Johns Hopkins Gazette: August 5, 1996

On Astronomy:
David Gerdes Retools
For His Study Of The
Top Quark

Award: Research effect
earns him Outstanding
Junior Investigator prize

Emil Venere
News and Information

David Gerdes played an important role in tracking down the top quark, but perhaps the most exciting work lies ahead.

An international team of scientists is revamping the machinery used to produce and detect subatomic particles so that physicists can begin learning more about the enigmatic top quark.

Gerdes, an assistant professor in the Department of Physics and Astronomy, has received a financial boost to further his work in that direction. His proposal to upgrade a system needed to study the top quark earned him an Outstanding Junior Investigator award, which provides $85,000 a year for three years. Only recently appointed, non-tenured faculty are considered for the awards, issued by the U.S. Department of Energy.

A team of 450 scientists verified the existence of the top quark in 1994. It is believed to be one of the final fundamental building blocks of matter to be confirmed by research.

"The top quark discovery was our collaboration's finest hour," said Gerdes, a member of the team that made the discovery.

Unlocking the mysteries of the top quark, however, may be even more exciting than finding it. Why, for example, is it so heavy--200 times the mass of a proton and also far heavier than its quark counterparts?

Learning such secrets could lead to profound revelations about why the various subatomic particles have the masses that they do, a major puzzle of quantum theory.

Over the next three years, the international collaboration will upgrade the equipment so that scientists can make more top quarks, which is essential to study them properly.

Up to this point, physicists have produced only a few dozen top quarks.

"That's not very many," Gerdes said. "The next thing you want to do is make lots of them and study them in a very detailed way."

"But rebuilding large expanses of the detector in just three or four years is a very tall order, even for 450 people," Gerdes said.

Proving the top quark's existence provided crucial support for the Standard Model of physics, a widely accepted theory about the nature of matter and energy. The theory says that all matter consists of elementary particles called leptons and quarks, with the six varieties of quarks grouped into three sets of "twins": the up and down, the strange and charm, the top and bottom. The quarks are bound together by particles called gluons to make the common particles like protons and neutrons.

The Standard Model also predicts the existence of something called the Higgs particle.

"It's the thing that is supposed to actually give everything mass," Gerdes said. "The top is the particle that interacts most strongly with the Higgs, so it could be that this is the particle that could lead to something really basic about the Higgs."

Scientists produce top quarks by smashing together certain types of subatomic particles at the Fermi National Accelerator Laboratory in Batavia, Ill. Protons and their antimatter equivalents, antiprotons, are whipped around a circular track by a series of powerful superconducting magnets. When they collide they create an ultra-high-velocity spray of matter's most elementary particles, which are then tracked by sophisticated detectors.

Gerdes' job is to upgrade one of those detectors so that it will be able to keep up with the increased production of top quarks once the souped-up system is operational.

He is heading a Hopkins team that is improving a device called the outer tracker, a key component in a huge tracking system used to identify top quarks; the device measures the momentum of subatomic particles created in the collisions.

To give an idea of the device's complexity, it will contain about 5,000 printed circuit boards, which will be designed, built and tested at Hopkins. Gerdes is working with associate research scientist Zhong Feng, engineer Joseph Orndorff and graduate student Joao Guimaraes da Costa.

"The tracking system is really the central instrument of the detector that's used to study the top quark," Gerdes said.

Put more simply, without the upgraded tracking system, the improved accelerator would be useless.

Gerdes isn't the only Hopkins scientist upgrading vital Fermilab hardware to investigate top quarks. Physics professor Bruce Barnett and several students will help improve a vital component known as the silicon vertex detector.

Both Barnett and Gerdes work on the same team of scientists, in an experiment known as the Collider Detector at Fermilab, or CDF. They have been competing against another team of physicists at Fermilab, who are collaborating on an experiment known as DZero.

Physicists had hoped one day to use an advanced accelerator called the Superconducting Supercollider, which was to have been built in Texas, to learn about the top and Higgs particles. But that project was canceled several years ago, and scientists now plan to use a future European accelerator, called the Large Hadron Collider, which should be completed in about a decade.

However, until then, Fermilab has the only accelerator powerful enough to make top quarks.

"We have a tremendous opportunity," Gerdes said. "It's a new fundamental particle that we are just beginning to study."

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