Researchers Prove Equal Proton, Antiproton Mass

In a step toward confirming the widely accepted theory that for every matter particle there exists an antimatter particle of equal mass, two Harvard physicists proved that protons and antiprotons have the same mass to at least the tenth decimal place.

Although similar experiments have been performed in the past, Professor of Physics Gerald Gabrielse and graduate student Anton N. Khabbaz were able to achieve an "unprecedented level of accuracy" in their tests.

"This experiment has been done before but to less accuracy than we achieved this time," Khabbaz said. "We improved the measurement by about a factor of one million."

The antimatter counterpart of protons, antiprotons are believed to be exactly the same as protons except that they have a negative charge instead of a positive charge. Antimatter is not generally found in nature.

Because matter and antimatter annihilate each other upon contact, Gabrielse and Khabbaz isolated the antiproton in an electric and magnetic field to prevent it from touching any matter during the experiment.

Gabrielse and Khabbaz then added a negative hydrogen ion--a proton with two electrons around it--to the field. While the two particles moved in circular orbits, Gabrielse and Khabbaz measured the frequency at which each of the particles oscillated with a very sensitive radio.

"We measured the radio station that is one antiproton...and we listened to one proton...and we compared back and forth to see if they have the same oscillation ion frequency in the same field [to determine] if they have the same properties," Gabrielse said.

The experiment indicated that antiprotons and protons do oscillate at the same frequency and thus suggests that they have the same properties.

"What we were able to do at an unprecedented level of accuracy [was] to tell that the proton and antiproton have the same frequency," Gabrielse said.

Gabrielse and Khabbaz used a negative hydrogen ion instead of a proton in the experiment because it allowed for greater accuracy of measurement after correcting for the additional electrons of the ion.

Although the experiment was led by

Harvard physicists, it took place at the CERNEuropean Laboratory for Particle Physics inGeneva, an international laboratory which includesamong its members a host of European countries.(The U.S. is an observer state.)

Gabrielse and Khabbaz worked in collaborationwith the University of Bonn.

The physicists announced their results a fewweeks ago at a CERN conference. Gabrielse andKhabbaz have been working on this experiment forthe last two and a half years, and Gabrielse hasbeen working on similar experiments for a decade

Harvard physicists, it took place at the CERNEuropean Laboratory for Particle Physics inGeneva, an international laboratory which includesamong its members a host of European countries.(The U.S. is an observer state.)

Gabrielse and Khabbaz worked in collaborationwith the University of Bonn.

The physicists announced their results a fewweeks ago at a CERN conference. Gabrielse andKhabbaz have been working on this experiment forthe last two and a half years, and Gabrielse hasbeen working on similar experiments for a decade