A REST-based Monte Carlo Simulation and Data Analysis Framework for the N$\nu$DEx Experiment

The N$\nu$DEx experiment is designed to search for neutrinoless double-beta decay ($0\nu \beta \beta$) of ${}^{82}\mathrm{S}\mathrm{e}$ and is planned to be deployed at the China Jinping Underground Laboratory (CJPL). It employs a high-pressure time projection chamber (TPC) filled with ${}^{82}\mathrm{S}\mathrm{e}{\mathrm{F}}_6$ gas and a Topmetal pixelated charge readout system. The high $Q_{\beta \beta }$ value of ${}^{82}\mathrm{S}\mathrm{e}$, together with the track reconstruction capability of a gaseous TPC, provides strong potential for background suppression. In this work, we develop a full simulation and reconstruction framework for the N$\nu$DEx experiment based on the REST (Rare Event Searches Toolkit) software framework. To meet the detector-specific requirements of N$\nu$DEx, customized simulation processes are implemented to describe the detector geometry, electron drift and diffusion, the Topmetal readout plane, signal formation, and electronics response. These developments enable a complete software description of the detector response from energy deposition to digitized waveforms. A waveform-fitting-based reconstruction method is further applied to the simulated signals to extract the deposited charge and reconstruct the event energy. For simulated signal events, the reconstructed energy resolution reaches a full width at half maximum (FWHM) of less than 1%, satisfying the design requirement of the experiment. The resulting simulation and reconstruction chain provides a basis for future studies of detector response, background rejection, event classification, and optimization of the N$\nu$DEx detector design.