TROPix: A parametric tool reproducing the output of the HEPD-02 pixel detector

This paper introduces TROPix, a parametric simulation tool designed to reproduce the output of silicon pixel detectors. Developed for the Direction Detector of the HEPD-02 detector on the second China Seismo-Electromagnetic Satellite (CSES-02), TROPix utilizes the GEANT4 toolkit for energy deposition and a parametric approach for charge generation and diffusion. The simulation process incorporates thermal noise and digitization, with all parameters fine-tuned using experimental beam-test data. Although TROPix is tuned for HEPD-02 data, it can also be adapted for use with other detectors employing pixel sensors, providing a versatile and computationally efficient solution for numerous applications. Results for Monolithic Active Pixel Sensors (MAPS) based on ALTAI chips are presented, highlighting TROPix's ability to replicate the property of pixel clusters, defined as the number of pixels fired by the particle passage. These characteristics comprehend the dependencies on charged particle deposited energy and incident angle, as well as the typical shapes of clusters. Validation using beam test data acquired with ALTAI sensors demonstrates that TROPix reproduces the cluster size dependence on deposited energy, with agreement within 20%. For cluster shape occurrences, the simulated results align with the data within 25% of the total uncertainty.