Triggering Firmware and T9 Testbeam Efficiency Evaluations for the LDMX Trigger Scintillator*

The Light Dark Matter Experiment (LDMX) is a fixed target, missing momenta/mass experiment aimed at finding dark matter mediated by a heavy dark photon. It is designed with SLAC's 8 GeV electron LCLS-II beam in mind; this beam would pass through a tungsten target and its interactions would be captured in upstream detectors. These upstream detectors have complete angular acceptance, making the experiment sensitive to rare invisible decays as well as decays with low transverse momentum. This talk will focus primarily on one of its subdetectors; the Trigger Scintillator (TS). The device, composed of 3 parallel grids of 48 3x20x3 mm³ scintillating bars, must count up to 5 incoming electrons at a latency of 7 ns. This count will be used with electric calorimeter energy estimates to trigger the LDMX. Demonstrating the TS's high hit efficiency and firmware performance is critical towards demonstrating the viability of the LDMX as a whole; this presentation will cover the studies performed by our collaboration to validate the detector. First, a study was performed in April 2022 at the PS (proton synchrotron) T9 test beam in CERN. A tag and probe hit efficiency metric has been implemented and its performance evaluated against MC (Monte Carlo) and test beam data; this work demonstrates that the hit efficiency of the TS is well understood and greater than 90%. Afterwards we will include our TS reconstruction firmware studies; we have evaluated triggering firmware using a Vitis HLS test-stand and simulated data in preparation for the TS' installation in the beamline at SLAC in summer 2024.