First application of a Moiré deflectometer in antimatter physics

The AEgIS collaboration at CERN (an international consortium of 25 institutions) has demonstrated a method to measure a very small deflection (smaller than the thickness of a human hair) of a beam of antiprotons, the counterpart of the proton.

Figure 1 left: Principle of the moiré deflectometer. The antiprotons enter from the left, traverse the moiré deflectometer consisting of two identical gratings and annihilate in the emulsion detector.Right: Observed shift of the moiré pattern under the influence of a force (from 241 annihilations). Figure 2: Typical antiproton annihilation observed by the emulsion detector.

 This is achieved by putting arrays of fine slits inside the beam (uppermost figure), allowing only certain trajectories to pass these obstacles and to hit a detector.

The arrival point of the surviving antiprotons is recorded with an emulsion detector, in principal a photographic film that takes snap-shots of the antiprotons’ annihilation – the process in which antimatter meets matter and subsequently decomposes into smaller particles. An example of such an “annihilation star” can be seen in the middle figure.

These arrival positions are then compared to fringes of light (see lowermost figure) – making it possible to determine the force that deflected the antiprotons. It is interesting, that this method called morié deflectometry only needs very few particles to work and is therefore ideal for rare particles such as antimatter.

This demonstration results from the effort of an interdisciplinary and multinational group of physicists, combining techniques from different fields of physics. In future experiments, this method could be employed to measure gravity of antihydrogen, a force that is even much smaller than the electromagnetic force measured here.