Bubble growth dynamics for C3F8 bubble chambers

Abstract

PICO is a direct dark matter search experiment that utilizes bubble chambers and the acoustics of growing bubbles to discriminate signal from background events [5]. It has been shown that temperature perturbations from equilibrium significantly affect the growth of a bubble in superheated water [17], particularly in the form of an onset delay to perceptible growth. In this thesis the temperature perturbation method is applied to superheated C3F8 to describe the acoustic background discrimination achieved by the PICO experiment. We reproduced the delay in water and confirmed its occurrence in C3F8. We hypothesized that the delay can be used for optical background discrimination. However, it was shown that the model does not apply to the energy deposition of different types of particles as all of them, e.g. incoming alpha particles and neutron induced nuclear recoils, create multiple bubbles along their tracks. Those bubbles, in the end, coalesce to form the observed single visible bubble.