What Are the Pros and Cons of Different WIMP Detection Strategies?

[sysreset]

There has been a spate of writing in the popular media about the debates between scientific teams regarding various WIMP (Weakly Interacting Massive Particle) detection devices in the search for Dark Matter.

(Example: http://www.nytimes.com/2008/04/17/science/space/17dark.html?ref=space from today's New York Times)

I would be curious to hear from knowledgeable people regarding the pros and cons of different WIMP detection strategies, and how they work. For instance, why is it believed that Sodium Iodide, or Liquid Xenon, will emit photons when a WIMP passes through, since WIMPS are not supposed to interact with baryonic matter except via gravitaton?

 

[malawi_glenn]

Maybe this belongs in the subforum "Beyond the standard model" ?

 

[Timo]

For instance, why is it believed that Sodium Iodide, or Liquid Xenon, will emit photons when a WIMP passes through, since WIMPS are not supposed to interact with baryonic matter except via gravitaton?

WIMPS are supposed to have no electric charge and no color charge hence not interacting via electromagnetism or the color interaction. Apart from gravity this still leaves the weak interaction as a mechanism to influence the detector. It's the weak interaction that's supposed to trigger events in these experiments.

I would be curious to hear from knowledgeable people regarding the pros and cons of different WIMP detection strategies, and how they work.

I certainly do not count as "knowledgeable" when it comes to the underground dark matter experiments. My knowledge merely stems on having attended two very interesting talks by a scientist involved in the XENON experiment. Anyways:

A pro is that with the experiments mentioned you scan a different section of the parameter space of the exotic physics models assumed (most notably Supersymmetry) than you do at collider experiments. Collider experiments are limited by the WIMP mass as they need to produce the WIMP (-candidate). Can't remember the main limiting variable for the underground WIMP detections; their mass clearly shouldn't be the problem since they try to detect "naturally occurring" WIMPs.

I personally like the relative simplicity and low-costness (both is just a guess - I doubt they cost even nearly as much as the LHC) of the experiments and the fact that they try to exploit naturally-occuring sources of particles that you have a hard time creating at a lab.

 

[sysreset]

Malawi, okay with me if the thread is moved into a more appropriate forum.

Timi, thank you for responding! Hopefully there are some others out there interested in Dark Matter questions.

Let me rephrase my original question, and please correct my assumptions if they are faulty. I am assuming that WIMPS are the "best" candidate going for the constituants of Dark Matter. I am also assuming there is a valid scientific debate going on about whether WIMPS have been detected or not, using various techniques. I am also assuming that WIMPS can only interact gravitationally with baryonic matter and via the weak interaction, which on a particle level is a much stronger interation than the gravitiational interaction.

My question is why have Liquid Xenon and Sodium Iodide been singled out as substances that would uniquely respond to the presence of a WIMP by emitting a photon? Why not other liquid elements or crystalline substances?

 

[cesiumfrog]

Maybe this belongs in the subforum "Beyond the standard model" ?

Is WIMP dark matter not part of the current standard model?

 

[humanino]

Is WIMP dark matter not part of the current standard model?

Weakly interacting massive particles in the SM ? At first sight, it does not seem promising. But since we know neutrinos are massive, and weakly interacting of course !, they become good candidates. Unfortunately, massive neutrinos require modifications of the SM to a point that we don't call it standard anymore In any case, neutrinos are so light that they would classify as Light Dark Matter, which is fine as long as you have a whole lot of them. But WIMPs are mostly understood to be supersymmetric partners, which without doubt lies beyond the standard model.

 

[humanino]

I am assuming that WIMPS are the "best" candidate going for the constituants of Dark Matter.

Thanks for stating this assumption explicitely :tongue2:

My question is why have Liquid Xenon and Sodium Iodide been singled out as substances that would uniquely respond to the presence of a WIMP by emitting a photon? Why not other liquid elements or crystalline substances?

You are referring to two specific methods using scintillator materials. There are others, such as EDELWEISS or CDMS, using silicon and germanium cooled semiconductor crystals.

Wikipdedia on WIMPs

 

[malawi_glenn]

Is WIMP dark matter not part of the current standard model?

Nope, rather supersymmetric models as pointed out by humanino

 

[cesiumfrog]

Nope, rather supersymmetric models as pointed out by humanino

I think I've confused context: "WIMP" may be outside of the standard model of particle physics, but for physics in general "some kind of WIMP" does seem to be a part of the mainstream model today. The consensus among astronomers is that "dark matter" exists; bullet cluster lensing stiffened the case for material DM rather than a failure of current gravity theory; MACHO surveys ruled out the next contender; practically anything remaining is caught under the term WIMP.

 

[malawi_glenn]

Yes, but since the only candidate for WIMP's in the (current) standard model is the neutrinos, which can not solve the mystery of the dark matter.

"Unfortunately, massive neutrinos require modifications of the SM to a point that we don't call it standard anymore In any case, neutrinos are so light that they would classify as Light Dark Matter, which is fine as long as you have a whole lot of them. But WIMPs are mostly understood to be supersymmetric partners, which without doubt lies beyond the standard model." - humanino