Compact VMM3a/SRS integration for high-channel-density TPC readout
The HYDRA (HYpernuclei Decay at R$^3$B Apparatus) TPC is a 5,376-channel pion tracker developed for hypernuclear studies at the R$^3$B experiment at GSI/FAIR. Its installation inside the GLAD dipole magnet imposes strict space constraints above the pad plane. To fit the front-end electronics within this volume, the VMM3a/SRS readout was adapted through a vertical hybrid arrangement and custom boards for signal routing and power distribution. At the same time, the readout had to be integrated with the R$^3$B timing system, which is not natively supported by the SRS. This was achieved by recording the R$^3$B heimtime and trigger signals through spare VMM3a channels, allowing the global timestamps to be reconstructed from the same data stream. Simulations of the PCB coupling indicated low crosstalk between adjacent traces, while S-curve measurements gave a baseline noise level consistent with that reported for the standard VMM3a/SRS readout. Cosmic-muon measurements with the plastic wall provided reconstructed tracks and confirmed event-by-event timing correlation between the two detector systems.