Search for Dark Matter with PICO

PICO是一个由来自加拿大、美国、墨西哥、西班牙、印度和捷克共和国的科学家和工程师组成的国际合作项目。加拿大是这个项目的领导者，该项目旨在利用位于加拿大SNOLAB天体粒子物理设施地下深处的复杂气泡室来寻找暗物质。几十年来，科学家们已经知道，宇宙中近85%的物质以一种从未在地球上直接观察到的形式存在。这种物质被认为在整个星系中无处不在，但与正常物质的相互作用很少，以至于迄今为止从未被观察到。气泡室中含有一种处于亚稳态过热状态的流体，当极少量的能量沉积在气泡室中时，这种流体就会开始沸腾。如果一个暗物质粒子在敏感体积内散射，反冲的原子核将触发一个很容易观察到的相变。PICO用一组快速摄像机观察气泡的形成，由于成核伴随着小的声音爆发，探测器周围有灵敏的压电传感器。所有暗物质探测器的祸根是存在由自然放射性产生的信号，这些信号可以模仿暗物质信号。PICO对光子、电子、α粒子和中子具有出色的本底抑制能力，这在世界上是独一无二的。该实验位于地下深处，以避开地球表面普遍存在的宇宙射线。

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.