Antimatter atoms trapped and stored for the first time

LONDON - An international team of scientists working at CERN, the European Organization for Nuclear Research near Geneva, Switzerland, has for the first time trapped and stored atoms of antimatter.

Scientists from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory and the University of California at Berkeley have made key contributions to the ongoing international effort.

The ALPHA collaboration stored atoms of antihydrogen, consisting of a single negatively charged antiproton orbited by a single positively charged anti-electron (positron). While the number of trapped anti-atoms is far too small to fuel the Starship Enterprise’s matter-antimatter reactor, this advance brings closer the day when scientists will be able to make precision tests of the fundamental symmetries of nature.

Measurements of anti-atoms may reveal how the physics of antimatter differs from that of the ordinary matter that dominates the world we know today.

Large quantities of antihydrogen atoms were first made at CERN eight years ago by two other teams. Although they made antimatter they couldn’t store it, because the anti-atoms touched the ordinary-matter walls of the experiments within millionths of a second after forming and were instantly annihilated-completely destroyed by conversion to energy and other particles.

“Trapping antihydrogen proved to be much more difficult than creating antihydrogen,” says ALPHA team member Joel Fajans, a scientist in Berkeley Lab’s Accelerator and Fusion Research Division (AFRD) and a professor of physics at UC Berkeley.

“ALPHA routinely makes thousands of antihydrogen atoms in a single second, but most are too ‘hot’”-too energetic-”to be held in the trap. We have to be lucky to catch one.”

The ALPHA collaboration succeeded by using a specially designed magnetic bottle called a Minimum Magnetic Field Trap. The main component is an octupole (eight-magnetic-pole) magnet whose fields keep anti-atoms away from the walls of the trap and thus prevent them from annihilating. Fajans and his colleagues in AFRD and at UC proposed, designed, and tested the octupole magnet, which was fabricated at Brookhaven.

ALPHA team member Jonathan Wurtele of AFRD, also a professor of physics at UC Berkeley, led a team of Berkeley Lab staff members and visiting scientists who used computer simulations to verify the advantages of the octupole trap.

In a forthcoming issue of Nature now online, the ALPHA team reports the results of 335 experimental trials, each lasting one second, during which the anti-atoms were created and stored. The trials were repeated at intervals never shorter than 15 minutes. To form antihydrogen during these sessions, antiprotons were mixed with positrons inside the trap.

As soon as the trap’s magnet was “quenched,” any trapped anti-atoms were released, and their subsequent annihilation was recorded by silicon detectors.
n this way the researchers recorded 38 antihydrogen atoms, which had been held in the trap for almost two-tenths of a second. (ANI)