ATLAS at CERN

During my freshman year as a McDermott Scholar, many people asked me where I thought I might want to study abroad, and to be honest, I couldn't decide. At times, I saw myself taking physics classes in Europe or Asia, and at others, I thought I would want to enroll in something vastly different than my major and learn about the ancient Greeks in Greece while reading the Iliad. The only recurring study abroad option that occurred to me, was to work at a large physics lab abroad, and with the Large Hadron Collider's world-destroying black holes in the popular news so often, CERN seemed like a good option.

At the time I didn't know that the 'European' in the European Center for Nuclear Research, or CERN with all of the adjectives switched in french, was taken pretty seriously. As the United States is not a member state, I soon figured out that CERN did not offer the gobs of American student research positions that I had expected, but instead only offered 10 spots for American students. I applied around winter break last year, and was accepted to the program, I believe, because of my previous high-energy physics experience under UT-Dallas professor Dr. Joseph Izen. My experience at Los Alamos National Labs certainly helped as well, and I definitely would not have been able to spend the summer in New Mexico without the McDermott program.

So thanks are sincere and necessary, but, perhaps, do not make for the most interesting read. For that, I'd like to take everyone on a small tour of where I've been working this summer. CERN is located about 20 minutes outside of Geneva on the border between Switzerland and France. It's a great location because you can set your watch on the Swiss trains and buses, and the great food and wine bleeds over from France. Most things above ground at CERN look like modest office buildings, somewhat reminiscent of founder's north on the inside and the art barn on the outside. There are some nicer buildings, but the truly impressive parts of CERN exist underground.

Impressive is a bit of an understatement. CERN houses the Large Hadron Collider or LHC. The LHC lives in a circular tunnel 100m underground, 26km in circumference. It consists of thousands of superconducting magnets that bend a beam of protons in a circle. The beam-pipe is cooled with liquid helium down to a chilly 1.9 kelvin, colder than the residual temperature of outer space. This system of superconducting magnets (essentially electromagnets without electrical resistance) creates a magnetic field of over 8 Tesla, and the entire beam-pipe is also kept in a vacuum with a pressure about 10 time lower than the pressure on the surface of the moon. Oh, and it accelerates protons to 99.99% of the speed of light, focuses them into small, intense packets, and smashes them together at energies up to 7 times higher than previously possible in the lab.

Located along the LHC ring at the points where the machine collides protons, are the world's newest particle detectors. One of these detectors, the one I am working on the summer and the one that the UT-Dallas high-energy physics group works on, is called ATLAS. It's a cool name, but a rather bad acronym standing for A Torodial LHC ApparatuS. ATLAS is a collusus. It is a cylinder of concentic sub-detectors seven stories tall and half a football field long. It weighs over 7000 tons, about as much as the Eiffel Tower in Paris, and the entire thing has to be alligned and calibrated on the micron scale. Each level of the detector is designed to measure different things. The innermost sub-detector, the pixel detector, works simmilarly to a digital camera to measure the precise location of particles that emerge from high-energy proton collisions. The outermost sub-detector is the muon system. It is designed to snag information about a particular particle called the muon (essentially just a more massive electron), and it is this subdetector that can be seen behing me in the accomanying whoosh picture.

My job this summer has been to work on whats called the ATLAS trigger system. The ATLAS detector alone produces enough data fill a stack of CD's that could reach the moon and back, twice, every year, many Terabytes per second. This is, of course, too much data, and many times when protons are smashed together, nothing intersting happens at all. The trigger system is in place to quickly filter through the collisions in real time and save only the interesting ones, lowering the data output rate to about 300 MB/s. This is not as easy as it sounds, considering a focused group of protons called a bunch collide in the detector every 25 nanoseconds; by the time the electronics get the signal that a collision has occured, more collisions have already taken place.

Working at CERN has been very fun, but it was not the only thing that I did this summer. I was also able to travel before the internship started in mid-June as well as on the weekends. I hope to fill everyone in on some of my travels in another blog post coming soon.