Dark Matter Particles May Have Been Detected 156
During two seminars at Stanford and Fermilab on Thursday, researchers described signals for two events detected deep in an old iron mine in Minnesota that might mark the first detection of dark matter — or not. The presenters said the chances that the signals they detected were caused by something other than "neutralino" dark matter particles was 23 percent. "One source indicates that we'd need less than 10 total detections within the CDMS' range in order to have a high degree of confidence in the results." The NY Times describes the Cryogenic Dark Matter Search methodology: "The cryogenic experiment is nearly half a mile underground in an old iron mine in Soudan, Minn., to shield it from cosmic rays. It consists of a stack of germanium and silicon detectors, cooled to one-hundredth of a degree Kelvin. When a particle hits one of the detectors, it produces an electrical charge and deposits a small bit of energy in the form of heat, each of which are independently measured. By comparing the amounts of charge and heat left behind, the collaboration’s physicists can tell so-called wimps from more mundane particles like neutrons, which are expected to flood the underground chamber from radioactivity in the rocks around it." Here are the research team's summary notes of the latest results (PDF).
Re:It's the lack of energy, stupid! (Score:5, Interesting)
So by reducing the temperature of the sensor to half a degree Kelvin, they have reduced the energy level of the sensor to almost nothing. Yes, it interacts with incoming particles, but it also radiates gravitational waves that could be misinterpreted as external particles. In essence, the detector is detecting itself.
Of course, there is a 23% chance I am completely wrong.
There's a 100% chance you're wrong. Gravitational waves can't be absorbed by these detectors in any meaningful way. To notice the effects of even massive gravitational waves you need a huge detector (like LIGO [wikipedia.org]). Also, gravitational waves happen when a gravitational field changes. They propagate this change through the universe. Objects at rest aren't emitting gravitational waves.
If you isolated these sensors from the universe and let them sit for a long time, they wouldn't lose their mass to gravitational radiation - they'd probably sit around until death by baryon decay in 10^33 years.
And no, they're not detecting baryon decay either.
Supersymmetry lives? (Score:3, Interesting)
If they have really found neutralinos [wikipedia.org] then wouldn't that would mean supersymmetry is confirmed? It that case it is a whole new ballgame in particle physics. There are blogs out there that are saying that CERN is about to announce something big too.
Re:Paper pre-print to appear on arxiv (Score:2, Interesting)
Pentaquarks went away after 50 events were discovered at more than 10 different labs...
The difference between pentaquarks and this experiment is that CDMS did their analysis blind. That is, they agreed on what a positive signal would look like before they looked at the data. There's much less chance of making a stupid systematic error when you do a blinded analysis. The pentaquark folk went wrong when they did hundreds of cuts on previously gathered data trying to find anomalies. When you look at a bunch of data and pick out blips, the chance that they're random fluctuations instead of real signal is high.
No longer dark? (Score:3, Interesting)
If we can detect it, does that mean we have to stop calling it dark matter?
Re:It's the lack of energy, stupid! (Score:3, Interesting)
I believe you're talking about different things - the detector itself vs dark matter.
Lets do some armchair physics, since I need to dumb it down to my level anyway (I've got a minor in physics...). The known factors of (theoretical) dark matter is it has gravity but does not emit or reflect energy as heat or light, and the reason we think it exists is because galaxies aren't spiraling apart fast enough given the amount of visible matter. I won't pretend to understand that, I'll take it as a given and that the real physicists know what they're talking about.
Now imagine you put up a "wall" and throw particles at it. When a visible particle hits the wall, it bounces off and release some energy such as heat, just like when you toss a ball at the garage door - it may not be much, but it certainly is there. Now say we throw a dark matter particle at that same wall - what form of energy would it release, assuming it doesn't retain all energy (perfect reflection)? Personally, I don't know, but gravity doesn't sound like a bad suggestion.