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Direction measurement of weakly interacting massive particles in time-projection chambers can provide definite evidence of their existence and help to determine their properties. This article demonstrates several concepts for charge amplification in time-projection chambers that can be used in direction-sensitive dark matter search experiments. We demonstrate reconstruction of the "head-tail"effect for nuclear recoils above 100 keV, and discuss the detector performance in the context of dark matter detection and scaling to large detector volumes.

This paper presents a measurement of the ratio of photon to electron production and the scintillation spectrum in a popular gas for time projection chambers, carbon tetrafluoride (CF 4 ), over the range of 200 to 800 nm; the ratio is measured to be 0.34±0.04. This result is of particular importance for a new generation of dark matter time projection chambers with directional sensitivity which use CF4 as a fill gas.

Directional detection of dark matter can provide unambiguous observation of dark matter interactions even in the presence of background. This article presents an experimental method to measure the direction tag ("head-tail") of the dark matter wind by detecting the scintillation light created by the elastic nuclear recoils in the scattering of dark matter particles with the detector material. The technique is demonstrated by tagging the direction of the nuclear recoils created in the scattering of low-energy neutrons with CF 4 in a low-pressure time-projection chamber that is developed by the DMTPC collaboration. The measurement of the decreasing ionization rate along the recoil trajectory provides the direction tag of the incoming neutrons, and proves that the "head-tail" effect can be observed.

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