High-energy Electron-Ion Collider Research Articles

Electroproduction of a large invariant mass photon pair

We study the exclusive electroproduction of a photon pair in the kinematical regime where the diphoton invariant mass is large and where the nucleon flies almost in its original direction. We discuss the relative importance of the QCD process where the two photons originate from a quark line compared to the single (double) Bethe-Heitler processes where one (two) photons originate from the lepton line. This process turns out to be a promising tool to study generalized parton distributions in the nucleon, both at the medium energy of JLab and at a high energy electron ion collider.

Gluon TMDs in Quarkonium Production

Quarkonium production offers good possibilities to study gluon TMDs. In this proceedings contribution this topic is explored for the linearly polarized gluons inside unpolarized hadrons and unpolarized gluons inside transversely polarized hadrons. It is argued that chi _{b0/2} and eta _b production at LHC are best to study the effects of linearly polarized gluons in hadronic collisions, by means of angular independent ratios of ratios of cross sections. This can be directly compared to cos 2phi asymmetries in heavy quark pair and dijet production in DIS at a future high-energy Electron-Ion Collider (EIC), which probe the same TMDs. In the small-x limit this corresponds to the Weizsäcker–Williams (WW) gluon distributions, which should show a change in behavior for transverse momenta around the saturation scale. Together with investigations of the dipole (DP) gluon distributions, this can provide valuable information about the polarization of the Color Glass Condensate if sufficiently small x-values are reached. Quarkonia can also be useful in the study of single transverse spin asymmetries. For transversely polarized hadrons the gluon distribution can be asymmetric, which is referred to as the Sivers effect. It leads to single spin asymmetries in for instance J{/}psi (pair) production at AFTER@LHC, which probe the WW or f-type gluon Sivers TMD. It allows for a test of a sign-change relation w.r.t. the gluon Sivers TMD probed at an EIC in open heavy quark pair production. Single spin asymmetries in backward inclusive C-odd quarkonium production, such as J{/}psi production, may offer probes of the DP or d-type gluon Sivers TMD at small x-values in the polarized proton, which in that limit corresponds to a correlator of a single Wilson loop, describing the spin-dependent odderon.

Science and status of the Electron Ion Collider

The US Nuclear Science Advisory Committee (NSAC) recently recommended the construction of a high-luminosity, high-energy Electron Ion Collider (EIC), with polarized beams capable of colliding polarized electrons with polarized proton and light ion beams, and with any nucleus. The [Formula: see text] range between 40[Formula: see text]GeV and 140[Formula: see text]GeV, and luminosity range from [Formula: see text] were recommended. It is anticipated that under the current guidance from the DOE, the collider could become operational in the second half of the 2020’s. This paper summarizes its science and the scope of this over all project.

Gluon TMD studies at EIC

A high-energy Electron-Ion Collider (EIC) would offer a most promising tool to study in detail the transverse momentum distributions of gluons inside hadrons. This applies to unpolarized as well as linearly polarized gluons inside unpolarized protons, and to left-right asymmetric distributions of gluons inside transversely polarized protons, the so-called gluon Sivers effect. The inherent process dependence of these distributions can be studied by comparing to similar, but often complementary observables at LHC.

Heavy quark production in deep inelastic electron-nucleus scattering

Heavy quark production has been very well studied over the last years both theoretically and experimentally. Theory has been used to study heavy quark production in $e p$ collisions at HERA, in $pp$ collisions at Tevatron and at RHIC, in $pA$ and $dA$ collisions at RHIC and in $AA$ collisions at CERN-SPS and at RHIC. However, to the best of our knowledge, heavy quark production in $eA$ has received almost no attention. With the possible construction of a high energy electron-ion collider, updated estimates of heavy quark production are needed. We address the subject from the perspective of saturation physics and compute the heavy quark production cross section with the dipole model. We isolate shadowing and non-linear effects, showing their impact on the charm structure function and on the transverse momentum spectrum.

Understanding saturation and AA collisions with an eA collider

The initial conditions in high energy nucleus-nucleus collisions are determined by the small momentum fraction part of the nuclear wavefunction. This is the regime of gluon saturation and the most direct way to experimentally study it would be deep inelastic scattering at a high energy electron ion collider (EIC). This talk discusses some of the connections between physics at the EIC and the initial stage of relativistic heavy ion collisions. We argue that measurements at an EIC will provide detailed high-precision information about the parameters for the initial conditions, transverse geometry and longitudinal correlations that will be crucial in understanding the initial stage of a heavy ion collision.

A new high-energy electron–ion collider: High precision QCD structure and beyond

A new high-energy electron–ion collider is discussed which will allow unprecedented study of the quark and gluon structure of the proton as well as nuclei. Using polarized beams one will be able to explore the polarized quark and gluon distributions of the nucleon at the few percent level, especially the strange and light quark sea components. Collider kinematics and excellent detection capabilities will enable careful study of the process by which a fast colored quark materializes into a group of energetic hadrons without color. Collisions with heavy nuclei, never before achieved at high center-of-mass energies, will allow the study of quantum chromodynamics (QCD) at extremes of gluon density. In addition to the physics program, the existing accelerator options under consideration are presented, as well as the current design of the interaction region spectrometer.

STUDY OF THE FUNDAMENTAL STRUCTURE OF MATTER WITH AN ELECTRON-ION COLLIDER

▪ Abstract We present an overview of the scientific opportunities that would be offered by a high-energy electron-ion collider. We discuss the relevant physics of polarized and unpolarized electron-proton collisions and of electron-nucleus collisions. We also describe the current accelerator and detector plans for a future electron-ion collider. This review is dedicated to the memory of Professor Vernon W. Hughes.