Comments on: Guest Post: Juan Collar on Dark Matter Detection

By: GLAST Just Launched! | Cosmic Variance

GLAST Just Launched! | Cosmic Variance — Wed, 11 Jun 2008 16:11:50 +0000

[...] be looking for, a process known as “indirect dark-matter detection,” in contrast to direct detection where a dark-matter particle bumps into an experiment here on [...]

By: Count Iblis

Count Iblis — Sun, 27 Apr 2008 21:28:07 +0000

Why the antagonism, maybe because the result is bad for SUSY…

That’s right. And add to that the fact that most other searches assume DM in the form of WIMPS that will scatter of nuclei and you get some fireworks

By: BDO Adams

BDO Adams — Sun, 27 Apr 2008 20:09:43 +0000

That was a very negative article about a heroic result in astrophysics. 8 sigma!, 3 sigma could
be an artifact, 5 sigma is usually enough to claim a discovery, 8 sigma is some very strong evidence. And the signal phase and modulation, did look like the result the expected from CDM.

Why the antagonism, maybe because the result is bad for SUSY, none of the other experiments
find a significant evidence for CDM, and the combination of the DAMA, CDSII and other experiment
rules out most basic models of neutralino CDM.

By: Dark Matter Detection : Mormon Metaphysics

Dark Matter Detection : Mormon Metaphysics — Sun, 27 Apr 2008 03:05:41 +0000

[...] Nice post at Cosmic Variance about that detection of dark matter in a laboratory. [...]

By: Centauri Dreams » Blog Archive » Dark Matter: Flashes Beneath the Earth

Sat, 26 Apr 2008 17:53:00 +0000

[...] enough to claim a detection of dark matter, or do they merely open up a range of possibilities? Cosmic Variance recently let Juan Collar (University of Chicago), himself a member of a dark matter team, loose on [...]

By: JeffF

JeffF — Fri, 25 Apr 2008 15:37:06 +0000

Brian2,
The diurnal oscillation signature is an interesting one, and not one commonly discussed in the field (because it requires an extremely large data set). DAMA should have time stamps for each particle event so it should be a fairly simple matter to check, though I haven’t checked the numbers to see how significant the signal could be.

By: Brian2

Brian2 — Fri, 25 Apr 2008 03:01:28 +0000

JeffF,
Thanx for the help.
I have been following the results of these laboratory WIMP searches with great interest. I hope DAMA pursues the search for a diurnal oscillation, and I hope they tell us the results whether positive or negative. If they have a discrete record for each recoil, then would it just be a simple matter of resorting the data?

By: JeffF

JeffF — Thu, 24 Apr 2008 14:06:49 +0000

Brian2: It certainly could be that dark matter interacts only gravitationally. In that case these sorts of experiments are hopeless – the rate of scattering in a detector would be far too low. Nonetheless, there is a reasonably powerful argument that dark matter is likely to have weak (W and Z) interactions.

If we suppose the dark matter is composed of some new stable particle X, then this particle should have been pair-produced in large amounts in the hot early universe. As the universe expanded and cooled, however, the X particles stopped being produced and the leftovers annihilated with one another and vanished. It turns out, however, that this annihilation process is imperfect in an expanding universe – if the forces which mediate the annihilation are weak enough, some leftover amount of X particles will remain essentially unchanged until the present day. This is the simplest possible way of explaining how we got our dark matter (though it’s not the only way).

The miracle is that you get roughly the right amount of dark matter if X is a heavy particle whose annihilation is mediated by the W and Z bosons (you’d get much too much if the interactions were gravitational, far too little if they were mediated by photons or gluons). Better yet, most extensions to the Standard Model of particle physics (supersymmetry, extra dimensions, etc.) predict new particles with just these properties, and in many cases the lightest such new particle is stable. It’s not an airtight argument, but it sure seems like cosmology and particle physics may be independently arguing for such a particle: a Weakly Interacting Massive Particle (WIMP), possibly detectable in this sort of experiment (CDMS, XENON, DAMA, COUPP, …)!

By: Brian2

Brian2 — Thu, 24 Apr 2008 02:59:49 +0000

This was an absolutely great article. Thanks, Sean and Juan. I have a question, though.

Do we have any reason to believe that dark matter particles should interact with barionic matter by exchanging W or Z bosons? Maybe they only interact with familiar matter gravitationally. I would very much appreciate an informed response to this question. Thanks in advance to any and all who can help me with this query.

By: ed hessler

ed hessler — Wed, 23 Apr 2008 20:13:19 +0000

I’m not a physicist but my preference is not to make Dr. Juan Collar a regular but to save and use him (as well as others) for informed commentary to help the rest of us understand (a little) what is going on. In addition, such commenters can and often do write longer and more detailed comments on topics that can use focused rays of light.

This was another of your good ideas, Sean and one of the many reasons this is such an interesting and useful blog.

Thanks again.