Precision atomic physics measurements with antimatter may help us understand the lingering Baryon asymmetry problem. The ALPHA Collaboration has recently published the first direct measurements of the gravitational effect on the trajectory of antiparticles in ALPHA-g, an apparatus dedicated to making measurements on antimatter gravitation [1]. This first-of-a-kind direct test of the free-fall Weak Equivalence Principle definitively measures the effect of gravitational acceleration on antimatter. With a best-fit value of the effective gravitational acceleration of antihydrogen of (0.75 ± 0.13 (stat. + syst.) ± 0.16 (simulation)), it finds consequent motion of antimatter consistent with that expected of matter. We present a brief background of this effort in the context of experiments conducted to date at ALPHA and explain the underlying principle of the magnetic bias technique used to probe the gravitational behaviour of the anti-atoms in our trap. We explain the experimental techniques used to realize the measurement and present the experimental results and analysis in detail. Finally, we outline the future direction of gravitation measurements on ALPHA-g.
[1] Anderson, E.K., et al. (ALPHA Collaboration) Observation of the effect of gravity on the motion of antimatter. Nature 621, 716–722 (2023). https://doi.org/10.1038/s41586-023-06527-1