Geant4-based Optical Photon Distribution Modeling in a Segmented Silicon-Photomultiplier Scintillator Detector for the Recoil Filter Detector Optimization

<span class="sf">Geant4</span> simulations were performed to investigate the scintillation light distribution in a segmented Silicon-Photomultiplier (SiPM) based detector module, which is currently being developed for the upgraded Recoil Filter Detector (RFD). The goal is to replace conventional photomultiplier tubes (PMTs), whose performance degrades under high secondary electron rates, with SiPM arrays coupled to ultra-thin plastic scintillators. Two scintillator types (EJ-228 and EJ-214) and a \(4\times 4\) SiPM matrix were modeled, including detailed optical properties and interface definitions. Simulations of 20 keV secondary electron bunches show that for scintillator thicknesses up to about 25 \(\mu \)m, the generated light remains highly localized and is collected almost entirely by a single SiPM cell. The results show that the expected improvement in counting capability is possible thanks to detector segmentation, and provide guidance for the optimal design of future RFD modules. Abstract Published by the Jagiellonian University 2026 authors