05.16.13

Searching for Knowledge, ‘To infinity, and beyond!’

Quest for dark matter takes Office of Science supported research from high in the sky to deep underground.

Click to enlarge photo.Enlarge Photo

A photo of two scientists at a computer terminal.Photo courtesy of SNOLAB

COUPP-60 collaboration members Andrew Sonnenschein and Hugh Lippincott monitoring the filling of the detector at SNOLAB in Ontario, Canada.

Scientists are constantly pressing further for understanding, always aspiring to Buzz Lightyear's motto, "To infinity, and beyond!" That's definitely true for research supported by the Office of Science, especially the search for dark matter.

Dark matter is the elusive stuff that holds great things together. It is responsible for much of the gravitational 'glue' that keeps galaxies and galaxy clusters from falling apart; holding their stars in stately orbits instead of whipping away from one another. In fact, dark matter makes up some 27 percent of the mass-energy of the entire universe, compared to the relatively paltry five percent contribution of ordinary matter (the remaining 70 or so percent is thought to consist of dark energy, but that's another story).

Although scientists have a reasonably good sense of what dark matter does and how much of it is out there, they're still struggling to determine what exactly it's made of. Some current theories point to it being largely composed of "WIMPs," Weakly Interacting Massive Particles. WIMPs would very rarely react with anything, which makes them exceptionally difficult to discover. However, their interactions with one another or particles of ordinary matter may occasionally give off detectable signals, and that's what scientists are hoping to see.

Click to enlarge photo.Enlarge Photo

An image of a bubble in a COUPP-60 detector.Photo courtesy of SNOLAB

Image of one of the first bubbles seen in the COUPP-60 detector, located a mile and a half underground at SNOLAB in Ontario, Canada. The bubble appears as a black semi-circle on the lower left-hand side of the image. The white ovals in the center are reflections of LED lights.

That search took researchers into space two years ago, when the Space Shuttle Endeavour lofted the Alpha Magnetic Spectrometer (AMS) experiment to the International Space Station. The AMS experiment, which is supported in the U.S. by the Office of Science, is a particle detector, and one of its missions is to pick up potential signals from these WIMPs. In initial results announced last month, AMS researchers announced the measurement of a feature consistent with originating from WIMPs, but not one that is a smoking gun for dark matter (see http://science.energy.gov/news/in-focus/2013/04-15-13/). Additional data over the coming years is expected to show whether what AMS is seeing comes from dark matter, or something else.

More recently, other Office of Science supported researchers have gone down, deep underground, in the search. Specifically, a collaboration of scientists, including those from Fermi National Accelerator Laboratory (Fermilab) and Pacific Northwest National Laboratory recently started the COUPP-60 (Chicagoland Observatory for Underground Particle Physics) experiment, which is located in the Vale Creighton Mine, a mile-and-a-half below the surface of Ontario, Canada.

Fermilab managed the assembly and installation of the COUPP-60 experiment, which is part of a group of dark-matter experiments in the SNOLAB science observatory. COUPP-60 stands out, since it searches for signs of dark matter via snaps, crackles and pops. It consists of a massive jar, which looks a bit like an oversized test tube, filled with a mixture of purified water and a chemical used in fire extinguishers (CF3I, or trifluoroidomethane). That clear liquid is heated and pressurized almost but not quite to boiling, needing just a bit of extra energy to bubble and broil. The bubbles that appear are signs that energetic particles have passed through, with particles of regular matter leaving a frothy trail, and those of dark matter a singular pop.

Will a dark matter discovery bubble up from the darkness surrounding COUPP-60, or speed in to the AMS experiment in space? It's too soon to tell. But it's certain that Office of Science supported researchers will continue to take their search for scientific understanding to infinity, and beyond!

The Department's Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information please visit http://science.energy.gov/about. For more information about Fermilab, please go to http://www.fnal.gov/External link.

Charles Rousseaux is a Senior Writer in the Office of Science.

Last modified: 6/7/2013 11:50:44 AM