The PS210 experiment was the first experiment that led to the observation of antihydrogen atoms produced at the Low Energy Antiproton Ring (LEAR) at CERN in 1995.^[1] The antihydrogen atoms were produced in flight and moved at nearly the speed of light.^[2] They made unique electrical signals in detectors that destroyed them almost immediately after they formed by matter–antimatter annihilation.^[3]

Eleven signals were observed, of which two were attributed to other processes.^[1] In 1997 similar observations were announced at Fermilab from the E862 experiment.^[4] The first measurement demonstrated the existence of antihydrogen,^[1] the second (with improved setup and intensity monitoring) measured the production rate.^[4] Both experiments, one at each of the only two facilities with suitable antiprotons, were stimulated by calculations which suggested the possibility of making very fast antihydrogen within existing circular accelerators.