Speaker
Description
Optical time projection chambers (OTPCs) with gaseous electron multiplier (GEM) amplification are well suited for applications requiring fine spatial granularity for particle track reconstruction. OTPCs reconstruct tracks by measuring scintillation light produced in the electron avalanche, often assuming that the observed light faithfully reproduces the spatial distribution of charge emerging from the GEM(s). Comparisons between simulations and measurements, however, have shown that observed particle tracks can be systematically brighter and broader than predicted using this assumption. In this talk, we present laboratory measurements of multiple GEMs demonstrating that light produced within a GEM hole can propagate through the GEM substrate and emerge from neighboring holes, producing optical broadening. We then present Geant4 optical-transport simulations that reproduce these measurements, validating the modeling of light transport through the GEM. Using avalanche-light distributions derived from Garfield++, we simulate realistic GEM optical effects in full detector geometries, including reflections from surrounding detector surfaces. These simulations are used to construct position-dependent multi-hole point-spread functions across the imaging plane. We also develop deconvolution methods that correct for GEM-induced optical broadening in reconstructed particle tracks.