One of the several dark matter detectors I describe in New Eyes on the Universe is the Large Underground Xenon (LUX) detector. The search for dark matter is much more difficult than the search for the Higgs, but the detectors such as LUX should eventually find WIMP dark matter particles – if such particles exist.
Well, today LUX took a step closer to its goal. For the past two years, scientists have been testing the 3-tonne detector (which contains 350 kg of liquid xenon) in a laboratory. Today, they transferred it to its permanent home 1500m below ground in the old Homestake gold mine – site of the famous Davis solar neutrino experiment. It was a delicate operation: the detector was taken down on air bearings in order to protect it from even minor bumps. But the operation was a success. The detector is in place, and it will start taking data later this year.
The mile or so of rock above the detector will shield it from cosmic rays, but of course dark matter particles will pass through the rock as if it weren’t there. The hope is that once in a while a dark matter particle will collide directly with a xenon nucleus in LUX. When xenon is hit by a particle (it could be a photon, a neutron, or a dark matter particle), liquid xenon both scintillates and ionizes. By using sophisticated detectors that surround the xenon, physicists can measure the ratio of scintillation over ionization energy from the collision. And from that information they can determine the type of particle involved in the collision – whether photon, neutron or dark matter. That’s the hope, anyway. By this time next year we should know more.