Week of January 15

Happy New Year! At the end of last semester, I was at a pretty good place with my internship. I'd spent a good amount of time learning technical skills, and by the last few meetings, I had started writing code for data analysis. This semester,  my first goal is to finish the preliminary calculations for the hybrid meson. Here's a quick recap to remind you:

From 1999 to 2008, the SLAC National Accelerator Laboratory at Stanford conducted the BaBar experiment, which involved hundreds of researchers using the BaBar detector, a multilayer particle detector, to study the difference or disparity between the matter and antimatter content in the universe. The experiment is no longer running, but there are years of data that have yet to be analyzed. My job is to run a code on Python that analyzes a very specific section of the data to determine whether or not it is worth further analysis. In particular, I am searching for evidence of a new type of particle called an exotic meson, which has already been predicted to exist.

The calculations are actually much simpler than the data analysis on Python I've been doing. All I have to do is figure out how many of these mesons we can expect to see in the data (if they do in fact exist). But, before I do my calculations, Dr. Bellis wants me to understand a little bit more about the BaBar experiment itself. 

So, to give me an idea of the sort of work that scientists at BaBar did, he gave me a paper that he co-authored at Stanford to read. It's called (get ready for it, it's a mouthful) "Observation of new resonances decaying to D/pi and D*/pi in inclusive e+e- collisions near s=10.58 GeV." The paper basically describes a certain type of decay that the BaBar detector measured. It was really cool to read the paper and see that they included mass distribution graphs for the particles, which are the same graphs that I've been making in Python!

The detector measures the momentum of charged particles using a huge magnet, which contains an SVT or silicon vertex tracker and a DCH or drift chamber. The SVT consists of five layers of double-sided silicon detectors, which transmit the position measurements of the particles to an integrated circuit. The DCH is a gas-filled chamber that provides the momentum measurements for charged particles. Here's some more information about the components of the detector: http://www.slac.stanford.edu/BFROOT/www/doc/workbook/detector/detector.html

The link also explains why the magnet is important: "Without a magnetic field, a tracking device could not measure charge or momentum, but only position. But when a magnetic field is present, the charged tracks curve, and the charge and momentum of the particle can be determined from the direction and curvature of the track."

Although I won't be directly using this information, it was still fascinating to learn, and it gave me a good sense of how intricate this experiment really was.

The paper also provided a great table listing the resonance, efficiency, mass, and width (among other things) of certain D mesons. I'll be using some of these numbers in my calculations, so it was really helpful to see where these numbers actually came from and how they were calculated.

I spent most of my time trying to make sense of the paper. It was pretty hard to get through, especially since I didn't understand every other word used. At first, I was intimidated by all the technical language and crazy looking graphs, but then I realized that a lot of the calculations that the physicists did just came from the mass-energy-momentum equivalence. Most of particle physics is intimidating at first, but, like the universe, it is remarkably simple at its core.