A Second EIC Detector: Physics Case and Conceptual Design

TL;DR

The paper makes the case for a second general-purpose EIC detector and a separate interaction region to broaden physics reach and enhance robustness through independent cross-checks. It surveys physics opportunities enabled by alternative detector technologies and by IR-8 with a secondary focus, and translates these into detector-level performance targets and conceptual layouts. Key contributions include analyses of incoherent diffractive vetoing with ZDC/RP at a secondary focus, isotope-tagging prospects, and SMEFT/BSM sensitivity studies, alongside concrete detector concepts featuring mixed silicon-gaseous tracking, xpDIRC hpRICH, dual-readout HCAL, and SciGlass/LYSO EM calorimetry. The work identifies essential R&D needs (GridPix, Mini-DIRC for Z-tagging, fast timing, and software infrastructure) and highlights overlaps with Belle II and FCC-ee that can accelerate technology development and risk reduction. Overall, the report provides a technically grounded roadmap for a future second EIC detector that complements ePIC by diversifying technologies, improving forward instrumentation, and enabling novel measurements across the EIC program.

Abstract

This document is the closeout report for LDRD 23-050, a type-A LDRD project awarded in FY2022 under the title "A Second EIC Detector: Physics Case and Conceptual Design". The project was motivated by the strong interest within the EIC community in a second general-purpose detector and interaction region, and by the recognition that such a detector is essential to fully exploit the scientific potential of the EIC over its multi-decade lifetime. The key goals of the LDRD were to (i) strengthen the case for a second EIC detector, building on the community Yellow Report; (ii) develop a realistic detector concept complementary to the project detector, ePIC, in terms of physics reach, precision, and control of systematics; and (iii) broaden the overall EIC physics program. Since a possible second detector is expected to be realized with a delay of several years relative to the first detector, the project explicitly aimed at identifying technologies that are not yet sufficiently mature for ePIC but could be deployed on the later timescale of a second detector, thereby providing genuine complementarity and room for innovation. As envisioned in the original proposal, the expected outcome was a document detailing the physics potential and requirements of a second EIC detector, accompanied by a conceptual design and an outline of the remaining R&D needs. This report summarizes progress toward these goals, consolidating the physics studies, detector concepts, and technology assessments developed under this LDRD, and situating them within the broader context of worldwide detector R&D. Despite evolving EIC priorities and the effort devoted to ePIC, the work documented here is intended to provide a foundation and reference for future efforts toward a second detector. We hope this report will serve as a useful guide for colleagues advancing this program in the near- and mid-term future.

Figures (42)

• Figure 1: Full layout of the first interaction region (IR-6) featuring a 25 mrad crossing angle and the associated beamline instrumentation. Taken from PhysRevD.111.072013.
• Figure 2: Schematic layout of the second interaction region (IR-8) with a 35 mrad crossing angle, illustrating the lattice design, potential detector locations, and the position of the secondary beam focus. Taken from PhysRevD.111.072013.
• Figure 3: Coherent (red) and incoherent (blue) cross section for diffractive $J/\Psi$ vector meson production in e + Au collisions, assuming nominal resolution in the range $1 < Q^{2} < 10$ GeV$^2$. Adapted from ABDULKHALEK2022122447.
• Figure 4: Left: Number of non-vetoed incoherent diffractive events in ePb collisions as a function of momentum transfer $t$. The black curve shows all incoherent events; the blue curve shows events surviving after ZDC tagging and vetoing; the red curve shows events surviving after both ZDC and Roman Pot (RP) tagging and vetoing. Right: Vetoing power as a function of $t$, where each curve represents the inefficiency histogram of a given veto selection normalized to the total incoherent sample. Only selections with significant impact are shown. The term "RPSF" refers to the Roman Pot located at the Secondary Focus. Adapted from PhysRevD.111.072013.
• Figure 5: Left: Fragment $Z$ vs. hit position in the first RP for IR1. Right: Fragment $Z$ vs. hit position for a RP located near the secondary focus for IR2. The gray box on each plot shows the 10$\sigma$ beam exclusion area, using the beam parameters in table 3.5 of the 2021 EIC CDR osti_1765663. The plots are made assuming a $^{238}$U beam, with both known and predicted nuclear isotopes included as data points.