And since hydrogen is electricallyneutral, it should be possible to observe gravity's tiny tug on it without the confounding effects of electrostatic attraction to other particles.
They are looking in particular at how long it takes a B-meson to change its nature, focusing on one particular member of the extended B-meson family, the electricallyneutral B0.
It will examine neutrons (the electricallyneutral components of atomic nuclei) that are ejected from the lunar surface after being bombarded by cosmic rays (energetic particles that constantly streak through space).
Sterile neutrinos differ from ordinary neutrinos (electrically neutral particles produced in abundance by the nuclear reactions that power the sun) because ordinary neutrinos feel the weak nuclear force, while sterile ones do not.
What is useful about neutrons for these experiments is that they are electricallyneutral - within the experiment, they are as isolated from all the forces of nature as they can possibly be, with only gravity to act on them.