This experiment is set to launch on the shuttle in February. It was designed to look for antimatter in cosmic rays. Supposedly this will answer the question of whether or not “dark matter” is real. But not everyone is convinced. Opponents say that even if the results are positive, it won’t settle the matter.
So will it?
What exactly (as non-technically as possible - if possible) is the connection between dark matter and anti-matter?
My (shaky) understanding is that there is no connection between the dark matter and the anti-matter that this spectrometer is looking for. It is a general enough detector of cosmic radiation that it has multiple applications. One application is looking for cosmic radiation from the annihilation of dark matter particles (these dark matter particles and their annihilation when they “run into each other” is a prediction of supersymmetry). Another application is looking for anti-helium zipping around as a remnant from the big-bang.
Some theorized sources for darkmatter would occasionally react with each other and produce anti-matter. An experiment earlier in the year saw an excess of positrons that was thought to be a such a signature, though there seems to be a lot of debate regarding that interpretation.
Btw, since we are on a related topic, is my interpretation of your handle correct?
Exactly. I’ve been meaning to put that in the current thread about user names but haven’t gotten to it.
I’ve always been a frustrated scientist but never felt I had the ability to pursue it. So I’ve settled for being an avid gawker.
When I registered here it was soon after reading an article about something at Fermilab. I liked the sound of the name and figured it was suitably obscure. Of course once they shut the whole place down, it will be really obscure - gotta love that. Also, with LHC, they don’t seem to be gettin’ the love they once did and I wanted to do my part. 
That’s kind of funny. In Norwegian, DØ would mean “DIE!” No idea why they used the letter ø there.
It’s not a letter to Americans. It’s the number zero.
The slash is to distinguish the character from the letter “O”, otherwise the name of the experient would appear to be “do”. “D0” itself refers to the experiment’s location around the collider ring. (Other locations would be A0, B0, …, or D1, D2, … . The CDF experiment is at the B0 location.)
It depends what they see. Also, AMS has multiple goals, not all related to dark matter. Even if the dark matter measurements turn up nothing, AMS can set tighter limits on the presence of antimatter in the universe – as far as we know, there are no antimatter galaxies out there – and it can greatly improve over existing cosmic ray flux data. But, since the OP is about dark matter:
If dark matter is made of the right sort of yet-undiscovered particles, these particles could be annihilating with one another throughout the galaxy, and those annihilations could produce anti-electrons (a.k.a., positrons), which AMS could detect. (A recent experiment called PAMELA saw an unexplained excess of positrons, but they did not see a corresponding excess of antiprotons, which many dark matter models expect).
Two big difficulties with AMS’s dark matter search:
(1) The universe is complicated. There are many poorly understood sources of high-energy particles out there. If AMS sees an excess of positrons or antiprotons, all that indicates is that there is an unknown sounds of those particles. That source may or may not be dark matter. If the observed rates and energy spectra are consistent with certain classes of dark matter models, that would strengthen things some.
(2) We don’t know what dark matter is, or how often it should be annihilating (both due to its nature and due to the “clumpiness” of its distribution throughout the galaxy). So, if AMS doesn’t see an excess, it doesn’t mean there isn’t dark matter of the appropriate type.
In the end, any dark matter data from AMS alone will necessarily range from “not exciting” to “very exciting, but inconclusive”. But that’s no reason not to make the measurement! If every individual experiment had to be conclusive to be worthwhile, we wouldn’t have made it very far in physics. It’s often the build-up of many “exciting, but inconclusive” results that lead to, in time, a defensible conclusion. This is especially so with dark matter, as “exciting, but inconclusive” results is the name of the game. The most solid understanding will come if dark matter allows for all three of the following to happen: (a) the LHC produces and detects DM-candidate particles, (b) indirect measurements like AMS see DM annihilation products, and (c) direct measurements like CDMS and XENON (and many other) see the direct interaction of DM with ordinary matter. You could sensibly argue that you need at least two of these to say that you’ve “found” dark matter. (The ways out to squirm out of a dark matter explanation are different in each case, of course.)
A lot of the apparent vitriol in the linked NY Times article relates to the project’s approval process, though. Shuttle missions and ISS berths are precious resources, so you want the process of doling them out to be as fair and transparent as possible. Some in the cosmic ray and space-bourne experimental sciences think that wasn’t the case here, but others aren’t so bothered.
Note that there are at least a couple hypothesized types of dark matter, some whose annihilation could produce anti-electrons (hidden-sector WIMPs), and then the more traditional WIMPS (weakly interacting massive particles) like neutralinos whose annihilation would not produce anti-electrons (more likely photons, for example). My understanding is that AMS is a general enough detector to observe either possibility.
Your understanding is correct. AMS is a surprisingly generalized detector for being space-bourne. It’s ability to distinguish positrons and protons cleanly is another important feature. But, these are minor details given the scope of the OP, I’m assuming.
Thank you to iamnotbatman and simplicio, and especially Pasta for your detailed responses.
OT: I was thinking about starting another thread regarding the standard models prediction regard the energy density of the zero point field. This seems to be a major embarrassment for the model and would like to hear it discussed. Do you all think it would be a good topic and if so, should I put it in GD or GQ. Thanks again.
Eh, what’s a few hundred orders of magnitude, between friends?
Keep in mind that the Standard Model is not capable of actually making a prediction of the zero point field, just an estimate. It wouldn’t surprise anyone all that much if there were a bunch of miraculous cancellations, and the correct answer turned out to be exactly zero. The embarrassing part is that it appears to not be exactly zero, but to nonetheless be insanely incomprehensibly smaller than the estimates. Personally, though, my money is on the genuine zero-point field being genuinely truly zero, and the “dark energy” being completely unrelated to it, and just happening to look qualitatively just like a zero-point energy.
Could generate some interesting debate… but IMO I doubt you’ll be able to trust anyone’s opinion on the subject. Depends exactly what you are asking (so be precise). Technically the vacuum energy is not an embarrassment per se (renormalization is well accepted), and everyone agrees that we don’t yet have a theory of quantum gravity, so nothing here is really that surprising. But the very tiny cosmological constant is a bit of a mystery given that any attempt to calculate it predicts an obscenely enormous value. Fine tuning, however is not an isolated problem in physics.