Alpha Spectroscopy in a Superheated Bubble Chamber and the Design of the PICO-500 Hydraulic Control Cart

Abstract

Dark matter remains one of the most enigmatic phenomena in astroparticle physics, with compelling evidence for its existence despite a lack of explanation within the Standard Model. Even more puzzling is that it has thus far eluded direct detection via any known interaction mechanism. Weakly interacting massive particles (WIMPs) are a leading dark matter candidate, and the PICO collaboration has made significant strides in searching for WIMPs, focusing on the spin-dependent WIMP-proton interaction. The PICO collaboration employs acoustic energy discrimination to distinguish alpha and neutron-induced background events. The acoustic data is processed into a quantity called the Acoustic Parameter (AP), which is critical for vetoing background events in dark matter searches. This study used background data from the PICO-40L bubble chamber to perform spectroscopic alpha decay analysis. The analysis results showed an improvement in the resolution of the AP and set upper limits on alpha decay rates from the Uranium and Thorium decay series in PICO-40L. Furthermore, the design of the PICO-500 hydraulic control cart has progressed from early concepts to a sophisticated CAD model, with construction set to begin at Queen’s University. With PICO-500 poised to probe unexplored WIMP interaction parameter space, projections indicate it will achieve energy thresholds an order of magnitude lower than those of PICO-40L, bringing the astrophysical community closer to a potential dark matter discovery. The exciting progress of next-generation detectors sets the stage for an impending breakthrough in astroparticle physics.