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APS Physics: Viewpoint — Dark Matter Still at Large

SMU physicist Jodi Cooley, an associate professor in the Department of Physics, writes in the latest issue of Physical Review Letters about hunt by physicists worldwide for dark matter — the most elusive and abundant matter in our Universe.

“No dark matter particles have been observed by two of the world’s most sensitive direct-detection experiments, casting doubt on a favored dark matter model.” — Jodi Cooley

SMU physicist Jodi Cooley, an associate professor in the Department of Physics, writes in the latest issue of Physical Review Letters about the hunt by physicists worldwide for dark matter — the most elusive and abundant matter in our Universe.

Cooley is an expert in dark matter and a lead researcher on one of the key dark matter experiments in the world.

Cooley’s APS Physics article, “Viewpoint: Dark Matter Still at Large,” published Jan. 11, 2017.

The journal is that of the American Physical Society, a non-profit membership organization advancing knowledge of physics through its research journals, scientific meetings, education, outreach, advocacy and international activities. APS represents more than 53,000 members, including physicists in academia, national laboratories and industry in the United States and throughout the world.

Cooley’s current research interest is to improve our understanding of the universe by deciphering the nature of dark matter. The existence of dark matter was first postulated nearly 80 years ago. However, it wasn’t until the last decade that the revolution in precision cosmology revealed conclusively that about a quarter of our universe consisted of dark matter. Cooley and her colleagues operate sophisticated detectors in the Soudan Underground Laboratory in Minnesota. These detectors can distinguish between elusive dark matter particles and background particles that mimic dark matter interactions.

She received a B.S. degree in Applied Mathematics and Physics from the University of Wisconsin in Milwaukee in 1997. She earned her Masters in 2000 and her Ph.D. in 2003 at the University of Wisconsin-Madison for her research searching for neutrinos from diffuse astronomical sources with the AMANDA-II detector. Upon graduation she did postdoctoral studies at both MIT and Stanford University.

Cooley is a Principal Investigator on the SuperCDMS dark matter experiment and a Principal Investigator for the AARM collaboration, which aims to develop integrative tools for underground science. She has won numerous awards for her research including an Early Career Award from the National Science Foundation and the Ralph E. Powe Jr. Faculty Enhancement Award from the Oak Ridge Associated Universities.

She was named December 2012 Woman Physicist of the Month by the American Physical Societies Committee on the Status of Women and earned a 2012 HOPE (Honoring our Professor’s Excellence) by SMU. In 2015 she received the Rotunda Outstanding Professor Award.

Read the full article.


By Jodi Cooley
Southern Methodist University

Over 80 years ago astronomers and astrophysicists began to inventory the amount of matter in the Universe. In doing so, they stumbled into an incredible discovery: the motion of stars within galaxies, and of galaxies within galaxy clusters, could not be explained by the gravitational tug of visible matter alone [1]. So to rectify the situation, they suggested the presence of a large amount of invisible, or “dark,” matter. We now know that dark matter makes up 84% of the matter in the Universe [2], but its composition—the type of particle or particles it’s made from—remains a mystery. Researchers have pursued a myriad of theoretical candidates, but none of these “suspects” have been apprehended. The lack of detection has helped better define the parameters, such as masses and interaction strengths, that could characterize the particles. For the most compelling dark matter candidate, WIMPs, the viable parameter space has recently become smaller with the announcement in September 2016 by the PandaX-II Collaboration [3] and now by the Large Underground Xenon (LUX) Collaboration [4] that a search for the particles has come up empty.

Since physicists don’t know what dark matter is, they need a diverse portfolio of instruments and approaches to detect it. One technique is to try to make dark matter in an accelerator, such as the Large Hadron Collider at CERN, and then to look for its decay products with a particle detector. A second technique is to use instruments such as the Fermi Gamma-ray Space Telescope to observe dark matter interactions in and beyond our Galaxy. This approach is called “indirect detection” because what the telescope actually observes is the particles produced by a collision between dark matter particles. In the same way that forensic scientists rely on physical evidence to reverse-engineer a crime with no witnesses, scientists use the aftermath of these collisions to reconstruct the identities of the initial dark matter particles.

The third technique, and the one used in both the LUX and PandaX-II experiments, is known as “direct detection.” Here, a detector is constructed on Earth with a massive target to increase the odds of an interaction with the dark matter that exists in our Galaxy. In the case of LUX and PandaX-II, the dark matter particles leave behind traces of light that can be detected with sophisticated sensors. This is akin to having placed cameras at the scene of a crime, capturing the culprit in the act.

Read the full article.

By Margaret Allen

Senior research writer, SMU Public Affairs