Friday, May 1, 2015

Dark Matter Detection

Along with the numerous proposed candidates for dark matter, many varying dark matter detection methods have been developed, too. Currently, most of the search is now directed towards weakly interacting massive particles, or WIMPs. The two methods of dark matter detection currently used are very different and as such revolve around completely different facilities, so they will be talked about separately. The most obvious method of proving the existence of dark matter is called direct detection, and it involves finding living WIMPs in a real environment. The other method, indirect detection, instead searches for the particles left behind by a decayed WIMP.

Direct detection generally involves large facilities working in large scales to increase the chance that a stray WIMP will be detected. There are two types of direct detection technologies currently used: cryogenic detectors and noble liquid detectors. Cryogenic detectors operate at temperatures close to absolute zero and are able to detect random particles hitting a crystal absorber by the heat they give off. One of the most famous cryogenic detectors is CDMS, or the Cryogenic Dark Matter Search. Despite the generic name, the program has had 11 possible detections of WIMPs, from 2009 to 2013. The other kind of detection technology, noble liquid detectors, are able to detect particles by the light they produce upon hitting a liquid noble gas, like xenon. Another famous noble liquid detector is LUX, the Large Underground Xenon experiment. LUX is able to detect WIMP collisions with xenon atoms, but also can distinguish neutron collisions with actual WIMP collisions. Both of these detection methods require very isolated facilities far underground to reduce the effect of cosmic rays on experiments.

Indirect detection hinges on the existing theories of supersymmetry and rely on the prior knowledge of a WIMP's construction and degradation. WIMPs should be able to decay into standard model particles, specifically gamma-rays, so many gamma-ray-capable space telescopes search for areas of high gamma-ray concentration. For instance, the Fermi Gamma-ray Space Telescope's discoveries posited that a large amount of gamma-ray radiation from the center of the Milky Way could be because of WIMP annihilation. Another experiment, PAMELA, found an abundance of positrons and cosmic rays, meaning it possibly witnessed WIMP annihilation, too.


CDMSCE @ UC Irvine
Shadow Universe by Corey S. Powell
- Jacob Lee