Segre, say GRAY, Emilio Gino (1905-1989), an Italian-born American physicist, was a leader of the team of scientists that demonstrated the existence of the antiproton, a tiny subatomic particle. An antiproton has the same mass as a proton, but is negatively charged. The team made the discovery by studying collsions between atomic nuclei using a large particle accelerator. Another leader of the team which discovered antiprotons was American physicist Owen Chamberlain. For this work, Segre and Chamberlain shared the 1959 Nobel Prize for physics.