)16-20 April 2018 Kobe, Japan * The webpage for the PDFSense tool is: https://metapdf.hepforge.org/PDFSense/ We acknowledge the hospitality of CERN, DESY, and Fermilab where a portion of this work was performed.

We perform a comprehensive analysis of the role of nonperturbative (or intrinsic) charm in the nucleon, generated through Fock state expansions of the nucleon wave function involving fivequark virtual states represented by charmed mesons and baryons. We consider contributions from a variety of charmed meson-baryon states and find surprisingly dominant effects from theD * 0 Λ + c configuration. Particular attention is paid to the existence and persistence of high-x structure for intrinsic charm, and the x dependence of the c −c asymmetry predicted in meson-baryon models. We discuss how studies of charmed baryons and mesons in hadronic reactions can be used to constrain models, and outline future measurements that could further illuminate the intrinsic charm component of the nucleon.

We reply to the Comment of Brodsky and Gardner, pointing out a number of incorrect claims about our fitting methodology, and elaborate how global QCD analysis of all available high-energy data provides no evidence for large intrinsic charm in the nucleon.

We present a new global QCD analysis of parton distribution functions, allowing for possible intrinsic charm (IC) contributions in the nucleon inspired by light-front models. The analysis makes use of the full range of available high-energy scattering data for Q 2 1 GeV 2 and W 2 3.5 GeV 2 , including fixed-target proton and deuteron cross sections at lower energies that were excluded in previous global analyses. The expanded data set places more stringent constraints on the momentum carried by IC, with x IC at most 0.5% (corresponding to an IC normalization of ∼ 1%) at the 4σ level for ∆χ 2 = 1. We also critically assess the impact of older EMC measurements of F c 2 at large x, which favor a nonzero IC, but with very large χ 2 values.There has been considerable interest recently in the nature of Fock states of the proton wave function involving five or more quarks, such as |uudqq , where q = u, d, s or c [1][2][3][4][5][6]. This has arisen partly from attempts to understand flavor asymmetries observed in the nucleon sea, such asd >ū [7,8] and s =s [9], which clearly point to a nonperturbative origin. In addition, there has been a long-standing debate about the existence of intrinsic charm (IC) quarks in the proton, associated with the |uudcc component of the proton wave function.Aside from the intrinsic interest in the role of nonperturbative dynamics in the structure of the nucleon sea, the leptoproduction of charm quarks is also important in providing information on the gluon distribution in the nucleon. A significant IC component in the nucleon wave function could also influence observables measured at the LHC, either directly through enhanced cross sections at large x, or indirectly via the momentum sum rule leading to a decreased momentum fraction carried by gluons.Following early indications from measurements of charm production in pp scattering of an anomalous excess of D mesons at large values of Feynman x F (see [10] and references therein), the proposal was made that the observed enhancement could be accounted for with the addition of intrinsic cc pairs in the nucleon that were not generated through perturbative gluon radiation [11]. Neglecting quark transverse momentum and assuming a charm mass much greater than other mass scales, Brodsky, Hoyer, Peterson and Sakai (BHPS) [11] derived an analytic approximation to the IC distribution that, unlike the perturbatively generated charm, was peaked at relatively large parton momentum fractions x.A number of experimental and theoretical studies have since sought to elucidate this issue, although the evidence has been somewhat inconclusive. Measurements of the charm structure function F [16] employed a hybrid scheme to interpolate between massless evolution at large Q 2 and PGF at low Q 2 , using the BHPS IC model and a model based on fluctuations of the nucleon to charmed baryon and D meson states [17][18][19]. While it was difficult to fit the data simultaneously in terms of a single IC framework, Steffens et al. found a slight preference for IC in the meso...

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