Sunday, October 17, 2010

Update on my job

I'm still trying to decide what my next topic should be, but I figured I'd tell everyone a little about what I've been doing in my new job. As we might recall, I started a postdoc in July at Fermilab outside of Chicago. In my new experiment, COUPP, I'm still looking for dark matter, but the way we go about it is very different. It's probably worth reiterating how the whole dark matter search works, or you can also read over some of the summary posts on the side bar. To recap a portion of those entries, we are pretty sure that dark matter of some kind exists, and we know this gravitationally; I've described in detail rotation curves and the CMB in prior posts, and there are other observations that support the conclusion that there is some form of matter out there that we can't see.

There are certain classes of theories that predict dark matter might be a new type of particle, one that only interacts weakly. These particles would theoretically be all around us, just like neutrinos produced in the atmosphere and the sun (the villains in the ridiculous, apocalyptic movie 2012 from two years ago from whence comes the picture to the right, that I was quite happy to find my father had rented when I went home for a weekend. A friend of mine at Fermilab, Dave Schmitz, blogged about the physics behind the premise to 2012 back when it came out) that constantly stream through. Every once in a while, we expect these hypothetical particles to hit something on earth, and so we build detectors to catch those hits. At this point, we know that dark matter can't interact more than a handful of times per year in the most sensitive detectors we know how to build. Unfortunately, these detectors are also sensitive to any other radiation that's flying around - say at a rate of about 100 times per second. Or 4 billion times per year. And we are looking for a handful of events.

This is the problem with backgrounds that I went into in detail in those early posts. I said there that the majority of those backgrounds are "electronic recoils," where the radiation has hit an electron in the detector. My new experiment is something called a bubble chamber, which was used a great deal in the heady days of high energy particle physics in the 60s and 70s. They aren't used for high energy work anymore, but we've repurposed the technology for our experiment. In our bubble chambers (and I think I will have to talk about the physics a little at some point), we can set it up so that electronic recoils don't do anything in the detector - we are effectively blind to the main background to dark matter searches!

That's probably a bit more setup than I wanted. Because what I really wanted to say (in one paragraph only) was that I spent all day Friday in a jumpsuit (I do love the jumpsuits) with a full face mask respirator (requiring me to shave the beard I had grown while writing my thesis) trying to shove a 1/2" steel pipe down the neck of an incredibly expensive, delicate, and very clean (for radioactivity purposes) glass bell jar surrounded by a stainless steel vessel (making it rather difficult). And failing. Physics isn't all math and equations and brilliance. In fact, for me, most of the time, it's working down in a tunnel doing plumbing, rebooting computers ("wait, it's not working? Have you tried rebooting it yet?"), or trying to carefully put a steel tube in a pressurized glass jar filled with red fluid that might or might not contain HF acid and a poison gas used in WW1. So all in all, pretty fun, even when it doesn't work.

My experiment


  1. Cool picture, although I cannot discern what is what. I like COUPP! (Says a former PICASSO person, I'm practically a collaborator...) And I really do miss the practical aspects of experimental physics.

  2. did he just search a pin on that bunch of grass?