Superfluid helium "atomic cannon" fires muonium beam for gravity test

Researchers at ETH Zurich and PSI have produced a controlled beam of muonium, an atom made of an electron and an antimuon, using superfluid helium cooled to near absolute zero. The advance clears a key obstacle to measuring how gravity acts on a second-generation particle and testing Einstein's equivalence principle; the actual gravity experiment is expected in two to three years.

• Muonium is formed in superfluid helium at about −273 °C
• Chemical potential launches atoms vertically out of the liquid like a cannon
• Muons decay after just 2.2 microseconds on average, limiting the experiment
• First beam test expected this year, gravity measurement in 2–3 years