DArCSide project at DUSEL

The Depleted ARgon Cryostat for Scintillation and Ionization Detection (DArCSide) collaboration is developing a small-scale (20kg) depleted argon dark matter detector for operation in the Sanford Underground Laboratory at Homestake in 2010. This detector takes advantage of the discovery of underground sources of argon which will be purified for use as Argon-40 in the detector. Successful implementation of this detector will be followed by the development of a multi-ton depleted argon time-projection chamber (TPC) dark matter detector.

Detection of Dark Matter
What is Dark Matter, and how do we detect it? Based upon observations of our Universe, it is believed that the matter that we can see only makes up 5% of the matter in the universe. Based upon the observed speed that things are moving in the universe, and the amount of energy that created the universe, there is a balance problem. Things should be moving slower than they are as we move away from the center of the galaxy.
Picture a figure skater doing a spin on ice, as the skaters hands move away from the body, the spin slows. As the skater pulls her arms in, her rotational speed increases as her mass becomes more centered. As we view our galaxy, the visible mass would indicate that we are a skater with our arms spread out, but our rotational speed would indicate that our arms are pulled in tight. There are two possible explainations for this, one is that the model of gravity that we are currently using is wrong. It may be close, but it is wrong as we cover great distances. The other possible explaination is that although we see a thin figure skater with her arms out, she is actually very wide, but we can not see all of the matter that is making her up.
The unseen matter, or Dark Matter, exists as massive particles that do not interact with normal matter using electrostatic forces. These large particles only interact through the weak nuclear force and gravitational forces. Because of this type of interaction, the particles are extreemly difficult to detect. If dark matter is made of these Weakly Interacting Massive Particles (WIMPs), we can observe them by detecting their collisions with the nuclei on Earth as we intercept their paths around the galaxy.
The DArCSide detector will use Liquid Argon as a medium for WIMP detection due to its efficient conversion of energy from WIMP-induced nuclear recoils into both ionization and scintillation. When a WIMP hits an Argon nucleus, there will be a photon of light emitted. Photo-multiplier tubes around the Argon will detect the small flash of light and record it as a particle detection.
This process is like shooting a bullet at a target. We believe there is a bullet because we hear a sound that isn't explained by any other event other than a gun shot. We can't see the bullet in the air because it is moving so fast and isn't interacting with anything along the way that we can see. We only can detect the bullet when it hits the taget. We still don't see the bullet, but we have evidence based on the hole in the target that something like a bullet has hit it.
There is still a chance that something else made the hole, but our detector is designed to help eliminate other possiblities such as background radiation or cosmic rays. The detector is deep underground to shield it from background radiation and we know how the argon will react to various deep penitrating cosmic particles such as neutrinos.
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