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.

By: Ryan

Ryan — Wed, 23 Apr 2008 15:12:51 +0000

Shouldn’t physicists trying to prove the existence of dark matter be attempting to make it in a laboratory, or capture it? It seems that even if these “detections” succeeded, even the three part experimental result Mr. Cole described, it still falls short of satisfactory proof. Why aren’t dark matter researchers attempting to produce the stuff in laboratories? Figure out the physical process that produces this stuff and replicate it. Or, gather some up from the space around Earth. If 90%+ of the mass of the universe is this dark matter then there has to be some in the space around Earth. Get a spoon and collect some. The experimenters here said they were measuring the impact of Earth on cloud of dark matter. Why not measure the cloud directly? Prod it with a thermometer, shine light on it.

There is not one drop of experimental evidence that this dark matter stuff is real. While it is true that Kepler’s laws don’t predict the motion of a spiral galaxy, it is a totally invalid conclusion to presume Kepler’s laws are right and the universe is wrong. It’s saying that instead of Kepler’s laws not applying to galaxies (we had no good reason to ever think they would), the laws of radiation and light do not apply to galaxies, that we can’t trust our lying eyes. To say it’s not the model that’s wrong but rather the universe is arrogant, myopic and unscientific. It betrays dogmatism and lacks creativity.

If this dark matter stuff were real people would be trying to prove its existence by creating it or gathering it. Folks, just keep in mind there may not be such a thing as dark matter and energy, antimatter emitting black holes and neutron stars the size of solar systems. We’ve been looking for evidence of those things for decades now and not found one scrap of it. We’ve had to modify the heck out of the original theories to stop them from making incorrect predictions and at some point in the life of a hypothesis, when you’ve tested it so many times, and all it does is fail, and you modify away the failure, test again and it fails again; eventually you should start over with a fresh theory.

Some cosmology theories make successful predictions.

http://www.holoscience.com/news.php?article=66b0jzyh

By: jls

jls — Wed, 23 Apr 2008 03:05:13 +0000

Thanks a lot for writing this guest post. It was clear and useful.

By: Dark Matter Detected? « Where We Make Our Stand

Dark Matter Detected? « Where We Make Our Stand — Tue, 22 Apr 2008 23:58:49 +0000

[...] I posted this before Phil updated his post with a link to Cosmic Variance that explains why the findings, while interesting, are nowhere near conclusive. We can say with a [...]

By: yet anotherblog | Απευθείας ανίχνευση “σκοτεινών” σωματιδίων;

yet anotherblog | Απευθείας ανίχνευση “σκοτεινών” σωματιδίων; — Tue, 22 Apr 2008 23:20:37 +0000

[...] UPDATE: το προδημοσιευμένο άρθρο στο arxiv εδώ. Σκληρή κριτική από τον Juan Collar στο Cosmic Variance εδώ. [...]

By: Adam

Adam — Tue, 22 Apr 2008 17:31:44 +0000

Then again, there are plans for dark matter detectors on the International Space Station - not the moon, but definitely out there.

By: Sean

Sean — Tue, 22 Apr 2008 15:08:37 +0000

Pop, dark matter definitely clumps — there is more of it in galaxies than outside galaxies, for example. The precise amount of clumping is still unclear. But that would still be consistent with a seasonal variation; whatever the clumping is, there is still an average velocity for dark matter within the solar neighborhood.

Brian, doing the experiment on the Moon would undoubtedly eliminate certain possible systematic effects, while eliminating others. It would also be more expensive by several orders of magnitude.

By: Pop

Pop — Tue, 22 Apr 2008 14:51:43 +0000

I’ve read some of the other blogs about this. I have a question. Does DM clump, which implies motion as well? All known matter seems to form in clumps with areas of low density. Or does DM spread itself evenly across the univers? The question is moot since we haven’t proven the existence of DM yet. But, in looking at these data it should be a point of consideration. If DM is uniform and static, seasonal variation will be more easily detected. If DM clumps and is in motion, seasonal variations would be dificult to detect. Determining these data do confirm DM, then it also shows that DM is uniform and static. No?

By: Brian

Brian — Tue, 22 Apr 2008 14:12:08 +0000

If a similar experiment were placed on the Moon or Mars and gathered consistent data, would that help eliminate the argument of seasonal effects?

By: Andi Chapple

Andi Chapple — Tue, 22 Apr 2008 13:59:27 +0000

hi -

interesting post, interesting other posts linked to from the editorial bit, thanks all round. I’m not qualified to comment on the science, but I will ask: what is it about physics that makes so many of the professionals so rude to each other in public? I understand (I think) that Juan Collar is worried that this other team have made his job explaining what he’s doing to non-professionals a bit harder, but still, politeness never hurt anyone. it’s only the nature of the universe, for goodness’ sake - it’s not like your children are being starved to death or something.

best wishes,

Andi

By: Blue Collar Scientist » Blog Archive » Dark Matter Directly Detected?

Blue Collar Scientist » Blog Archive » Dark Matter Directly Detected? — Tue, 22 Apr 2008 01:46:16 +0000

[...] But we have some reservations. [...]