GBAR experiment

GBAR (Gravitational Behaviour of Anti hydrogen at Rest), AD-7 experiment, is a multinational collaboration at the Antiproton Decelerator of CERN.

The GBAR project aims to measure the free-fall acceleration of ultra-cold neutral anti-hydrogen atoms in the terrestrial gravitational field.

The equivalence principle says that the gravitational force on a particle is independent of its internal structure and composition.

The ultra-cold ions are then photoionized just above the threshold using a laser pulse; this removes the outermost positron and forms neutral anti-hydrogen.

In theory, the electrically neutral antineutrons would be the smallest chunks for this experiment, but they cannot be used to due their quick decay time.