An overview of the imaging layers of the Barrel Imaging Calorimeter for ePIC at the Electron Ion Collider

Barrel Imaging Calorimeter (BIC) is a hybrid detector for the electron-Proton/Ion Collider (ePIC) experiment at the Electron-Ion Collider (EIC). BIC is a high-performance sampling calorimeter with inexpensive, low-power HV-CMOS sensors for shower profiling. The state-of-the-art hybrid concept comprises 6 layers of HV-CMOS sensors interleaved with the first 5 Pb/ScFi layers, followed by a large volume filled with the Pb/ScFi layers. The detector design meets the stringent ECAL requirements in the barrel region as outlined in the EIC yellow report. Some of the important requirements are 10$^4$ $\pi$ suppression at low momenta, decent energy resolution for photon energy reconstruction, fine granularity for good $\pi^0-\gamma$ separation up to 10 GeV, and the measurement of low-energy photons down to 100 MeV with a range exceeding 10 GeV. This report presents an overview of the Barrel Imaging Calorimeter design, with a focus on the imaging layers. BIC with the coverage of (-1.71 $< \eta <$ 1.31), consists of 48 trapezoidal sectors built of layers of scintillating fibers embedded in lead and 6 slots for imaging layers. The imaging layers are composed of AstroPix, an HV-CMOS monolithic silicon sensor inspired by ATLASPix3 and MuPix, designed using a 180 nm CMOS process for future gamma-ray astrophysics missions. The imaging layers consist of Trays holding the AstroPix Staves that are built out of Modules. BIC will incorporate a total of 140 m$^2$ of AstroPix sensor area in the barrel imaging region. The AstroPix sensors offer the advantages of a fully monolithic structure, low manufacturing cost, and a low material budget, along with fast charge collection, high radiation tolerance, and low-power operation. They feature large sensitive areas, low noise, a wide dynamic range, and good energy/spatial resolution. The report will include a brief discussion on AstroPix performance.