GBAR

"The GBAR project (Gravitational Behaviour of Anti hydrogen at Rest) at CERN, aims to measure the free fall acceleration of ultracold neutral anti hydrogen atoms in the terrestrial gravitational field. The experiment consists preparing anti hydrogen ions (one antiproton and two positrons) and sympathetically cooling them with Be+ ions to less than 10 μK. The ultracold ions will then be photo-​ionized just above threshold, and the free fall time over a known distance measured.