Molecular Dynamics Simulations of Bubble Nucleation in a Liquid Scintillator

The Scintillating Bubble Chamber is a detector experiment searching for Weakly Interacting Massive Particles, with estimated sensitivities as low as 100 eV. Its use of a liquid scintillator causes electron events to deposit most of their energy electronically, rather than into nuclear recoils, which contributes to this low sensitivity. However, existing molecular dynamics simulations of bubble formation do not incorporate the energy losses to photons or time-delayed releases that occur in liquid argon. In this study, we use the HOOMD-blue molecular dynamics framework to simulate an idealized model of electron events in liquid argon, including energy deposited via photon creation, ionization, and direct nuclear recoils. A multi-stage bubble growth process similar to that reported in the literature was observed. When comparing simulated thresholds under this model to those under the standard Seitz ``heat spike" model, we found that scintillation raises the average energy required to form a bubble by a factor of 2.16. This indicates that more energy is lost than is accounted for by photon creation and that thermal energy deposited after the bubble's rapid growth phase does not contribute to nucleation. This conclusion was further strengthened by simulations showing increased thresholds with slower scintillation processes, even at identical thermodynamic conditions.