Deflecting antiprotons: the AEgIS technique

A paper from the AEgIS collaboration in today's Nature Communications explains an ingenious method for measuring the deflection of antiprotons.

Antiprotons are the antimatter counterpart to protons – they are the same weight as protons, but with a negative charge. When protons and antiprotons come into contact, they annihilate, producing new particles.

The primary scientific goal of the AEgIS is the direct measurement of the Earth's gravitational acceleration, g, on antihydrogen atoms, which are made up of an antiproton and the antiparticle of the electron, a positron. It will do this by measuring the gravitational deflection of a beam of antihydrogen. Today’s result is an important step on the way: a test using antiprotons in place of antihydrogen demonstrating that the basic idea for detection is sound.

The AEgIS technique involves passing antihydrogen through a device called a moiré deflectometer, where arrays of fine slits allow only certain particle trajectories to pass. In the AEgIS setup, the antihydrogen atoms that pass through the slits in the deflectometer will be recorded with a hybrid device: a silicon detector coupled to a high-resolution emulsion detector, which, like a photographic film, takes snapshots of the impact point of antihydrogen atoms when they annihilate with matter. The arrival positions can then be compared to fringes of light produced by the same slits, to calculate the degree of deflection. To test the set-up antiprotons were used instead of antihydrogen, and their deflection measured in a stray electromagnetic field rather than the gravitational field of the Earth. It’s a significant milestone, but with gravity being vastly weaker than electromagnetism, the AEgIS collaboration still has much work to do before they’re ready to see whether gravity influences antimatter in the same way as matter. 

The AEgIS collaboration brings together physicists from 25 institutes in Europe. This demonstration results from the effort of an interdisciplinary and multinational group of physicists, combining techniques from different fields of physics.

Read more: "A moiré deflectometer for antimatter"Nature Communications