Speaker
Description
The PICO experiment uses bubble chambers filled with superheated C$_3$F$_8$ for spin-dependent WIMP dark matter searches. One of the main sources of background in these detectors is alpha particles from decays of environmental $^{222}\mathrm{Rn}$, which nucleate bubbles that are visually indistinguishable from WIMP candidate events. It was previously determined that alpha-induced bubbles can be discriminated against acoustically, based on the signal from alpha events being consistently larger in magnitude than from nuclear recoil/WIMP-like events. By studying the dynamics of bubbles nucleated by these two types of ionizing radiation from the first stages of their growth, we develop a physical model for the acoustic discrimination for the first time. This model is verified by comparing the simulated and the experimental distributions of acoustic energies radiated during bubble expansion.
