---
title: 'EicC: Electron-Ion Collider in China'
url: https://www.emergentmind.com/topics/electron-ion-collider-in-china-eicc
type: topic
---

# EicC: Electron-Ion Collider in China

The Electron-Ion Collider in China (EicC) is a planned high-luminosity, high-precision lepton-hadron collider facility designed to enable advanced studies of nucleon and nuclear structure in Quantum Chromodynamics (QCD). Its experimental program necessitates sophisticated particle detection systems, with electromagnetic calorimetry playing a pivotal role in electron and photon measurement, particle identification (PID), and the resolution of complex final states.

## 1. EicC Electromagnetic Calorimeter: Architecture and Segmentation

The electromagnetic calorimeter (ECAL) at EicC is engineered as a multi-component system, each segment optimized for distinct kinematic coverage and detection demands:

- **Electron-Endcap Region**: Employs high-resolution, pure cesium iodide (pCsI) crystal calorimetry, targeting the most stringent demands in energy and position resolution for scattered electrons.
- **Central Barrel and Ion-Endcap Regions**: Utilize a cost-effective, high-granularity Shashlik-style sampling architecture. In these regions, alternating layers of 1.5 mm-thick polystyrene-based plastic scintillator and 0.35 mm-thick lead are stacked to a total depth of approximately 48 cm (≈16 X₀), defining the longitudinal containment and sampling performance. The modular design features projective towers with a front-face cross-section of 4 × 4 cm²; in the barrel section, modules are frustum-shaped to ensure projectivity toward the interaction region, while the ion-endcap uses rectangular prisms [2512.04432].

Each Shashlik module is penetrated by 16 double-clad wavelength-shifting (WLS) fibers (1.2 mm diameter) traversing the entire stack. The rear of the fibers is mirrored for enhanced photon return, and readout is performed at the front face with 6 × 6 mm² silicon photomultipliers (SiPMs).

**Table 1: ECAL Segmentation and Materials**

| Region         | Technology                  | Absorber/Scintillator [thick] | Depth (X₀) |
|----------------|----------------------------|-------------------------------|------------|
| Electron-Endcap| pCsI crystal               | —                             | 20         |
| Barrel         | Shashlik (Pb/scintillator) | 0.35 mm Pb / 1.5 mm plastic   | 16         |
| Ion-Endcap     | Shashlik (Pb/scintillator) | 0.35 mm Pb / 1.5 mm plastic   | 16         |

## 2. Optical Design, Light Collection, and Readout

EicC's Shashlik implementation leverages advanced light-collection and optical-enhancement techniques for maximizing photon yield and uniformity:

- **Wavelength-Shifting Fiber Matrix**: 16 WLS fibers arranged uniformly across each module efficiently capture scintillation photons and provide fine transverse sampling.
- **Fiber Endpoint Treatment**: The rear ends employ high-reflectivity ESR mirror films (>98%), minimizing photon losses.
- **Interlayer Reflectivity Enhancements**: ESR films are inserted between scintillator and lead layers to reflect side-escaping photons back towards fibers. The module's outer surfaces are painted with TiO₂-loaded coatings to further improve internal reflectivity [2512.04432].
- **Mechanical Stability**: Compression rods guarantee uniform layer contact, suppressing optical gaps that could degrade light collection.
- **Photosensor**: SiPMs with a photon detection efficiency (PDE) ≥25% in the WLS emission band are employed, directly coupled at the fiber front ends.

## 3. Performance: Energy and Position Resolution

Extensive Geant4-based simulations were carried out to optimize ECAL performance. For the Shashlik modules in the barrel and ion-endcap, critical metrics include:

- **Energy Resolution**:
  $$
  \frac{\sigma_E}{E} = \frac{5.0\%}{\sqrt{E \ [\mathrm{GeV}]}}\oplus 1.0\%
  $$
  The stochastic term is dominated by the sampling fraction:
  $$
  f_\mathrm{s} = \frac{1.5\,\mathrm{mm}/43\,\mathrm{cm}}{1.5\,\mathrm{mm}/43\,\mathrm{cm} + 0.35\,\mathrm{mm}/0.56\,\mathrm{cm}} \simeq 0.33
  $$
  and photostatistics is typically $N_\mathrm{pe} \sim 30$/MeV, producing a negligible additional $\sim5\%/\sqrt{E}$ term [2512.04432].

- **Position Resolution**:
  $$
  \sigma_x(E) \simeq 5.0\,\mathrm{mm}/\sqrt{E}\oplus 1.0\,\mathrm{mm}
  $$
  Logarithmic weighting reconstruction is used for the hit position, deploying per-tower energy deposits weighted as $w_i = \max\{0, W_0 + \ln(E_i/E_\mathrm{tot})\}$, with $W_0=3.5$ for Shashlik.

