Solid confirmation for the discovery of the antiproton came shortly after its first detection in September 1955, through the visual evidence offered by the observation of annihilation stars in nuclear emulsions exposed to the Bevatron beam. The emulsion work was a result of a cooperative effort between Emilio Segrè's team in Berkeley and the group of physicists working under the guidance of Edoardo Amaldi in Rome, who had already observed a possible antiproton annihilation star in emulsions exposed to cosmic rays. The origin and development of the Rome-Berkeley collaboration are presented, in the wider context of the changing balance between cosmic ray investigation and accelerator research in the mid-fifties.