Search for Dark Matter with PICO

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PICO is an international collaboration consisting of scientists and engineers from Canada, the USA, Mexico, Spain, India, and the Czech Republic. Canada is a leader on this project which aims to search for Dark Matter using sophisticated Bubble Chambers located deep underground in the Canadian SNOLAB facility for astroparticle physics. Scientists have known for decades that nearly 85% of the matter in the Universe is in a form never directly observed on Earth. This matter is believed to be ubiquitous throughout the galaxy, but has interactions with normal matter so rarely that it has never been observed to date.Bubble Chambers contain a fluid in a metastable superheated state that may begin to boil when the tiniest amount of energy is deposited within the chamber. If a dark matter particle scatters within the sensitive volume, the recoiling nucleus will trigger a phase transition that is readily observable. PICO observes the initial bubble formation with an array of fast cameras, and as the nucleation is accompanied by a small burst of sound, sensitive piezo electric sensors surround the detector. The bane of all dark matter detectors is the presence of signals produced by natural radioactivity that can mimic the dark matter signal. PICO is unique in the world with its excellent background rejection capability for photons, electrons, alpha particles and neutrons, and the experiment is located deep underground to evade the cosmic rays that are prevalent at the surface of the Earth. PICO has the capability of discovering dark matter, or ruling out many of the theories describing its nature. PICO has already set world leading limits on the possible interaction strength, and with the funds provided through this grant, will be able to fully explore the region of parameter space many theories predict for dark matter. With the extended reach of the new detectors that will be operated with funds requested in this application, there is great optimism that a dark matter discovery may be near. The discovery of the nature of dark matter is one of the highest priorities in physics today. The dark matter is known to influence the formation of structures in the Universe and is an important factor in cosmological models. An understanding of dark matter and the way it interacts with normal matter will shape our theories of fundamental particle physics, astrophysics, and cosmology.