This White Paper presents the science case of an Electron-Ion Collider (EIC), focused on the structure and interactions of gluon-dominated matter, with the intent to articulate it to the broader...

Two-particle azimuthal angle correlations have been proposed to be one of the most direct and sensitive probes to access the underlying gluon dynamics involved in hard scatterings. In anticipation of an electron-ion collider (EIC), detailed studies of dihadron correlation measurements in electron-proton and electron-ion collisions at an EIC have been performed. The impact of such measurements on the understanding of the different gluon distribution functions, as a clean signature for gluon saturation and to constrain saturation models further, has been explored. It is shown that dihadron correlation measurements will be one of the key methods to probe gluon saturation phenomena at a future EIC.

In this work, we present a systematic study on the feasibility of probing the largely unexplored transverse-momentum-dependent gluon Sivers function (GSF) in open charm production, and high-$p_T$ charged dihadron and dijet production at a future high-energy, high-luminosity electron-ion collider (EIC). The Sivers function is a measure for the anisotropy of the parton distributions in momentum space inside a transversely polarized nucleon. It is proposed that it can be studied through single spin asymmetries in the photon-gluon fusion subprocess in electron-proton collisions at the EIC. Using a well-tuned Monte Carlo model for deep inelastic scattering, we estimate the possible constraints of the GSF from the future EIC data. A comparison of all the accessible measurements illustrates that the dijet channel is the most promising way to constrain the magnitude of the GSF over a wide kinematic range.

A multiphase transport (AMPT) model has been successful in explaining a wide range of observables in relativistic heavy ion collisions. In this work, we implement a newer set of free proton parton distribution functions and an impact parameter-dependent nuclear shadowing in the AMPT model. After refitting the parameters of the two-component initial condition model to the experimental data on $pp$ and $p\overline{p}$ total and inelastic cross sections from $\sqrt{s}\sim$ 4 GeV to 13 TeV, we study particle productions in $pp$ and $AA$ collisions. We show that the updated AMPT model with string melting can reasonably describe the overall particle yields and transverse momentum spectra for both $pp$ and $AA$ collisions at RHIC and LHC energies after we introduce a nuclear scaling of the minijet transverse momentum cutoff for $AA$ collisions at LHC energies that is motivated by the color glass condensate. Since heavy flavor and $\mathrm{high}-p_{\mathrm{T}}$ particles are produced by perturbative-QCD processes and thus directly depend on parton distribution functions of nuclei, the updated AMPT model is expected to provide a more reliable description of these observables.

The upcoming electron-ion collider (EIC) will address several outstanding puzzles in modern nuclear physics. Topics such as the partonic structure of nucleons and nuclei, the origin of their mass and spin, among others, can be understood via the study of high-energy electron-proton ($ep$) and electron-nucleus ($eA$) collisions. Achieving the scientific goals of the EIC will require a novel electron-hadron collider and detectors capable to perform high-precision measurements but also dedicated tools to model and interpret the data. To aid in the latter, we present a general-purpose $eA$ Monte Carlo generator—BeAGLE. In this paper, we provide a general description of the models integrated into BeAGLE, applications of BeAGLE in $eA$ physics, implications for detector requirements at the EIC, and the tuning of the parameters in BeAGLE based on available experimental data. Specifically, we focus on a selection of model and data comparisons in particle production in both $ep$ and $eA$ collisions, where baseline particle distributions provide essential information to characterize the event. In addition, we investigate the collision geometry determination in $eA$ collisions, which could be used as an experimental tool for varying the nuclear density.