In Memoriam: Preeminent Yale Physicist Vernon W. Hughes, Who Was a Leader in Experimental Particle Physics

Vernon W. Hughes, Sterling Professor Emeritus at Yale University, and elementary particle physicist, died on March 25 in New Haven at age 82.

Hughes’ career involved a broad spectrum of studies of physical phenomena ranging from very low to very high energy. His work consistently maintained the theme of understanding the physics of elementary particles and their interactions at the most fundamental level.

During World War II, he helped develop radar at the MIT Radiation Laboratory and was one of the co-editors of a volume of the Radiation Laboratory Series titled “Waveforms,” a contribution that has been of major significance to the development of the American electronics industry.

“He was never satisfied until he fully understood whatever phenomenon he studied,” said D. Allan Bromley, Sterling Professor of the Sciences at Yale. “Hughes educated a generation of students who have become leaders in the international scientific community. He will be much missed worldwide by all his friends and collaborators, most especially by his colleagues at Yale who admired his endless supply of energy, drive and unyielding persistence.”

Hughes conducted extensive studies of the simple positronium atom (a hydrogen-like atom consisting of a positive and negative electron pair) and helium (an atom with two electrons).

One area for which Hughes is particularly well known is the study of atomic and particle physics using experiments with muonium, the atom formed by an electron bound to an elementary particle called the muon. Hughes made the first observation of this fundamental atom in 1960. His experiments evolved with precision measurements of the influences of magnetic fields on the atom, led to an improved measurement of the magnetic properties on the muon, and matured to extremely precise measurements.

These 35 years of experimentation verified to high precision that the muon is a “heavy electron” and provided new avenues into the experimental study of quantum electrodynamics. This also created a tool to probe the highest energy scales of elementary particle physics.

Hughes originated the use of polarized electrons in high-energy accelerators- another field of great importance. In the more common unpolarized beams, the individual electrons spin around themselves-as the Earth does every 24 hours- around axes of rotation that are randomly oriented. In a polarized beam they preferentially point in one direction. The existence of this preferred direction then allows for a whole new array of possible measurements.

Hughes’ interest in polarized electron beams began in 1959; and he developed the first polarized source for the Stanford two-mile accelerator. His vision and perseverance led to the first measurements of the internal structure of the proton that revealed not only the particles within, but also their spin, and to the historic observation of parity non-conservation (the fact that nature distinguishes between an experiment and its mirror image). The recent successes of the Stanford Linear collider experiments are directly traceable to Hughes’ seminal work.

Hughes’ pioneering work also opened the field of nuclear physics to investigations with polarized electrons at low energy accelerators. He and collaborators at the Bates Linear Accelerator performed the first such experiment in this country that observed parity violation in polarized electron-Carbon elastic scattering.

Extending the reach of deep inelastic polarized lepton scattering from nucleons, Hughes led a large collaboration at the European accelerator in Geneva, Switzerland, in investigations in employing polarized muons scattering from polarized neutrons and protons. This work was stimulated by the “proton spin crisis” first observed by Hughes and his group, and led to more complete understanding of the relationship between the nature of the constituents of the proton and its spin.

Most recently, Hughes conceived of and led an experiment at Brookhaven National Laboratory to greatly improve the measurement of magnetic properties of the muon. This quantity embodies our knowledge of the interactions of elementary particles in one parameter. It has long served as crucial parameter with which we can test new ideas in particle physics.

Born in Kankakee, Illinois on May 28, 1921, he attended Columbia University, where he received a master’s degree in 1941 and a Ph.D. in 1950. His sponsor was the Nobel Prize winning physicist, I.I. Rabi. His thesis, which he worked on with L. Grabner, observed for the first time a phenomenon involving the interaction of light with molecules. Hughes’ work was a pioneering investigation of effects, which are important factors in modern laser studies of the properties of light and matter.

Hughes was on the Yale faculty from 1954 until his retirement in 1991. He was Sterling Professor, the highest honor that Yale can bestow. He was chair of the physics department there from 1961 to 1966 and presided over a large expansion of the department. His many honors include membership in the National Academy of Sciences, an honorary doctorate from the University of Heidelberg, and both the Davisson-Germer Prize in Atomic Physics and the Tom R. Bonner Prize in Nuclear Physics of the American Physical Society.

Hughes’ focus was always on the most fundamental questions in physics. His development of ultra precise experimental techniques allowed him to establish several of the fundamental constants characterizing the highly diverse universe and its phenomena, with unprecedented precision.

Vernon Hughes was predeceased by his first wife, Inge, and is survived by his second wife, Miriam, and two sons, Gareth of Albuquerque, New Mexico; and Emlyn of Pasadena, California; and four grandchildren, Ariel, Isaac, Noah and Inge Jovana.

Contributions towards a fellowship for graduate students in Hughes’ name may be sent to Ramamurti Shankar, chair of Physics Department. P.O. Box 208120, New Haven, Conn. 06520-8120.

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