- **Energy Linearity**: The fractional non-linearity remains within ±1% across the 0.1–15 GeV operational range.

## 4. Particle Identification and Electron-Pion Discrimination

Shashlik modules achieve high-quality electron/hadron separation by exploiting differences in electromagnetic and hadronic shower profiles and leveraging the precise energy-momentum comparison (E/p):

- **Separation Variables**: The $E/p$ ratio, spatial shower dispersion $D = \sqrt{D_x^2 + D_y^2}$, and cluster profile shape are used for PID cuts.
- **Simulated PID performance at 2 GeV/c**:
  - Electron efficiency: $\varepsilon_e \approx 99.3\%$
  - Pion misidentification: $\varepsilon_{\pi \rightarrow e} \approx 0.7\%$
  - Pion rejection factor: $\sim 100:1$ for $>99\%$ electron retention [2512.04432].

The electron/pion discrimination performance is robust due to intrinsic fine sampling and precise spatial resolution from the modular geometry.

## 5. Calibration, Uniformity, and Operational Considerations

EicC ECAL design addresses calibration and uniformity via:

- **Module Calibration**: Equalization based on minimum-ionizing particle (MIP) responses, with position-dependent corrections for fiber attenuation.
- **Temperature Compensation**: SiPM bias voltage is adjusted to correct for thermal drifts, as system performance can be sensitive to $+45$ mV/°C at the SiPM [2002.07709].
- **Longitudinal Segmentation**: Each WLS fiber is read out independently at the module front, enabling flexibility in introducing fine longitudinal sampling or potential PID via shower profile discrimination.
- **Channel Uniformity**: Simulated and prototyped systems achieve module-to-module response variations $\lesssim2\%$ after calibration [1812.00672].

## 6. Comparison to Shashlik Calorimetry in Other Facilities

The EicC Shashlik ECAL design parameters benchmark favorably against other modern shashlik implementations:

| Facility/Prototype            | Stochastic Term [%/√E] | Constant Term [%] | Granularity      | Reference         |
|-------------------------------|------------------------|-------------------|------------------|-------------------|
| EicC Barrel / Ion-Endcap      | 5.0                    | 1.0               | 4 × 4 cm²        | [2512.04432]      |
| MPD/NICA Barrel               | 3.0                    | 2.4               | 5–6 cm towers    | [2002.07709]      |
| ENUBET/Ultra-Compact Module   | 15.7                   | <1                | 3 × 3 cm²        | [1812.00672]      |
| DarkQuest (ex-PHENIX)         | 13.5                   | 2.1               | 5.25 × 5.25 cm²  | [2502.20590]      |

EicC achieves improved energy and position resolutions via finer sampling (thin Pb/scintillator layers), optimized WLS fiber coverage, and high-reflectivity interfacial treatments. The modular approach facilitates scalability and maintainability essential for a large-scale collider environment.

## 7. Future Directions and Advanced Concepts

The EicC calorimeter R&D continues to explore enhancements in timing, radiation hardness, and deep longitudinal segmentation. Notable global trends in shashlik calorimeter evolution include:

- **Radiation-Hard Scintillator Media**: Deployment of LYSO:Ce, LuAG ceramics, or polysiloxane-based scintillators for harsh radiation environments [2203.06731, 2001.03130].
- **Wavelength-Shifting Fiber Technology**: Optimization of fiber diameter, cladding, readout interface, and reflective terminations to improve light yield and response uniformity.
- **Ultra-Fine Sampling Structures**: GRAiNITA-style micro-shashlik concepts offer $\sim$2–3%/√E stochastic terms and $\sim$1% constant term, with extremely fine absorber/scintillator mixing [2312.07365].
- **Integration of Deep Learning Algorithms**: Adoption of CNNs for position and cluster reconstruction has demonstrated $\sim$30% spatial resolution improvement over CoG methods in Tsinghua/MPD ECal tests [1902.03629].
- **Timing Capabilities**: Integration of capillary/quartz fiber readout enables $\mathcal{O}(50)$ ps timing for EM showers, addressing pile-up and event separation at high-luminosity colliders [2303.05580, 2205.02500].

Ongoing studies involve full detector integration, high-rate operation, radiation damage mitigation, and large-scale calibration protocols.

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The EicC electromagnetic calorimeter system exemplifies state-of-the-art shashlik technology, balancing energy and position resolution, granularity, and scalability to meet demanding collider physics requirements [2512.04432]. Its architecture and optimization strategy are consistent with, and in certain respects surpass, the capabilities of analogous contemporary sampling calorimeters in high-energy and nuclear physics.

Source: https://www.emergentmind.com/topics/electron-ion-collider-in-china-eicc