“Mellon just gave me the money, so I can try things that are high risk,” he says. This allows me to try as many different things as possible.”

WHY ANTIMATTER MATTERS

Scientists have long wondered how insights into the composition of the world could affect reality.

Gerald Gabrielse, Leverett professor of physics, has been searching for an answer for the past two decades.

“Why in the world do we have a matter universe? Why don’t we have an antimatter universe?” Gabrielse, who was on leave this year, says. “At the most fundamental level, we are trying to test how our reality is put together.”

The three basic particles of antimatter—positron, antiproton and antineutron—share the same masses and magnitudes of charge as those of their counterparts in matter—electron, proton and neutron, but with opposite charges. Just as a proton and electron compose a hydrogen atom, an antiproton and positron make an antihydrogen atom. When matter and antimatter particles collide, they destroy each other in a burst of energy.

Professors in the physics community are testing whether antimatter behaves identically to ordinary matter, to understand why matter mostly comprises our universe.

After 18 years of work, Gabrielse, who leads an international team of physicists at the European Organization for Nuclear Research, has already found a way to produce the slowest antiprotons on earth—an important step towards understanding antimatter since the slower the antiproton, the easier it is to measure its properties accurately.

In fact, the antiprotons that Gabrielse studies are 10 orders of magnitude lower in energy than the antiprotons produced in Geneva, the only source of antiprotons in the world.

Chair of the Department of Physics John Huth called Gabrielse’s work a “tour de force.” “It would be a rather tremendous discovery if he found that there were distinct differences between the properties of hydrogen and antihydrogen,” he adds.

This year, in a lab in Geneva, Gabrielse developed novel ways to produce antihydrogen atoms using lasers, map their internal structures and measure their speeds—three techniques which have never been used before.

First, Gabrielse used lasers to excite the electron in a cesium atom into a higher orbit. When the cesium atom collides with a positron, the electron binds with the positron, to create an atom that is half matter and half antimatter. When that atom collides with an antiproton, the positron binds to the antiproton, forming an antihydrogen atom.

“It’s kind of like particle promiscuity,” Gabrielse jokes. “These particles can’t decide what their permanent partners are.”

In addition, Gabrielse’s team was able to measure the distance between the positron and antiproton in an antihydrogen atom by the magnitude of the voltage required to pull the two particles apart, enabling them to better map the internal structure of the atom.

Gabrielse, who also won the Levenson Teaching Award for Science A-45, “Reality Physics,” says he plans to submit his team’s findings this week for publication in Physical Review Letters.