First measurement of the antihydrogen production cross section through the charge-exchange reaction of low-energy antiprotons with orthopositronium

The GBAR experiment has measured the formation rate of antihydrogen from antiproton impact on a positronium cloud for antiproton kinetic energies of 4 and 6 keV. This is the first charge-exchange cross section measurement performed using antiproton beams, which are provided by the AD-ELENA facility at CERN. The measured cross section values are (14.1 ± 1.3 (stat) +2.2-1.4 (sys)) × 10⁻¹⁶~cm² at 6.2 keV energy and (8.7 ± 2.4 (stat) +1.5-0.09 (sys)) × 10⁻¹⁶~cm² at 4.15 keV energy, and agree with recent theoretical three-body calculations for antihydrogen formation. These measurements are an important input for experiments with antimatter, e.g the planned measurements of antihydrogen gravitational acceleration in the GBAR collaboration.