Hi From Denver

I’m in Denver for the 2009 American Physical Society (APS) April Meeting. You might be saying, Wait! It’s not April anymore! And you would be correct. This meeting, which consists of particle physicists, astrophysicists and nuclear physicists, is traditionally in April. There is another yearly APS meeting, the March Meeting, which is for everything else. To distinguish the two they call them by the months in which they’ve traditionally been held.

This meeting consists of 4 days of 10 minute talks mostly by graduate students and post-doc, interspersed with longer plenary style talks from important invited speakers. I’m giving a talk tomorrow morning in the Instrumentation in High Energy Physics session. I’ll be talking about ATLAS’s tracking performance with cosmic rays. Even though the LHC is not running, the ATLAS detector is, and luckily Mother Nature provides us something to look at. (Actually, it's not running this Spring in order to do some maintenance.) The earth’s atmosphere is constantly being bombarded by particles from space which we call cosmic rays. Hundreds are passing through you right now. Modern particle physics was founded on the study of these particles, which can reach much higher energies than we can create in accelerators. ATLAS is 100 meters under the ground, so we see only one type of cosmic ray, the muon, which is created when a primary cosmic rays hits the Earth's atmosphere and decays. Particle physicists love muons. They are heavy and only interact via the electromagnetic and weak forces so they pass through most material relatively unhindered. Last fall ATLAS used these particles to start understanding how the detector works. It is such a massive machine that it takes an immense amount of calibration work before you can start doing physics. The cosmic rays give us a perfect opportunity to do that calibration in a simple environment since we usually see only one of them at a time. In a proton collision like what the LHC will deliver we will see hundreds! I’ve been looking at the performance of our Inner Detector, a set of 3 tracking detectors which work together to measure a particle’s trajectory and momentum. The conclusion of the study is that it is performing very well!

The picture is an artist's rendition of the showers of particles produced when ultra high energy cosmic rays interact in the atmosphere.

There is word that some exciting results will be released tomorrow. I’ll probably write about that and I’ll be writing posts through out the rest of conference as interesting topics come up!