Modified Thomas-Imel recombination model based on Geant4 simulations

Liquid-xenon time projection chambers (TPCs) are leading the search for dark matter in direct detection experiments. In the active volume of a TPC, interactions between incident particles and xenon atoms yield scintillation photons and ionized electrons, which are used to reconstruct the energy and type of the interaction. Yet these experiments lack a consolidated, fully physics-based model that can characterize their dominant background across their entire energy range of interest. In this talk, I will present a phenomenological modification of the Thomas-Imel model of electron-ion recombination based on GEANT4 track simulations. This new model has a clear physical basis and shows good agreement with data for a much wider energy range than the basic Thomas-Imel model. This model additionally fixes the fluctuation of recombined ions and the dependence on electric field, allowing us to reduce the number of parameters to fit.