(1922–) American physicist
The son of Russian immigrants, Lederman was born in New York and educated at City College there. After three years with the US Signal Corps during the war, he went to Columbia where he gained his PhD in 1951. He was appointed professor of physics in 1958 and remained at Columbia until 1979, when he accepted the directorship of the Fermi National Accelerator Laboratory, Batavia, Illinois, a post he held until his retirement in 1989.
In 1959 T. D. Lee asked his Columbia colleagues Lederman, Melvin Schwartz (1932– ), and Jack Steinberger (1921– ) if it was possible to study the weak fundamental interaction at high energies. While well understood at low energies, Lee noted, theories of weak interactions at high energies led to absurdities. Yet it was difficult to explore the interaction experimentally, for at high energies other forces tended to obscure all other reactions.
Lederman and his coworkers began to investigate decay processes that lead to neutrinos. These proceed by a weak interaction, and there are two processes in which they can occur. In one, pions decay to give muons and neutrinos. The other, beta decay, is decay of a neutron to give a proton, an electron, and a neutrino.
In what has become known as the two-neutrino experiment, the team investigated the question of whether the two types of neutrino were identical – whether the muon neutrino was the same particle as the electron neutrino. The experiment was difficult since neutrinos have a very low probability of interacting with matter. It required an intense beam of high-energy neutrinos and a large detector to have any chance of yielding a measurable number of events.
Using the Alternating Gradient Synchrotron at Brookhaven, a beam of 1011 protons per second were directed with an energy of 30 billion electronvolts (30 GeV) at a beryllium target. This produced a large number of pions, which rapidly decay into muons and neutrinos. The muons were filtered out by a steel barrier 44-feet thick built from the plates of an old battleship. The neutrinos passed through untouched into a ten-ton aluminum detector. The experiment ran for ten days and diverted 1014 high-energy neutrinos through the detector. If there was only one type of neutrino it should react in the experiment with neutrons to produce an equal number of muons and electrons; if, however, the experiment produced a unique muon-linked neutrino, only muons should be created. Fifty-one neutrino collisions were recorded by the detector; all produced muons and none an electron.
For this work Lederman and his Columbia colleagues Schwartz and Steinberger shared the 1988 Nobel Prize for physics.
In 1977 Lederman led another team that made a second fundamental discovery. Working with the Fermilab accelerator they discovered a new particle nine times heavier than the proton. It was named the upsilon particle and provided the first evidence of the fifth quark – the so-called ‘bottom quark’. Lederman has given a popular account of particle physics in his 1992 book The God Particle (the title refers to the Higgs boson).
Subjects: Science and Mathematics.