April 18, 2003

Inside the Particle Accelerator

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The fourth in a series of articles on hidden treasures at Cornell.

Something is buried under Cornell’s playing fields. Fifty feet below the surface of the earth, next to Wilson Lab, there is a ring-shaped tunnel roughly half a mile in circumference. Here, scientists work day and night to unlock the secrets of the universe.

Sound like an urban legend or the plot of a science-fiction movie? It’s not: it’s the Laboratory for Elementary Particle Physics’ (LEPP) particle accelerator.

The LEPP, which was once known as the Laboratory of Nuclear Studies, first opened immediately after World War II. It has gone through several different phases over the years, and the current facility was constructed in 1979. The particle accelerator runs 24 hours a day, seven days a week with the exception of maintenance and improvement periods. The cost of energy, maintenance, equipment and staff salaries is covered by an annual budget of approximately $20 million.

At this point, students who don’t know much about physics are probably asking what all this means.

Prof. David G. Cassel, physics, associate director of LEPP, was more than happy to answer that question.

“It accelerates particles,” he said with a smile.

The particle accelerator consists of four parts: the linear accelerator (linac), the synchrotron, the Cornell Electron-Positron Storage Ring (CESR) and CLEO.

It all begins in the linac. Here, electrons are accelerated to an energy of 300 million electron volts (eV). A regular flashlight battery has 1.5 eV of energy, so this is equivalent to sending an electron through 200 million flashlight batteries stacked end-to-end. Although theoretically possible, “doing this with a stack of flashlight batteries is not a good way to do it,” Cassel pointed out.

In the next step, the electrons are injected into the synchrotron where they are further accelerated to an energy of five billion eV.

“The idea is to accelerate particles to energies that are so high that they are traveling at almost the speed of light,” Cassel explained.

At this point, the electrons are injected into CESR. The steps leading up to this only take a few minutes, but the electrons remain in CESR for roughly an hour.

At the same time that this is happening to electrons, the positrons — which are the antiparticles of electrons — are going through the same process but traveling in the other direction. The electrons and positrons, which remain at five billion eV, then crash into each other in a section of the accelerator known as the CLEO Detector. All of this is done in an effort to understand elementary particles.

“As far as we know, the world is made of 12 elementary particles,” Cassel said.

These are further split into two different categories, he said — leptons and quarks. The leptons include electrons, muons, taus and neutrinos. The quarks have slightly less scientific-sounding names. They are up, down, charm, strange, top and bottom. Contrary to what many students may believe, protons and neutrons are not elementary particles; they are actually composed of a combination of “up” and “down” quarks.

When the electrons and positrons in CESR collide, they form B mesons and anti-B mesons — “bottom” quarks and their antiparticles. This demonstrates a fundamental principle of physics.

“There’s no way to create particles without creating antiparticles in the process,” Cassel said.

At this point, Cassel’s explanation takes a more theoretical turn. Assuming that the big bang theory is correct, equal amounts of matter and antimatter should have formed when the universe was created. However, most if not all of this antimatter seems to have disappeared, he said. Theoretically, there are three things needed to explain the disappearance of antimatter, and one of them is something called a CP violation.

A very small amount of CP violation was observed in “strange” quarks in 1964. That is one of the main reasons for the research with quarks.

“We’re trying to relate that [observation from 1964] to the CP violation that got rid of the antimatter for us,” Cassel explained.

Although the leading laboratories for studying this phenomenon are currently at Stanford and a Japanese facility called KEK, Cornell has a distinguished history in the field.

“For a good 20 years, we were the best facility in the world for studying B mesons,” Cassel said. “And most of what’s known about B mesons and what’s known about properties related to CP violations and mesons comes from the CLEO experiment.”

Cassel was, however, anxious to point out that the CLEO experiment is not purely a Cornell effort. It’s actually a collaboration of roughly 130 physicists and 19 different universities.

Some of the people involved with this research are students. This year, there are 40 graduate students — 15 from Cornell — and roughly 50 undergraduates working in the field. According to Cassel, this is a great opportunity for students because “they can do something that will actually contribute to the research effort of the lab.”

One student who has done that is Derek Kingrey ’03. Kingrey, who has been involved with the program since he was a freshman, works with the superconducting radio frequency group. His research focuses on “the ‘acceleration’ part of the particle accelerator,” he said.

“The experience has definitely been beneficial,” Kingrey said, citing the experience he has gained in lab techniques and various branches of physics, chemistry and engineering.

Kingrey admitted that he has not been directly involved with the general research being done, but added, “My feeling though, in working in the lab, is that professors and other researchers are excited about new ideas for future uses of the accelerator.”

Cassel agreed that the researchers are passionate about their work.

“I think the way that the larger numbers of students really benefit [from the particle accelerator] is that by having a facility here like this, we tend to attract really first-rate people to the faculty of the University.”

Cassel went on to say that the faculty are just as enthusiastic about teaching as they are about their research.

“We try very hard to communicate this excitement and this interest to these students that we’re teaching,” he added.

Currently, LEPP is in the process of shutting down the accelerator to make changes to some of the equipment. These changes are necessary, Cassel said, because the program is starting to change its focus.

“We’ve contributed what we can to the direct understanding of the B quark,” he explained, “so we’re now going to turn ourselves into the world’s best facility for studying the charm quark.”


Archived article by Courtney Potts