December 18, 2009

Dark Matter Matters

As a card carrying astro-related blog owner I am contractually obligated to comment on yesterday's kinda-sorta-it-might-be-dark-matter-semi-quasi-announcement by the CDMS II group.

There had been rumors about this thing for over a week that CDMS had some kind of watershed announcement. That they had discovered dark matter (what other important announcements can DM detection projects make?), that they were publishing in Nature today, that a torrent of papers was about to hit the arxiv with analysis of this last night, that they had all learned the true meaning of Christmas and were going to be nothing but kind and generous from now on.

Yesterday, with the hype reaching a fever pitch, they held a seminar on their findings, broadcast online. Unified in the concerted effort to drive everyone crazy in anticipation they began the lecture with about 10 minutes of freshman-astronomy-level rationales for the existence of cold dark matter, before moving on to another 10 minutes of descriptions of things that were important to them but not to us, like the arrangement of the detectors and the way the data was collected. Then she threw in a joke about a spherical cow, and stalled for another 5 minutes. Finally, she got to a slide that said "Results" or something at the top, and the video completely froze. Of all the panicked, oh-my-god-just-tell-us-already, freakouts I can imagine something causing, this was way up there. When I regained consciousness and the video started working again she was on a slide that said "Conclusions," and before I could make out any of the bullet points, the camera quickly panned away and she started taking questions. It was awesome.

Anyhow, in the aftermath of that humbling experience, what actually transpired during those missing minutes has come to light. CDMS detected TWO events. But because of the way they pull events out the noise of other stuff hitting the detector that could appear as a false signal, they'd expect to find about 0.8 events in the time the experiment ran. There is a 23% chance that what they saw was just random noise. I read someone describe this as the least helpful possible result and I have to agree. It isn't enough to be a conclusive discovery, and it isn't enough to say that dark matter definitely ISN'T being seen in this kind of detector either. So unfortunately, not enough for solid results, and not much to come up with a decent parameter space constraint either. It could certainly turn out they did find it, but that will have to wait for later confirmation. Just a lot of build up, a suggestion that we might be on the verge of learning something really interesting, a clue, and then the realization that nothing has been settled and you'll have to keep waiting for answers. Kind of like an episode of Lost.

Best popular article about this I've seen: Scientific American
Cosmic Variance Liveblog of Yesterday's SLAC seminar.
Basically alright article with a non-sequitur about supersymmetry: NYTimes

Actual CDMS Paper