Photograph of the inner-most portion of the PandaX-II detector before installation at Shanghai JiaoTong University. A PandaX-II graduate student stands next to the detector to demonstrate the size of the detector component that is responsible for detecting the tiny signals expected from a WIMP interaction with a xenon atom.

U-M physicists Professor Wolfgang Lorenzon and Research Scientist Michael Schubnell are part of the PandaX team who has recently reported the newest constraints on direct detection of Dark Matter. Despite overwhelming indirect evidence for its existence from astrophysical observations, dark matter has not yet been directly observed. Moreover, the standard model of particle physics, which has been very successful in explaining the properties of ordinary matter, can neither explain dark matter’s presence nor its properties. The discovery and identification of dark matter would therefore have a profound impact on cosmology, astronomy, and particle physics.

The measurement from PandaX has reached the best level of sensitivity for directly detecting Dark Matter particles. No evidence was found for the existence of Weakly Interacting Massive Particles (WIMPs), a class of dark matter particles which came into existence shortly after the Big Bang.

The PandaX (Particle and Astrophysical Xenon) detector uses 330 kg of ultra-pure liquefied xenon as the detection medium for Dark Matter. The PandaX experiment is located in the China JinPing Underground Laboratory (CJPL), about 2,400 m below a mountain to shield it from cosmic ray background. This experiment searches for extremely small signals caused by collisions of xenon atoms and billions of dark matter particles flying through it.

The recoiling xenon atoms produce signals which can be recorded by sensitive detectors. The latest result is based on a 100 day measurement with the second generation PandaX-II detector.

“PandaX has not only reached the frontier in dark matter searches, but also surpassed all other experimental efforts in Dark Matter direct detection searches”, said Professor Wolfgang Lorenzon.

Indeed, this result, which has been accepted by Physical Review Letters (PRL) and is available at http://arxiv.org/pdf/1607.07400v2.pdf, represents “the most important publication in the Dark Matter field so far this year”, as exclaimed by one of the PRL referees of the paper.

In the near future, PandaX will continue to lead the search for Dark Matter and continue to push forward into uncharted territory. With 500 kg of xenon detector material, it is the largest running dark matter detector in the world, and has the highest sensitivity for dark matter detection.