Decade of Dark Matter

Should we declare this the decade of the WIMPs? Before you answer, let me tell you a bit about WIMPs. Known as Weakly Interacting Massive Particles, they are the leading suspects of what makes up dark matter.  Dark matter comprises 23% of the Universe’s mass, and yet we detect it only by its gravitational pull on visible matter.

Dark matter provided a lively topic of discussion at the recent AAAS Meeting in Boston. Michael Turner, of the University of Chicago’s Kavli Institute for Cosmological Physics, explained it this way at a press conference: “It’s something new. No particle in the standard model can account for it.” And he believes the discovery of the culprit particle is right around the corner; hence the decade of the WIMPs.

As Ryan Wyatt mentioned in his post last month from the AAS Meeting (such similar names, I know), both the Large Hadron Collider (LHC) and the Large Underground Xenon Experiment (LUX) are looking for these particles. In addition, a detector onboard the International Space Station, called the Alpha Magnetic Spectrometer (AMS), has joined the hunt. (Okay, I promise no more acronyms.)

The Alpha Magnetic Spectrometer is the brainchild of Nobel laureate Samuel Ting, who also presented at the press conference. It took Ting 16 years to get AMS into space; it’s now been collecting data for 18 months. And it sounds like they may already have results. Ting was vague, no matter how hard reporters tried to press him, but it sounds like his team plans to publish something in the next few weeks. With the length of time it took to make AMS a reality, Ting says, the results will certainly be worthwhile.

Here’s what he did clarify. AMS has seen 25 billion events—not many for a particle detector like the LHC, but quite a few for a space detector. Almost 8 billion of those are electrons and positrons, and scientists are working around the clock to understand how these interact with one another. Does the ratio between the two change over time? Turner explained that if scientists see a rise followed by dramatic fall, that will indicate a unique source—perhaps dark matter.

So now we must wait for the publication.  And remember, according to Turner’s timeline, we have a whole decade to make discoveries. Ting’s paper could take just a small step toward the description of dark matter. Lisa Randall, a theoretical physicist at Harvard, reminded us that a lot of stuff can mimic dark matter. So it could be a step in the wrong direction. But for her, how models of dark matter fit into these experiments of dark matter is all part of the process. “We’re learning more along the way.”

AMS particle detector: NASA