Design and Mechanical Integration of Scintillation Modules for SUB-Millicharge ExperimenT (SUBMET)

We present a detailed description of the detector design for the SUB-Millicharge ExperimenT (SUBMET), developed to search for millicharged particles. The experiment probes a largely unexplored region of the charge-mass parameter space, focusing on particles with mass $m_{\chi }<1.6\text{ GeV}\mathrm{/}{c}^2$ and electric charge $Q<{10}^{-3}e$. The detector has been optimized to achieve high sensitivity to interactions of such particles while maintaining effective discrimination against background events. We provide a comprehensive overview of the key detector components, including scintillation modules, photomultiplier tubes, and the mechanical support structure.