Dark matter detected?

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Main Question or Discussion Point

The whole solar system is orbiting the center of the Milky Way at about 250 kilometers per second. But the Earth is also orbiting the Sun. When the Earth is at one part of its orbit, its velocity (30 kps) adds to that of the solar system, but six months later it’s headed the other way, and its velocity subtracts.

If the Earth is slamming into dark matter particles, then we should hit more when the Earth and solar system velocities are in the same direction, and hit fewer when the Earth is moving in the opposite direction of the solar system as a whole six months later. So not only should we see the number of hits go up and down every six months, but that oscillation must line up with the correct dates (June for the former, and December for the latter).

http://www.badastronomy.com/bablog/2008/04/21/dark-matter-detected/
 

Answers and Replies

EL
Science Advisor
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The whole solar system is orbiting the center of the Milky Way at about 250 kilometers per second. But the Earth is also orbiting the Sun. When the Earth is at one part of its orbit, its velocity (30 kps) adds to that of the solar system, but six months later it’s headed the other way, and its velocity subtracts.

If the Earth is slamming into dark matter particles, then we should hit more when the Earth and solar system velocities are in the same direction, and hit fewer when the Earth is moving in the opposite direction of the solar system as a whole six months later. So not only should we see the number of hits go up and down every six months, but that oscillation must line up with the correct dates (June for the former, and December for the latter).

http://www.badastronomy.com/bablog/2008/04/21/dark-matter-detected/
What you are talking about is the DAMA collaboration which has now reconfirmed its own results from a couple of years ago. If I have understood the situation right, they have basically used the same method as in their first experiment, which is unfortunate since this makes it hard to rule out a possible non-dark matter explanation of the anually modulated signal.

Note that, at least for standard dark matter particle models, the DAMA claim has already been ruled out by many other types of direct detection experiments. Hence their results have been greatly disputed in the past, and I'm not sure this experiment will help that much.

A big problem for DAMA is their credibility: They constantly refuse to make their raw data public and by that makes it as good as impossible for others to debug their analysis.
 
Nabeshin
Science Advisor
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What you are talking about is the DAMA collaboration which has now reconfirmed its own results from a couple of years ago. If I have understood the situation right, they have basically used the same method as in their first experiment, which is unfortunate since this makes it hard to rule out a possible non-dark matter explanation of the anually modulated signal.

Note that, at least for standard dark matter particle models, the DAMA claim has already been ruled out by many other types of direct detection experiments. Hence their results have been greatly disputed in the past, and I'm not sure this experiment will help that much.

A big problem for DAMA is their credibility: They constantly refuse to make their raw data public and by that makes it as good as impossible for others to debug their analysis.
Well at any rate, it does sound like they found SOMETHING. Even if people rule out dark matter, I'd be curious to see what it is that they've found.
 
Wallace
Science Advisor
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There's a great opinion piece from someone in the field of DM detection, but not in the DAMA group, over at http://cosmicvariance.com/2008/04/21/guest-post-juan-collar-on-dark-matter-detection/" [Broken].
 
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EL
Science Advisor
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Well at any rate, it does sound like they found SOMETHING. Even if people rule out dark matter, I'd be curious to see what it is that they've found.
I don't think anyone doubted they had really found "something" in their first experiment either. The problem is that this "something" could be "anything". It's not hard to think of possible background components with annual modulation.
I think Wallaces link summarizes the scepticism from the dark matter community pretty well.
 

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