AEgIS installation completed

Gravity. Despite first being described over three centuries ago, it remains one of the least understood of the fundamental forces explored by physicists. At CERN’s recently completed AEgIS experiment, a team has set out to examine the effect of gravity on an as-yet-uncharted realm: antimatter.


The complete AEgIS set-up.

Located in the AD hall, the AEgIS experiment plans to  make the first direct measurement of Earth’s gravitation effect on antimatter. By sending a beam of antihydrogen atoms through very thin gratings, the experiment will be able to measure how far the antihydrogen atoms fall and in how much time – giving the AEgIS team a measurement of the gravitational coupling.

“By the end of 2012, we had finished by putting all the elements of the experiment together,” explains Michael Doser, AEgIS Spokesperson. “Now we have to show that they can all work together and, unfortunately, we will have no antiproton beams for a long period due to the machines’ shutdown.”

But instead of waiting for two years for beams to return to the AD hall, the AEgIS team has come up with an alternative. If they can’t work with antihydrogen, why not try out their experiment with hydrogen? By replacing antiprotons with their own proton source, the AEgIS team will be able to manufacture their own hydrogen beam that they can use to commission and test their set-up. “We want to make sure we understand how to make antihydrogen and our diagnostic will be the formation of hydrogen,” says Doser. “If we succeed in making hydrogen this year, that will be a huge step forward; and if we can make hydrogen beams next year, then we’ll really be in business.” Surprisingly, carrying out the experiment with hydrogen will technically be more difficult than it would have been with antihydrogen. The AEgIS team is pushing the technology hard to develop a suitable detector.

One main challenge will be in the production of positronium* used to create hydrogen. The AEgIS team will be faced with a Goldilocks-style problem: making sure it is not too fast, and not too slow. “The positronium needs to be fast enough to ensure it doesn’t quickly decay before it meets the protons/antiprotons,” explains Doser. “But it can’t be so fast as to pass the protons/antiprotons altogether. Tuning this will take quite some time and will be one of the first things the team works on.”

The AEgIS team will be carrying out this commissioning during the coming months, opening up their set-up next month to make any necessary adjustments and to install a hydrogen detector and proton source.

* Positronium: an electron and a positron in a bound state.

by Katarina Anthony