Abstract
The weak equivalence principle states that the motion of a body in a gravitational field is independent of its structure or composition. This postulate of general relativity has been tested to very high precision with ordinary matter, but no relevant experimental verification with antimatter has ever been carried out. The AEGIS experiment will measure the gravitational acceleration of antihydrogen to ultimately 1% precision. For this purpose, a pulsed horizontal antihydrogen beam with a velocity of several 100 m s−1 will be produced. Its vertical deflection due to gravity will be detected by a setup consisting of material gratings coupled with a position-sensitive detector, operating as a moire deflectometer or an atom interferometer. The AEGIS experiment is installed at CERN’s Antiproton Decelerator, currently the only facility in the world which produces copious amounts of low-energy antiprotons. The construction of the setup has been going on since 2010 and is nearing completion. A proof-of-principle experiment with antiprotons has demonstrated that the deflection of antiparticles by a few μm due to an external force can be detected. Technological and scientific development pertaining to specific challenges of the experiment, such as antihydrogen formation by positronium charge exchange or the position-sensitive detection of antihydrogen annihilations, is ongoing.
Highlights
The study of antimatter in the laboratory has the potential to elucidate one of the great unsolved questions in physics: Why does the observable universe appear to contain only ordinary baryonic matter and no sizable amounts of antimatter? In order to solve the baryon asymmetry riddle, several experiments at CERN’s Antiproton Decelerator (AD) [1] are studying antihydrogen (H), the simplest atomic antimatter system
The weak equivalence principle states that the motion of a body in a gravitational field is independent of its structure or composition
As a prerequisite for the use of the novel excitation scheme, we studied the structure of Ps by single-shot positronium annihilation lifetime spectroscopy (SSPALS) [36]
Summary
The study of antimatter in the laboratory has the potential to elucidate one of the great unsolved questions in physics: Why does the observable universe appear to contain only ordinary baryonic matter and no sizable amounts of antimatter? In order to solve the baryon asymmetry riddle, several experiments at CERN’s Antiproton Decelerator (AD) [1] are studying antihydrogen (H), the simplest atomic antimatter system. While the WEP has been tested up to a relative precision of 1.8 × 10−13 with ordinary matter [10], no relevant measurement of the gravitational acceleration of antimatter has been carried out This is because until recently only electrically charged antimatter particles – such as positrons (e+) and antiprotons (p) – were readily available, which are too sensitive to stray electromagnetic fields to permit a gravity measurement [11]. This situation changed in 2002, when copious amounts of cold H were synthesized for the first time by the ATHENA experiment [12] installed at the AD. In combination with an efficient cooling technique for p, this scheme can create ultracold H for high-precision gravity measurements
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