Dark Matter

DRIFT (Directional Recoil Identification From Tracks)

The DRIFT detector is run by the DRIFT Collaboration (UKDMC, Occidental College, L.A., University of New Mexico) at the Boulby Underground Laboratory in England. It is a gaseous Time Projection Chamber (TPC) that employs Multi-Wire Proportional Chambers (MWPCs) for charge readout. The concept is designed to detect and readout the ionisation produced when a WIMP scatters off a nucleon within a gas molecule and causes a nuclear recoil.

The gas currently used in the DRIFT detectors is carbon disulphide CS₂, which is used for its electronegativity. This means that the CS₂ molecules can easily capture charge and hold on to it so that the ionised molecules are drifted inside the TPC and not just free electrons. Since the CS₂^- ions are more massive than electrons they do not undergo as much diffusion along their path to the readout plane and so the spatial resolution achieved is improved compared with that attainable with drifted electrons.

The DRIFT-I detector ran between 2001 and 2004 at Boulby mine and the knowledge and understanding obtained from the three years of running has been used to improve the design and operational methods employed for the second generation, DRIFT-II detector.

DRIFT-II

DRIFT-IIa has been operational since March 2005 and has obtained a few weeks of unshielded (background) data and a few months of shielded (dark matter) data.

The second generation DRIFT detector is an improved version of the original DRIFT detector. The same basic principle of using a low pressure gaseous TPC in a deep underground laboratory (Boulby) to search for WIMPs is kept. The DRIFT-II detector, however, is an array of DRIFT modules, meaning that the total target mass of the detector is increased with each extra module included.

Each DRIFT-II module has a 1 m³ target (167 g of CS₂) contained within a large stainless steel vacuum vessel. Surrounding the target is a field cage, with a cathode positioned centrally and capped at each end by MWPCs (all stand vertical). The detector modules are surrounded by 40 g/cm² of passive hydrocarbon shielding to suppress neutrons coming from uranium and thorium contamination within the rock walls of the underground laboratory. Modules are then positioned side by side and share the neutron shielding between them.

DRIFT-II Data Analysis

Coming soon ...