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Isotopic spin (Part 2)

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Isotopic spin (Part 1)
Murray Gell-Mann Scientist
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In Chicago–I naturally made certain assumptions. One was that there was a difference between baryons and-well, no, let me start differently. One was that there were various interactions: there was gravitation; there was electromagnetism; there was a weak interaction giving rise to beta decay, mu decay, mu absorption and strange analogues of beta decay and mu absorption. And then there was the strong interaction. And certain particles participated in the strong interaction–like pions and nucleons–and others did not–like muons and electrons and neutrinos. Then isotopic spin was presumably applicable to the strongly interacting particles, and the pion had isotopic spin I and the nucleon had isotopic spin one half, and isotopic spin was approximately conserved but its conservation was broken by electromagnetism because the electromagnetic current had a portion of it which was isotopic spin I and a portion that was isotopic spin zero. So in the emission of a photon you could either conserve isotopic spin or change it by a unit. In the emission of–emission and absorption of–a virtual photon you could violate isotopic spin conservation. That isotopic spin was a good concept for both pions and nucleons was being shown in our own laboratory in the experiments of Fermi and his collaborators. So it naturally occurred to me that isotopic spin might have something to do with the strange particles. The strange particles might be strongly interacting particles participating in the strong interaction, produced copiously because they were strongly interacting–but inhibited from decay, from rapid…  but prevented from decaying rapidly by a conservation law, which was however slightly broken so that they could actually finally decay, but slowly. And I thought maybe isotopic spin was this conservation law that would prevent them from decaying rapidly. Then a strange particle might for example have isotopic spin five halves, if it had only enough energy to decay into a nucleon and one pion–but not two–then isotopic spin would prevent its decay into nucleon plus one pion. But–and here's the catch–electromagnetism would violate the conservation of isotopic spin and then permit it after all to decay–a little bit more slowly into nucleon plus pion, but only a little bit more slowly because electromagnetism is not that weak. So when I proposed this idea and we discussed it in our theory group at Caltech, it became clear that...well, I just discussed it with Goldberger and Adams, not with anyone else; not with Enrico, just with Goldberger and Adams. It was clear that the idea by itself wouldn't work.

New York-born physicist Murray Gell-Mann (1929-2019) was known for his creation of the eightfold way, an ordering system for subatomic particles, comparable to the periodic table. His discovery of the omega-minus particle filled a gap in the system, brought the theory wide acceptance and led to Gell-Mann's winning the Nobel Prize in Physics in 1969.

Listeners: Geoffrey West

Geoffrey West is a Staff Member, Fellow, and Program Manager for High Energy Physics at Los Alamos National Laboratory. He is also a member of The Santa Fe Institute. He is a native of England and was educated at Cambridge University (B.A. 1961). He received his Ph.D. from Stanford University in 1966 followed by post-doctoral appointments at Cornell and Harvard Universities. He returned to Stanford as a faculty member in 1970. He left to build and lead the Theoretical High Energy Physics Group at Los Alamos. He has numerous scientific publications including the editing of three books. His primary interest has been in fundamental questions in Physics, especially those concerning the elementary particles and their interactions. His long-term fascination in general scaling phenomena grew out of his work on scaling in quantum chromodynamics and the unification of all forces of nature. In 1996 this evolved into the highly productive collaboration with James Brown and Brian Enquist on the origin of allometric scaling laws in biology and the development of realistic quantitative models that analyse the influence of size on the structural and functional design of organisms.

Tags: University of Chicago, Institute of Nuclear Studies, Caltech, Enrico Fermi, Murph Goldberger, Ed Adams

Duration: 3 minutes, 38 seconds

Date story recorded: October 1997

Date story went live: 24 January 2008