Simulating Scintillator Detectors in the Light Dark Matter eXperiment

The Light Dark Matter eXperiment is a planned fixed-target electron beam experiment with unique sensitivity to sub-GeV dark matter using a missing momentum search. The Trigger Scintillator (TS) subsystem counts the number of electrons per bunch incident on the target, providing crucial information to the missing momentum trigger. The TS is composed of scintillators that emit photons when ionizing radiation passes through them, which are then read out by silicon photomultipliers (SiPMs). A key constraint is that the SiPM board and other TS readout electronics must be separated from the beam. Lengthening the scintillators would achieve this, but would also increase off-beam backgrounds. To assess the impact on signal efficiency of addressing this problem through different designs, such as the inclusion of acrylic light guides between the scintillators and SiPMs, we developed a detailed ray tracing simulation of the TS. This simulation takes a modular approach that enables it to quantify the impact of imperfections, determining the efficiency of detection of the emitted photons for each design. We found that the use of 2x2 mm light guides decreases the efficiency by less than 4%, thus minimally impacting the TS's ability to count electrons while reducing off-beam backgrounds.