Figure 3: Energy deposition by atoms and estimated number of atoms.

(a) Distributions of energy deposition in the BGO scintillator for the double coincidence condition (see the text). The distributions are normalized to one mixing cycle of 150 s. The unshaded histogram bordered by the thick blue line is obtained from scheme 1. The total data accumulation time was 4,950 s. The shaded histogram represents data obtained from the background runs, in a total time of 1,550 s. A clear difference is seen at energies higher than 40 MeV, indicating the observation of antihydrogen atoms. (b) The number of integrated events as a function of threshold energy, E_th, after subtraction of the background events. Filled squares are for scheme 1, filled triangles for scheme 2. Errors are propagated from the s.d. of the observed event numbers. (c) The estimated number of antihydrogen atoms that reached the BGO scintillator. The numbers are evaluated by calibrating the counts shown in b with the detection probability as a function of E_th predicted by GEANT4 simulation.