Friday, July 1, 2011

Big bucks better spent elsewhere

"U.S. Dept. of Energy wants billion dollar underground physics lab"


Adrian Cho

June 23rd, 2011


The Large Hadron Collider over in Europe may be making all the physics headlines as of late, but the U.S. Department of Energy is trying to scrape together between one and two billion dollars to build a particle physics lab deep in an abandoned gold mine underneath South Dakota.

If it ever gets built, the Deep Underground Science and Engineering Laboratory (DUSEL) would provide lab and experiment space for particle physicists some 8,000 feet below ground. The depth is important, since all that rock overhead does a bang-up job of intercepting cosmic rays, which are the energetic charged subatomic particles from space that mess with particle physics experiments and (in sufficient concentrations) mutate humans into superheroes.

Scheduled to open in 2020, DUSEL (if it gets funded) would be the home for three flagship experiments:

Long Baseline Neutrino Experiment

Neutrinos are weird little particles. They don't have electrical charge, meaning that they can pass through just about anything, and they're not supposed to have mass, either (but they might).

Scientists now think that neutrinos might be responsible for making sure that we live in a matter universe (as opposed to an antimatter universe), and to test this theory, they're going to send a whole bunch of neutrinos from the world's highest-intensity neutrino beam at Fermilab to DUSEL and watch what happens to them along the way.

Now, Fermilab is in Illinois. DUSEL is in South Dakota. The neutrinos don't care, though: they're perfectly happy to fly between the two, completely ignoring the 600 or 700 miles of rock through which they have to pass. There's no need for wires, tunnels, pipelines, or anything like that, you just point your neutrino beam towards the floor in the direction of South Dakota and off they go.

Neutrinoless Double-Beta Decay Experiment

Radioactivity happens when an element spits out energetic particles in an effort to make itself more stable. This processes is commonly known as decay. In regular double-beta decay, two neutrons in an atomic nucleus turn into protons, firing off a couple electrons along with two neutrinos (or antineutrinos). It's been hypothesized that the same sort of double-beta decay can happen without any neutrinos at all, but this would only be possible if neutrinos are somehow their own antiparticle.

Most antimatter is essentially the same as normal matter except with an opposite charge. Neutrinos, however, are electrically neutral. So what makes an antineutrino different from a neutrino? You'll have to ask your friendly neighborhood physicist on that one (and they probably won't be able to give you a straight answer), but there's a possibility that antineutrinos and neutrinos are the exact same thing, we just haven't figured it out yet.

If we can observe an example of double-beta decay where no neutrinos come out, that means that yes, the neutrino and antineutrino are in fact the same particle. This is apparently revolutionary, and may lead to a measurement of a neutrino's mass. According to the Standard Model of physics, neutrinos aren't supposed to have mass, so this is kind of a big deal.

Dark Matter Search

The universe is made of almost entirely of stuff that we've never see before and know virtually nothing about. Dark energy and dark matter together make up 96% of everything that exists, and they're called "dark" because we have no idea what they are. One theory about dark matter is that it's made up of WIMPs, or weakly interactive massive particles.

Like neutrinos, WIMPs don't have an electrical charge, meaning that they can pass straight through matter without us ever noticing. What they can't pass through are atomic nuclei, but atomic nuclei are small. Very small.

If an atomic nucleus was the size of a golf ball, its electrons would be orbiting over half a mile away. So, the probability of a WIMP smacking into a nucleus is not high. Actually, it's astronomically low. That's pretty much the only hope we have of detecting them, though, so dark matter detectors generally consist of a couple tons worth of atoms just sitting there with all kinds of exquisitely sensitive instruments watching them to see if one single atom moves in such a way that suggests it was plowed into by a WIMP. Isn't science awesome?

No comments: