This original 1930 cloud-chamber photograph by Carl Anderson shows the track of a positively charged particle (thin track curving to the left) of electronic mass slowed down by passing upward through a lead plate (horizontal thick line). Image Copyright © Lawrence Berkeley Laboratory

In 1932, Carl Anderson, a US physicist, while examining tracks of particles produced by cosmic rays, noticed one track whose curvature was identical to that of an electron but was flipped. Instead of curving to the right, it curved to the left. He named this positively charged electron a positron, the first antimatter particle discovered. Many anti-particles have been discovered since. The anti-proton was discovered in 1955 by E. Segre and his coworkers at the Lawrence Berkeley Laboratory using a high-energy particle accelerator. Most other anti-particles have been discovered at particle accelerators under carefully designed conditions. Many experimental groups have also reported constructing bigger entities than just anti-particles. In fact, whole anti-nuclei have been constructed, for example anti-hydrogen nuclei and an isotope of anti-helium.

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