While studying cosmic rays in a Wilson cloud chamber, the Soviet academic Dimitri Skobeltsyn noticed something unexpected among the tracks left by high-energy charged particles. Some particles would act like electrons but curve the opposite way in a magnetic field. In an independent experiment that same year, Caltech graduate student Chung-Yao Chao observed the same phenomenon. The results were inconclusive, and both scientists disregarded the anomaly.
First sighting of positron disregarded
Discovering the positron