Perl, Martin Lewis, 1927–, American physicist, b. New York City, Ph.D. Columbia, 1955. He was a professor at the Univ. of Michigan from 1955 to 1963, when he accepted a position at Stanford; he retired as professor emeritus there in 2004. Perl and Frederick Reines were jointly awarded the 1995 Nobel Prize in Physics for pioneering experimental contributions to lepton physics. Perl discovered (1975) the tau lepton, a subatomic particle that is similar to the electron but 3,500 times heavier and far less stable. Until Perl's discovery, there were only two known families of elementary building blocks in the standard model of particle physics; the tau lepton turned out to be the first-discovered member of a third family.