[Paper Review] A Plan for Electron Ion Collider in China

Xurong Chen|arXiv (Cornell University)|Sep 3, 2018

Particle physics theoretical and experimental studies6 references4 citations

TL;DR

This paper proposes the EicC (electron-ion collider) in China as a two-stage facility to study nucleon structure with high luminosity and polarized beams. It aims to precisely measure sea quark distributions, transverse momentum and generalized parton distributions, and probe exotic baryons with hidden charm and beauty, offering complementary insights to U.S. and European EIC programs with unique sensitivity to valence and sea quark dynamics at intermediate energies.

ABSTRACT

One of the frontier research areas common to both nuclear and particle physics is the study of hadron structure and the strong interaction. In this contribution we will discuss a plan for a polarized electron-ion collider in China (EicC) and its physics goals.

Motivation & Objective

• To establish a high-luminosity, polarized electron-ion collider in China to study the internal structure of nucleons.
• To measure sea quark distributions (1D, TMD, GPD) with unprecedented precision.
• To investigate exotic baryon states with hidden charm and beauty, including penta-quark states and bottomonium production.
• To probe non-perturbative gluon contributions and the proton mass mechanism via threshold measurements.
• To enable searches for new physics beyond the Standard Model through precision tests of lepton flavor violation and weak mixing angle.

Proposed method

• Design EicC in two stages: EicC-I (3–5 GeV e⁻, 12–30 GeV p⁺) and EicC-II (5–10 GeV e⁻, 60–100 GeV p⁺), both with polarized beams.
• Utilize the Heavy Ion High Intensity Accelerator Facility (HIAF) as the base infrastructure for accelerator construction.
• Implement high-luminosity operation (up to 1×10³⁵ cm⁻²s⁻¹ in EicC-II) to enable rare process detection.
• Employ polarized electron and ion beams to access spin-dependent parton distributions and TMDs.
• Conduct simulations of TMD Collins function asymmetry and cross sections for exclusive processes like ep → eN*⁺_{b¯b} → eΥ.
• Leverage high center-of-mass energy (up to 63 GeV in EicC-II) to probe large-W electroproduction of J/ψ and Υ.

Experimental results

Research questions

• RQ1 What are the precise 1D, TMD, and GPD distributions of sea quarks in the nucleon, and how do they differ from valence quarks?
• RQ2 Can the EicC-I facility resolve the quantum numbers of exotic baryons, such as hidden beauty penta-quarks?
• RQ3 How do gluon contributions and trace anomaly affect the proton mass, and can this be measured via Υ production near threshold?
• RQ4 What is the role of non-perturbative gluons in hadronization and proton spin structure?
• RQ5 Can EicC-II detect deviations from the Standard Model through precision measurements of charged lepton flavor violation or the weak mixing angle?

Key findings

• EicC-I provides a clean kinematic window for studying sea quarks and valence quarks, with center-of-mass energy √S ≈ 16 GeV and luminosity of 4×10³³ cm⁻²s⁻¹.
• The simulation shows that EicC-I can achieve very low uncertainty (small error bars) in TMD Collins function asymmetry across x, z, P_T, and Q² over a one-year run.
• EicC-I is well-suited for studying exotic baryons with hidden beauty, with a predicted total cross section of ~10 pb for ep → eN*⁺_{b¯b} → eΥ at √S > 16 GeV.
• EicC-I enables precision measurement of Υ production near threshold, reducing theoretical uncertainties due to the heavy bottom quark mass.
• EicC-II will extend the kinematic reach to explore gluon GPDs at large W via electroproduction of J/ψ and Υ, with luminosity up to 1×10³⁵ cm⁻²s⁻¹.
• The EicC program is complementary to JLab 12 GeV and U.S./European EIC initiatives, focusing on intermediate-x and intermediate-Q² regions where other facilities have limited coverage.