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

Abstract

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 $(14.1\pm 1.3{(\mathrm{stat})}_{-1.4}^{+2.2}(\mathrm{sys}))\times 10^{-16}$~cm${}^2$ at 6.2 keV energy and $(8.7\pm 2.4{(\mathrm{stat})}_{-0.09}^{+1.5}(\mathrm{sys}))\times 10^{-16}$~cm${}^2$ 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.