Sifting Through Millions of Megabits

Patrick Chinn
pchinn@uoregon.edu

CERN's Large Hadron Collider, which came online September 10th, is a massive project, both technically and collaboratively. For example, the raw data "coming from the experiment will be about 1 petabyte per second," said David Strom, University of Oregon Professor of Physics. That's one million gigabytes of data per second from one of four main detectors in the LHC.

Strom's job on the project is to work with 80 other physicists around the world to write triggers, the software that will pare the data down to a manageable size. "This is an important job because the events we throw away are gone forever," Strom said. "Each second we can only keep 200 of the 40 million events produced. The vast majority of events must be rejected."

Working with Strom is Eric Torrence, Associate Professor of Physics at the university. Torrence said that the data is first processed by high-speed pattern matching hardware, which has about two microseconds to make a decision on whether to keep or discard the data. From there, the data is fed into a processor farm, "1,800 nodes of dual-processor Xeon boxes," said Torrence. "The fastest production boxes we can get a hold of." The data is stored locally and then distributed over multiple 10 Gbps network links via research networks like GEANT2, ESnet, USLHCNet and Internet2.

The collider itself works by speeding protons at just below the speed of light in opposite directions around a 17-mile circuit and then smashing them together. Not only is the amount of data generated tremendous, but so is the power. "The energy stored in the beam is comparable to the energy of a 747 jumbo jet coming down the runway at take-off," said Jim Brau, University of Oregon Knight Professor of Natural Science.

One of Strom's colleagues at the university, Graham Kribs, said that the point of these experiments is to answer questions about what we are made of, what the universe is made of, and how nature works at its most basic, fundamental level. And as a theoretical Physicist, Kribs said it is also a "search for something we've never thought of, things that we don't expect."

Brau, Kribs, Strom, and Torrence are four of 2,500 physicists working on the ATLAS experiment. The project has representatives from 37 countries, 169 universities, and includes 700 students. Four UO graduate students are working on the project.