The detectors and the apparatus that surrounds them are located underground
at 2341 ft below the surface (689 feet below sea level), at the Soudan Underground Mine in the Vermilion Range of Minnesota. We will describe the apparatus and the physical components, with an eye towards their purpose to mitigate the backgrounds. We begin by explaining how the experiment is underground to block from space-bound backgrounds. We then describe how the experiment is equipped to place radioactive sources to observe its response to well-known interactions and set the measurement expectations.
The experiment is located underground to use the Earth's crust to block particles coming from space (mostly muons), known as Cosmic Rays, that could directly fake, or produce other particles such as neutrons which could fake a WIMP interaction. While most of this background is mitigated by placing the detector underground, some of the particles from cosmogenic sources do reach the detector, so muons that are not blocked are identified using a Veto system, which tags them and rejects the recorded event. Each detector is enclosed in a hexagonal prism copper housing and the detectors are surrounded by multiple layers of lead and dense plastic (poly) to prevent other types of radioactive sources that produce high energy particles in decays from entering into the detectors. The detector itself is built from a single cylindrical Each detector has a charge and phonon readout system that collects the charge and phonon signals from energy deposits from a particle interaction and turns them into a measurement. The detectors have both charge and phonon sensors, at the top and bottom surfaces, operating at superconducting temperatures, where the signals are collected. Charge electrodes at the top (+2V) and at the bottom (-2V) are the potential source of the electric field in the crystal, and the inter-spaced phonon circuit runs with ground lines (blue rectangles in the figure), creating an additional effect in the electric field near the top/bottom which is designed to help identify interactions which occur near the top and bottom and are known to be poorly measured . The electric field is uniform in the bulk of the detector, while near the surfaces it changes periodically creating an inter-leaved field (also shown in the same figure), thus the response has a vertical-position dependence (labelled the Z-direction). For these reasons the SuperCDMS Soudan detectors are called Interleaved, Z-dependent Ionization and Phonon Detectors or iZips for short.
How does iZIP help detecting dark matter? How does it is different from the HV detectors which also can detect them? Compare the contrast the most important features of both these detectors in the SuperCDMS experiment.
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