[1][2] Remaining in Italy during World War II, he did fundamental research under difficult conditions in the basement of a high school, which first clarified the nature of the muon.

[3] In 1946 he emigrated to the United States, where he worked first at the Massachusetts Institute of Technology with Bruno Rossi, and then at Brookhaven National Laboratory's Cosmotron, developing faster nuclear electronics and essential techniques for extracting, transporting, and focusing beams of high energy particles.

His important contributions to the design of the experiment that discovered the antiproton in 1955 were acknowledged in the 1959 ceremony in which the Nobel Prize in Physics was awarded to Emilio Segrè and Owen Chamberlain.

[4] Unfortunately a famous quarrel over credit and priority for the discovery embittered Piccioni for much of his later life, to the point that he filed a lawsuit in 1972 against Segrè and Chamberlain, seeking damages and public acknowledgment of his contributions.

[7][8] Piccioni retired from UCSD as Professor Emeritus in 1986, but continued to give review talks and work in the investigation of fundamental problems in quantum mechanics.