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James Cronin (1931-2016)

October 6, 2016

Physicists, perhaps purposely memorializing the Greek philosophers who were the first to contemplate the laws of physics, have had an affinity for using Greek alphabet letters in their equations, and Greek words as descriptors. An early example of this is George Stoney's naming of the electron after the Greek word for electrostatically-charging amber, ηλεκτρον. There's also the famous Alpher–Bethe–Gamow paper, for which George Gamow added Hans Bethe as a co-author with his student, Ralph Alpher, to make an alpha-beta-gamma paper.[1]

Figure caption

A quotation from the first paragraph of Aristotle's Physics. Aristotle (384-322 BC) is depicted to the right of the older Plato (c.425-c.348 BC) in this portion of Raphael's 1509 "The School of Athens" (Left image and Greek text, via Wikimedia Commons. English translation from ref. 2.)[2])

This predilection is most apparent in the names of many of the elementary particles. As shown below, seventeen of the twenty four letters of the classical Greek alphabet have been used.[3]

 Alpha particleRho meson
 Beta particleSigma baryon
 Gamma rayTau lepton
 Delta baryonUpsilon meson
 Eta mesonPhi meson
 Theta mesonXi baryon
 Lambda baryonJ/psi meson
 MuonOmega baryon
 Pi meson (Pion) 

One elementary particle that's not in this list is the kaon, also called the K meson. The kaon proved to be an important particle, since the decay of neutral kaons violates CP symmetry. CP symmetry essentially states that physics should be the same when time is reversed; that is, by playing the "video" of nature backwards.

The important aspect of this CP violation is that it allows the existence of more matter than antimatter in our universe. For their 1964 discovery of CP violation in neutral kaon decay, James Cronin (1931-2016) and Val Fitch (1923-2015) were awarded the 1980 Nobel Prize in Physics. James Cronin died on August 25, 2016, at age 84.[4-7]

James Cronin was born in Chicago on September 29, 1931, to a father, James Farley Cronin, who was a graduate student at the The University of Chicago. His father was a student of classical languages who had met his future wife, Dorothy Watson, in a Greek class at Northwestern University.[4,7]

In September, 1939, his father became a professor of Latin and Greek at Southern Methodist University in Dallas, Texas, where Cronin received his undergraduate education in physics and mathematics.[6-7] Cronin wrote that a high school physics teacher inspired his interest in physics.[7]

After receiving his B.S. degree from Southern Methodist University in 1951, Cronin went to the University of Chicago, where his graduate education involved such professors as Enrico Fermi and Murray Gell-Mann.[6] His thesis under Samuel Allison was in experimental nuclear physics on the spin and parity of the nuclear states of carbon.[5-6] He came away from Chicago with an M.S. (1953), a Ph.D. (1955), and a wife, Annette Martin, who was also a student at Chicago.[4-5] He was a National Science Foundation fellow from 1952-1955.[7]

Cronin had a short stay at Brookhaven National Laboratory (1955-1958), and then became a professor at Princeton University, staying there until 1971.[7] He finished his career as University Professor of Physics at the University of Chicago.[4] His return to Chicago was prompted by the proximity of the Fermi National Accelerator Laboratory (Fermilab) with its 400 GeV particle accelerator.[5,7]

Cronin and Fitch were both Princeton professors when they did their kaon experiment at the Brookhaven National Laboratory Alternating Gradient Synchrotron accelerator.[4,6] In their 1964 experiments, they found that the long-lived neutral kaon decayed into two pions, an unexpected result that violated CP symmetry.[5] Kaons are interesting, since they oscillate between normal kaons and antimatter kaons.[6] Cronin and Fitch discovered that the transition from kaon to anti-kaon occurred slightly less frequently.[6]

Val Fitch, left, and James Cronin, right

James Cronin, right, with Val Fitch.

Cronin and Fitch were awarded the 1980 Nobel Prize in Physics "for the discovery of violations of fundamental symmetry principles in the decay of neutral K-mesons."

(US Department of Energy photo via Wikimedia Commons.)

Since the effect was small, there was initial skepticism of the result, but confirming experiments in other laboratories showed that the effect was real.[6] This experiment showed why a Big Bang universe could contain just normal matter, and not a mixture of matter and antimatter. Antimatter would decay slightly faster, leaving just normal matter behind.[6]

Cronin was named head of the Fermilab Colliding Beams Division in 1977, a position he held for just a few months before he realized that he enjoyed being a scientist, not an administrator.[5] In 1982, he measured the pion lifetime at CERN.[5] After that, the age of small particle physics experiments was over, the field becoming dominated by huge research teams, and Cronin migrated to cosmic ray studies.[5]

Cronin helped to start the Pierre Auger Project, an international collaboration to investigate cosmic rays and their sources.[4,6] This project sited an array of more than a thousand cosmic ray detectors covering 3,000 square kilometers in Argentina to create the Auger Observatory.[4,5] The James Cronin School, a high school in Malargüe, Argentina, was established through donations by Cronin and private donors.[5]

Cronin was a member of the American Physical Society, the National Academy of Sciences, a foreign member of the Royal Society of London and the French Legion d'honneur.[4] He was awarded the National Medal of Science in 1999, the Ernest Orlando Lawrence Memorial Award for outstanding contributions in the field of atomic energy in 1977, and the John Price Wetherill Medal of the Franklin Institute in 1975.[4]

Edward Kolb, Dean of the Physical Sciences Division of the University of Chicago, said this or Cronin:
"Just like in basketball, there are good players in science, but the greatest players are the ones who make the people around them better. Jim was that great player."[4]
Among his survivors are six grandchildren.[4] One interesting fact is that Cronin did his own data analysis using fortran, called FORTRAN in those early days.[5]


  1. R. A. Alpher, H. Bethe, and G. Gamow, "The Origin of Chemical Elements," Phys. Rev. vol. 73, no. 7 (April 1, 1948), pp. 803f.,http://dx.doi.org/10.1103/PhysRev.73.803.
  2. Aristotle, "Physics," R. P. Hardie and R. K. Gaye, Trans., on the Internet Classics Archive by Daniel C. Stevenson. Also at greek-texts.com.
  3. There are Greek letters other than these twenty four. One example is the digamma (ϝ), pronounced as waw, or wau, and used as the /w/ sound. Its most common use was as the numeral, six, where it was often written as a final sigma character, ς.
  4. Steve Koppes, "James W. Cronin, Nobel laureate and pioneering physicist, 1931-2016," University of Chicago Press Release, August 27, 2016.
  5. Alan Watson, "Obituary - James Cronin (1931–2016), Nature, vol. 537, no. 7621 (September 21, 2016), p. 489, doi:10.1038/537489a.
  6. James Cronin, Nobel Prize winner in Physics – obituary, Telegraph (UK), August 30, 2016.
  7. James Cronin - Biographical, From Les Prix Nobel, The Nobel Prizes 1980, Wilhelm Odelberg, Ed., (Nobel Foundation, Stockholm, 1981).

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