Scientists have reported a new way to produce a controlled beam of muonium, an exotic atom made of a muon and an electron. Muons are heavier cousins of electrons, and muonium behaves somewhat like a hydrogen atom but with the proton replaced by a muon. The advance is described in a recent ScienceDaily release.
The key significance is that this beam could allow researchers to test, for the first time, whether gravity acts on second-generation particles exactly as Einstein's theory of general relativity predicts. Until now, such a test was not feasible because muonium is difficult to create and control in sufficient quantities.
The source does not provide details on the experimental setup or timeline, but it states that the controlled beam is a crucial step. No other sources are cited, so there is no independent confirmation or differing viewpoint to compare.