Antimatter & gravitation

Antimatter & gravitation

Scheme of the GBAR experiment. Figure from P. Pérez and Y. Sacquin, Class. Quantum Grav. 29, 184008 (2012).
Scheme of the GBAR experiment. Figure from P. Pérez and Y. Sacquin, Class. Quantum Grav. 29, 184008 (2012).

There is no measurement of the free fall of antimatter in the gravitational field of the Earth. More generally there is no direct test of the Equivalence Principle with antimatter. The GBAR experiment at CERN is a direct measurement of g for antimatter with a first sensitivity objective of 0.1%.

The experiment aims at measuring the free fall acceleration of neutral antihydrogen atoms. The originality of GBAR is to first produce the H+ ion. This ion can then be cooled down to μK temperatures (i.e. m/s velocities). The excess positron can then be laser detached in order to recover the neutral H atom. This process can be set up to minimize momentum transfer in the vertical direction.

GBAR is installed at the ELENA low-energy ring of CERN that produced antiproton bunches of 100 keV. These antiprotons entering the GBAR experiment and then further cooled down to the keV level. The last stage of the cooling is done in a trap through collisions with trapped electrons.

We foressee to contribute in the near future to GBAR at the stage of the antiproton cooling phase. We intend to propose to design a recirculation of the antiprotons within the experiment that could, in the near future, enhance significantly the luminosity of the experiment.