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My Research: Cosmic Rays
One of the first questions I always get asked when I tell people I am a physicist is what I research. So I wanted to share a brief explanation of that and some of the things I've done here. This is really a brief explanation. A more complete explanation of my graduate work can be found in my thesis. A warning before you click on that link - it is over 200 pages and 7.73MB (so not a small file). But does cover much of what I do.
To understand what I do, you will first need a basic understanding of particle physics. Basically, particle physics is the science devoted to understanding what matter is made of and how it interacts with other matter. As the pieces of matter we examine get smaller, it gets harder and harder to look at them. When they get really small, really the only way we have of looking at them is to slam particles into each other at high velocities and watch what comes out. This is basically how particle accelerators work.
The only problem with that method is getting high velocities. The faster you want something to go, the more energy you have to give it. It gets harder and harder - and hence more and more expensive - to give particles that energy. The solution to this problem is provided to us by nature. There are plenty of objects out there that can provide high energy particles. Take the sun for instance. It is very good at throwing lots of high energy particles at the Earth. These particles hit the atmosphere and interact with it. There are actually a large number of sources for these type of particles. We call these particles from outside of our atmosphere cosmic rays.
There is only one problem with natural sources. To get high energy particles, you must have high energy sources. The sun is actually a fairly low energy source for cosmic rays. Things like pulsars and black holes could produce very high energy cosmic rays but are fairly rare. So you need bigger and bigger detectors to measure enough of them to get decent statistics.
My research is based on the very highest energy cosmic rays. That means they are very rare. It also means they are very exciting.
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Why is it exciting? Well, the particles I looked at have energies that have a billion times more energy than the highest energies we can achieve in ground based accelerators. They are on the very edges of what we understand. That means they are a great place to look for new physics. Major research in these areas focus on the spectrum, the sources, and the composition of these cosmic rays.
My research was in the area of composition. Specifically, I was looking for types of particles that have been predicted but never seen. I did this by examining the speed of the incoming particles. If you don't want to read my entire thesis, my results are summarized in a power point presentation and a poster that I presented at the 2009 ICRC. |
Specific Research Skills
I don't want this to sound like a CV, but I figure after as much work as I spent on my thesis it wouldn't be too out of line to show my work off some. So here are some pictures and explanations of what I have done. Most of my analysis work was done on a computer. It involves computer programming. This involved writing a lot of code for physical simulation, Monte carlo, and data analysis. Here are some brief samples. |
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This is a picture of the geometry of an incoming particle. When the particle strikes the atmosphere, it interacts and causes what looks like an upside down tree. That is called the air shower. The largest challenge in looking at very high energy particles is that they are very rare. It is difficult to measure them directly. In order to build a detector large enough to measure a good number of them, we measure them indirectly.
This means part of the problem is figuring out what properties the original particle had in the first place from the signals we observe. For my research, this involved calculating the geometry of the shower we observed and using that geometry to calculate the speed.
Doing this by hand would be impossible given the amount of data we recorded. So instead, this work required me to write computer software to do it for me (unfortunately, there is no off the shelf software for this type of analysis). All in all, this totaled some tens of thousands of lines of code performing physical analysis, error checking, statistical calculations, and data management.
The following are some of examples of what the code did. This is by no means inclusive, or even the best of the work. But they are some fun examples. |
Some plots of the data sorting to remove noise and fitting process to obtaina speed. These don't shrink as well, so I've just included links to them.
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One of the various statistical plots produced during the analysis. This particular plot shows the correlation between speeds for the two detector sites. This correlation was expected as the geometry calculation is a combination of the observed events for both sites. This plot was a sanity check to make sure the results were given as expected. |
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This is a sample of the results from real data with no quality cuts applied. It shows distinct peaks at the speed of light for downward going events, the speed of light for upward going events, and a large amount of noise. The graph is compressed and probably doesn't translate well. You can click on it for a full view. |
These plots show the resulting histograms for the search.
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| Finally, as part of my search I found several possible candidate events. Part of this involved trying out other possible physical explanations. Because the speed was based on the reconstructed geometry of the event, trying different geometries was one of the methods used. This was done by writing code that could perform an arbitrary rotation of a plane in 3D space and then comparing the results to the viewed photo tubes. Here is a sample of an arbitrary rotation onto the z axis. |
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| These are just a few of the pictures that translated to the web better than others. My thesis includes more, as does the presentation. While I would like to detail all of my work, that took over 200 pages in my thesis. Still, I hope this is a small sample of what I do. |
