The award citation credits Willis "For his leading role in the development and exploitation of innovative techniques now widely adopted in particle physics, including liquid argon calorimetry, electron identification by detection of transition radiation, and hyperon beams." "These techniques were developed with colleagues at Brookhaven, and I am grateful for the Lab's support of these unusual ideas," said Willis.
In the 1960s, physicists measured the energy of high-energy particles by absorbing radiation inside a large block of steel, an instrument called a calorimeter. In the 1970s, Willis saw the need to measure the energy flow of all the particles from new colliding beam accelerators to find the origin of weak interactions, one of the four forces of nature. Willis, with Brookhaven Lab's Instrumentation Division Head Veljko Radeka, divided the block of steel into many pieces and filled gaps in it with liquid argon to detect radiation, which is transformed into electrical current in the liquid argon. First used at Brookhaven's accelerator, the Alternating Gradient Synchrotron (AGS), liquid argon calorimetry is now used in many of the world's accelerators.
In 1973, Willis, along with Radeka and Brookhaven physicist Robert Palmer, developed electron identification by detection of transition radiation. The technique uses 1,000 sheets of precisely spaced lithium for measuring x-rays in physics experiments. The innovation made possible measurements at higher energies than with other techniques.
The strange version of the nucleon with negative charge, the sigma minus hyperon, was discovered at Brookhaven in 1953. The particle decayed after traveling about an inch, allowing its study only in detectors like the cloud chamber used in the discovery. Einstein predicted that the decay time for a fast-moving particle would be slower than for a slow-moving particle. In the early 1970s, Willis proposed to take advantage of this effect to create an actual beam of hyperons, using the high energy of the AGS.
Willis earned a B.S. and Ph.D. in physics from Yale University, in 1954 and 1958, respectively. He joined Brookhaven Lab as an assistant physicist in 1958. He moved on to Yale in 1965, where he joined the physics faculty. From 1964 to 1983, he retained an appointment as guest physicist at Brookhaven. He joined CERN, the European physics laboratory, in 1973, and he moved to Columbia University to become Eugene Higgins Professor of Physics in 1990. In the same year, he was appointed a senior physicist at Brookhaven. He is currently project manager for the U.S. ATLAS collaboration, working with the ATLAS experiment at the CERN Large Hadron Collider.
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