Calibration of an Irradiated Prototype for the EIC Zero-Degree Calorimeter

TL;DR

This work evaluates the radiation hardness of a SiPM-on-tile Zero-Degree Calorimeter prototype for the EIC by exposing a 563-channel device to a fluence of $10^{11}$ protons/cm$^2$, simulating one year of nominal luminosity. Despite substantial and nonuniform SiPM damage, the study demonstrates that pedestal and MIP calibrations can be performed on a per-channel basis using cosmic-ray data, with the MIP signal-to-noise ratio remaining above $5$ in all layers. The results validate the feasibility of the ZDC SiPM-on-tile technology for forward calorimetry at the EIC and provide a realistic benchmark for operation and future CALOROC-based readouts. The analysis highlights a layer-dependent dose gradient and identifies nonfunctional channels as areas for further investigation, informing long-term operation strategies and upgrade planning.

Abstract

We study the response of a prototype Zero-Degree Calorimeter (ZDC) detector to irradiation equivalent to 10$^{11}$ 1-MeV protons/cm$^2$, which matches the expected exposure after one year of operation at full nominal luminosity at the future Electron-Ion Collider (EIC). The prototype consists of 563 channels and represents about 10 percent of the final ZDC design in terms of both channel count and detector volume. It was irradiated at the NASA Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory (BNL) with a dose equivalent to 10$^{11}$ protons/cm$^2$. We demonstrate that, despite significant radiation damage to the SiPMs and non-uniform degradation across the detector volume, the detector can be successfully calibrated on a channel-by-channel basis using cosmic-ray data. The damage profile, similar to what is expected in the experiment, varies by an order of magnitude or more across the detector. Even for the most heavily damaged channels, the signal-to-noise ratio for a MIP signal remains above 5. This study provides a realistic test of the system's performance under irradiation. It complements previous SiPM-specific irradiation studies and will inform the future operation of the ZDC and other detectors that use SiPM-on-tile technology.

Figures (8)

• Figure 1: Schematic plot (left) and picture (right) of the ZDC prototype.
• Figure 2: ZDC installed at the beam dump in the NSRL target room.
• Figure 3: Left: A typical pedestal distribution fitted with a Gaussian function before irradiation; Right: A typical MIP ADC spectrum before irradiation.
• Figure 4: Left: Example dark current measurement for a single SiPM (Hamamatsu S14160 1315PS) channel at multiple bias voltages, mapped onto benchmark curves to infer the radiation fluence. Right: Inferred radiation fluence for all SiPM channels in the prototype, showing the variation across layers.
• Figure 5: Designed radiation fluence for the ePIC detector at 1 fb$^{-1}$ integrated luminosity.