Collaborative Research: Developing new readout methods for dark matter detectors with directional sensitivity

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Cosmological measurements over the past ten years indicate that 23% of the matter in theUniverse is dark matter. The favored candidates for dark matter are massive particles which weakly interact with neutrons and protons. Several experiments are underway to detect dark matter by measuring the total energy a dark matter particle transfers to a nucleus in an elastic collision. The proposal is to build a detector that will measure both the direction and energy of the recoiling nucleus. Since the earth moves through a static halo of dark matter, the ability to determine the apparent direction from which the dark matter arrives gives this scheme a decisive advantage over experiments which simply measure the nuclear recoil energy. Two approaches are proposed. In one scheme (using CF4 gas), the image of the recoil is determined by imaging the photons emitted in the amplification process using a CCD camera. The MIT-BU group has demonstrated this method in a 0.05 liter detector and the proposal is to now construct a 250 l detector capable of making a scientifically competitive measurement. The use of CF4 also gives this scheme unique access to spin dependent interactions between dark matter and neutrons and protons. In the second scheme (using CS2 gas), charges collected on the wires of the amplification system determine the direction of the recoil. This method has been demonstrated by the DRIFT collaboration, which operates detectors in the Boulby Mine, and the proposal is to make a major improvement of the electronics in the DRIFT detectors to make them scientifically competitive. The two approaches complement each other by searching for spin-dependent (CF4) and spin-independent (CS2) interactions.In the area of Broader Impacts, although the proposal is for a dark matter detector, the same system could be used for detection of low energy neutrons and may be valuable for radiography, reactor safety or cargo screening. A key element is the large charge coupled device (CCD) camera and optical system.