Overview on Efforts for a Second Detector at the Electron-Ion Collider (EIC)

TL;DR

This work analyzes the motivation and design implications of adding a second general-purpose detector at the EIC beyond the baseline ePIC. It emphasizes cross-checking, cross-calibration, and reduced systematics achievable by independent measurements from two detectors with complementary technologies. A main focus is the IR-8 concept, which improves forward acceptance and low-pT reach, enabling enhanced exclusive, diffractive, and tagging measurements. Overall, the proposal aims to broaden the EIC physics program, increase robustness, and raise discovery potential by diversifying detector technologies and interaction-region configurations.

Abstract

The Electron-Ion Collider (EIC) will provide a unique experimental platform to explore the properties of gluons in nucleons and nuclei, offering new insights into their structure and dynamics. The EIC community has outlined a detailed physics program and the demanding detector requirements in a comprehensive detailed document. The primary general-purpose detector, ePIC, is designed to support a broad range of physics studies. However, there is strong community support for a second detector at the EIC to further enhance the scientific capabilities of the facility. A second detector would provide cross-checks and systematic controls for potential discoveries, while incorporating complementary technologies to address physics measurements that may be underrepresented by ePIC. In particular, it would improve forward detector acceptance at low transverse momentum ($p_T$) and enable more precise measurements in exclusive, diffractive, and tagging physics. This talk will provide a general overview of the second detector and outline its potential capabilities, highlighting key areas of the physics program it could enhance.

Figures (2)

• Figure 1: Schematic layout of the second interaction region (IR-8), designed with a 35 mrad crossing angle. The diagram illustrates the accelerator lattice, potential detector locations, and the position of the secondary beam focus along the hadron beamline. Adapted from PhysRevD.111.072013
• Figure 2: Left: Number of non-vetoed incoherent diffractive events in ePb collisions as a function of momentum transfer $t$. The black curve represents all incoherent events; the blue curve shows events remaining after tagging and vetoing by the Zero Degree Calorimeter (ZDC); the red curve corresponds to events surviving after combined tagging and vetoing by both the ZDC and the Roman Pot (RP). Right: Vetoing efficiency as a function of $t$, where each curve depicts the inefficiency histogram of a specific veto selection normalized to the total incoherent event sample. Only veto selections with significant impact are shown. The term “RPSF” denotes the Roman Pot located at the Secondary Focus. Adapted from PhysRevD.111.072013.