Diary of a Seasonal WIMP

Authors note: This was originally the start of a Fast Friday Four, but I know so much about the topic that I just kept writing and explaining things. So enjoy the full post instead.

Photomultiplier tubes try to catch faint flashes of light that indicate a neutrino has interacted with another particle.

The universe is much more than what we can see. In fact, based on the calculated rate of expansion of the universe and the way massive distant objects interact, what we can actually physically see makes up only about 4% of the universe. The rest is split up between dark energy (74%) and dark matter (22%). The former fuels the expansion of the universe while the latter pulls it together through the effect of gravity.

Obviously, not much is known about either because we can’t see it or even detect it. That’s why we call it dark. What these two things are is giant mystery. Some particle physicists, however, believe that dark matter may be a new particle that we have yet to detect. It would be several times more massive than a proton and barely ever interact with regular matter.

Meet the Weakly Interacting Massive Particle, or WIMP for short.

Scientists can, however, tell where the clumps of dark matter exist because its gravity affects the way light filters through space and the way distant galaxies move and interact. As near as we can tell, we’re hurdling through the stuff every second as the Earth spins around the Sun, which in turns spins around the galaxy.

Now, during the winter, the Earth moves in roughly the opposite direction as the Sun with respect to the center of the galaxy. During the summer, it’s moving in the same direction. Thus, in the grand scheme of things, we’re moving faster in the summer than winter. Thus, theoretically, we should got through more of these WIMPSs in the summer than winter.

One experiment, the Italian-run Dark MATter (DAMA) experiment, claims to have seen this seasonal modulation for years. But in science, nothing is sure until it is confirmed over and over. After all, there could be something weird going on with the detector rather than new physics.

So the University of Chicago is jumping into the discussion.

CoGeNT is a massive particle detector buried kilometers below the surface of the earth in the Soudan mine in Minnesota. The Coherent Germanium Neutrino Technology experiment is built to detect the neutrinos that theoretically would be created by normal matter’s interaction with WIMPs. If it can detect certain signals predicted by nuclear theory, then it could prove their existence.

One such theory is the seasonal change in neutrino hits of a specific sort. And it seems like the Minnesota detector is picking up the variation as well. But not to an extent that they can claim a discovery.

To claim discovery, scientists demand a 5 sigma signal, which denotes that there is only a 0.0002% chance that the statistics are creating a fluke discovery. Right now, the Chicago data is only at 2.8 sigma. More data is needed to create a better probability that the discovery is not a fluke.

However, CoGeNT was interrupted in March 2011 by a fire in the Soudan mine. The fire did not directly affect the experiment, but the CoGeNT team has not been able to examine the detector because of clean-up efforts. The detector may no longer work, or if it does work, it may now have different properties.

But since two other experiments have claimed to see signals of this seasonal discrepancy – the aforementioned DAMA as well as Xenon100 – there might actually be something to it. New physics might be just around the corner.

About bigkingken

A science writer dedicated to proving that the Big Ten - or the Committee on Institutional Cooperation, if you will - is more than athletics.
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