Abstract
The gravitational acceleration of antimatter, g ¯ , has yet to be directly measured; an unexpected outcome of its measurement could change our understanding of gravity, the universe, and the possibility of a fifth force. Three avenues are apparent for such a measurement: antihydrogen, positronium, and muonium, the last requiring a precision atom interferometer and novel muonium beam under development. The interferometer and its few-picometer alignment and calibration systems appear feasible. With 100 nm grating pitch, measurements of g ¯ to 10%, 1%, or better can be envisioned. These could constitute the first gravitational measurements of leptonic matter, of 2nd-generation matter, and possibly, of antimatter.
Highlights
The question of antimatter gravity, first raised in the 1950s [1], is of continuing interest [2,3].To date, decades of experimental effort have yet to yield a statistically significant direct measurement.Antimatter gravity studies using antihydrogen are ongoing [4,5,6,7], and experiments with positronium have been discussed [8]
We report here on progress towards a measurement with muonium (Mu), an exotic atom consisting of an electron bound to an antimuon
The most sensitive limits on antimatter gravity currently come from indirect tests, relying on the expected amounts of virtual antimatter in the nuclei of various elements
Summary
The question of antimatter gravity, first raised in the 1950s [1], is of continuing interest [2,3]. A direct test of the gravitational interaction of antimatter with matter is desirable on quite general grounds [2].2 Such a measurement can be viewed as a test of general relativity or as a search for a fifth force and is of interest from both perspectives. The slower initial expansion allows the visible universe to be in thermal contact, resolving the horizon problem with no need for inflation [38,41], and the age problem with no need for dark energy [38] Having both positive and negative gravitational mass results in gravitational vacuum polarization [36,49], which provides a mechanism for Modified. On antimatter gravity even for antihydrogen. The forgoing considerations provide more than sufficient motivation (especially given the relatively modest level of experimental effort and expense required) for a measurement of muonium gravity to be pursued
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