Development of readout electronics for the electromagnetic calorimeter in the DarkShine Experiment

The DarkShine experiment detects dark photons by measuring the energy loss of a single electron after scattering. Its electromagnetic calorimeter is primarily responsible for accurately reconstructing the energy of the recoil electrons and bremsstrahlung photons. The performance of the electromagnetic calorimeter is crucial, as its energy measurement precision directly determines the sensitivity to dark photons. The DarkShine electromagnetic calorimeter uses LYSO crystals to form a fully absorptive electromagnetic calorimeter. It utilizes SiPMs to detect scintillation light in the crystals, and its readout electronics system deduces the deposited energy in the crystals by measuring the number of photoelectric signals generated by the SiPMs. The DarkShine electromagnetic calorimeter operates at an event rate of 10 MHz, detecting energies ranging from MeV to GeV. These aspects pose challenges to the readout electronics. To meet the requirements of high energy measurement precision, a high event rate, and a large dynamic range, we have researched and designed a readout electronics system based on dual-channel highspeed ADCs. The front-end amplification section of this system uses low-noise trans-impedance amplifiers to achieve high-precision waveform amplification. It successfully achieves a dynamic range of up to a thousandfold through a double-gain readout scheme. The digital section uses 1 GSPS high-speed ADCs to achieve non-dead-time, high-precision waveform digitization. We have completed the design and evaluation test of the readout electronics prototype. Test results show a signal-to-noise ratio greater than 66 dBFS and an ENOB greater than 10.6 bits. Energy spectra measurements have been conducted using LYSO crystals and SiPMs, and an energy resolution of $5.96 \%$ at the 2.6 MeV gamma peak of Th-232 has been achieved.