Speaker
Description
Dark matter is expected to constitute a large fraction of the universe and may interact with terrestrial detectors through a variety of channels. The PICO collaboration searches for these interactions using bubble chamber technology, which offers two key advantages: intrinsic insensitivity to gamma- and electron-induced recoils, and flexibility in the choice of active fluid. PICO's use of fluorinated targets provides leading sensitivity to spin-dependent dark matter–nucleon couplings.
Building on the currently operating PICO-40L, the next-generation PICO-500 is projected to deliver world-leading limits on spin-dependent interactions. Because the bubble chamber is blind to electromagnetic backgrounds, its sensitivity is ultimately limited by nuclear recoils from neutrons, making a quantitative understanding of the neutron background essential.
This talk presents a Geant4-based simulation model of PICO-500 developed to characterize these backgrounds. We describe the detector geometry implementation and the treatment of radiogenic and cosmogenic neutron sources, including neutrons from cosmogenic activation of detector and shielding materials. Building on these simulations, we develop a statistical model of the neutron background that propagates material radioassay results into a predicted background budget for the experiment. We conclude with projected sensitivities for PICO-500.