Antimatter gravity with muonium

• Main Authors: Kaplan, Daniel M, Fischbach, Ephraim, Kirch, Klaus, Mancini, Derrick C, Phillips, James D, Phillips, Thomas J, Reasenberg, Robert D, Roberts, Thomas J, Terry, Jeff
• Format: Journal Article
• Language: English
• Published: 26.01.2016
• Subjects: Physics - General Relativity and Quantum Cosmology; Physics - High Energy Physics - Experiment; Physics - Instrumentation and Detectors
• DOI: 10.48550/arxiv.1601.07222

The gravitational acceleration of antimatter, $\bar{g}$, has never been directly measured and could bear importantly on our understanding of gravity, the possible existence of a fifth force, and the nature and early history of the universe. Three avenues appear feasible for such a measurement: antihydrogen, positronium, and muonium. The muonium measurement requires a novel monoenergetic, low-velocity, horizontal muonium beam directed at an atom interferometer. The precision three-grating interferometer can be produced in silicon nitride or ultrananocrystalline diamond using state-of-the-art nanofabrication. The required precision alignment and calibration at the picometer level also appear to be feasible. With 100 nm grating pitch, a 10% measurement of $\bar{g}$ can be made using some months of surface-muon beam time, and a 1% or better measurement with a correspondingly larger exposure. This could constitute the first gravitational measurement of leptonic matter, of 2nd-generation matter and, possibly, the first measurement of the gravitational acceleration of antimatter.