Development of a simulation and analysis framework for NνDEx experiment

Abstract

N$\hat{I}½$DEx aims to search for the neutrinoless double beta decay in ${}^{82}$Se using a high pressure ${}^{82}$SeF${}_6$ gas time projection chamber (TPC). This paper presents a simulation and analysis framework developed specifically for the N$\hat{I}½$DEx experiment. Using density functional theory and two-temperature theory, the reduced mobilities of SeF${}_5^{-}$ and SeF${}_6^{-}$ ions in SeF${}_6$ were calculated, yielding values of 0.444 and 0.430 $\mathrm{c}{\mathrm{m}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ respectively, with an estimated uncertainty within 3\%. The TPC geometry, featuring a cathode, focusing plane, and anode structure, was modeled in COMSOL to compute electric fields. Signal and background events were generated using BxDecay0 and Geant4, while Garfield++ was employed to simulate charge transport and signal induction. Three-dimensional tracks were reconstructed from drift-time differences between the two assumed ion species using a breadth-first search algorithm. To demonstrate the framework's analytical capability, topological variables were taken from reconstructed tracks and used to define selection criteria. A boosted decision tree was then implemented to benchmark the signal-background separation. This simulation framework successfully validates the complete experimental workflow, serving as a robust tool for detector design and future sensitivity studies in the N$\hat{I}½$DEx experiment.