Physicist studies particles with Large Hadron Collider database


University physicist Sevil Salur studies particles in conditions similar to the ones only microseconds after the Big Bang.

To research the nature of subatomic particles in extreme heat and pressure, she and her research assistants, including undergraduates Leo Yu and Alex DeMaio, collect data from two large particle colliders and perform elaborate calculations on their movements.

At the Large Hadron Collider in Switzerland and the Relativistic Heavy Ion Collider in Brookhaven, N.Y., researchers collide subatomic particles such as protons, electrons and the nuclei of atoms at high speeds, said Salur, who recently won the undergraduate teaching award for her honors physics course.

Yu, School of Arts and Sciences senior, said his work focuses on refining, studying and plotting information from the massive LHC database.

“We generate graphs based on different cuts of data that we want, since we’re only interested in a small subset of the data,” he said.

The LHC is a particle accelerator that uses magnets to speed up particles as they move through a 17-mile tunnel, Salur said. Researchers there finely tune the force of the magnets so the particles hit each other.

“They’re really delicate machines, a large team of scientists maintain them,” she said. “They’re really more elaborate than a space shuttle.”

The LHC is closed for renovations until 2015, she said. Until then, she had plenty of data to analyze. More than 2,500 people work with data from the LHC, but only 50 to 60 research heavy ions in her team as part of the collaboration.

At the RHIC, the accelerator is not as powerful, but she is able to study varying system sizes.

Salur focuses on the behavior of quarks, which make up all other subatomic particles, and gluons, which hold the quarks together, she said. Under the extremely hot and dense conditions created in particle collisions, quarks no longer behave like they normally do.

“If you put [a quark] into such high-density conditions, it doesn’t really remember what particle it belonged to, so it’ll behave more freely,” said Salur, an assistant professor in the Department of Physics and Astronomy.

Yu said the situation was comparable to an ice cube melting into water. As ice melts, it loses kinetic energy in the high-temperature environment.

“The state of energy in the Big Bang is very high, analogous to the water,” he said. “As the universe expanded, the energy density goes down, which causes a freeze into the particles we have now.”

The first microsecond is a quark and gluon soup, Salur said. After that, the strong force, which binds protons to neutrons and quarks to each other, began to take over and the current arrangements formed.

The only place where these conditions exist now is in the center of neutron stars, Salur said.

Salur said one of the difficulties of finding out what happens in these collisions is they are simply too hot and too high-energy for any current detectors.

Instead of placing the machinery inside the collision, she said, they have to study the particles from a further distance and extrapolate information about the movement and energy of the particles.

“We get the final end product, and then we have to go back and study what really happened,” she said.

Quarks come out of the collision as jets, or streams of particles. Yu said these jets are unstable and decay fast by the time they get to the detector.

“We have to do a reconstruction of the particles,” he said.

So far, there are no practical applications to their research, Yu said, but they cannot be sure what they are going to find in the future.

As undergraduates, DeMaio and Yu did very few of the higher-level calculations, but instead applied filters to the data sets they received from the database, eliminated unnecessary noise from the data and created graphs and plots, DeMaio said.

The environment in a professional laboratory was new to DeMaio, who found the work was more about learning than conforming to a teacher’s standards.

“Your code is pretty much guaranteed not to run correctly the first time, so being stressed isn’t going to help,” said DeMaio, a School of Engineering sophomore.

The team’s work was performed in collaboration with a larger team of physicists from different universities and research groups, Yu said.

“Salur is always on the phone talking with people from around the world,” he said. “It’s really interesting to work in such a large collaborative setting.”


By Erin Petenko

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