- Email: [email protected]
The 2011 Benjamin Franklin Medal in Physics presented to Nicola Cabibbo
Available online at www.sciencedirect.com
Journal of the Franklin Institute 351 (2014) 117–120 www.elsevier.com/locate/jfranklin
The 2011 Benjamin Franklin Medal in Physics presented to Nicola Cabibbo Gino Segre n Department of Physics and Astronomy, University of Pennsylvania, PA, USA Received 6 June 2012; received in revised form 6 June 2012; accepted 6 June 2012 Available online 11 January 2013
Abstract The Franklin Institute of Philadelphia awards the 2011 Benjamin Franklin Medal in Physics to Nicola Cabibbo for his pioneering work in the field of elementary particle physics, with special emphasis on his role in furthering our understanding of the underlying symmetries that relate one elementary particle interaction to another. Cabibbo, who tragically died in Rome on the 16th of August, 2010, was one of the most brilliant theoretical physicists of the post-World War II period, universally known in the world of physics for his theory describing the decay by weak interactions of particles containing the quantum property known as strangeness. In more than 200 published papers, Cabibbo also made fundamental contributions to other areas of elementary particle physics, including descriptions of electron–positron scattering, the development and application of supercomputers for calculations of quark interactions, and the theory of neutrino oscillations. & 2013 The Franklin Institute. Published by Elsevier Ltd. All rights reserved.
1. Introduction The field of elementary particle physics came into existence as a separate subfield of physics during the 1950s with the building of the accelerators that propelled particles toward either a fixed target or toward each other, the latter being the case in colliding beam accelerators. During this era’s initial phase, a plethora of particles was discovered, many carrying the new quantum number known as strangeness. More massive than the already n
Tel.: þ1 215 247 9453. E-mail address: [email protected]
0016-0032/$32.00 & 2013 The Franklin Institute. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jfranklin.2012.06.011
118
G. Segre / Journal of the Franklin Institute 351 (2014) 117–120
known neutron, proton, and pi meson, the new particles were seen to decay rapidly into lower mass states composed of the former mentioned particles. There were in fact so many new particles being discovered that serious attempts were made to find underlying symmetries that related them to one another in a meaningful way. The most successful effort along these lines was made by Murray Gell-Mann, who proposed in 1961 the existence of the SU(3) symmetry, alternatively known as either the unitary symmetry or as ‘‘The Eightfold Way.’’ His achievement was recognized with The Franklin Institute’s Franklin Medal in 1967 and with the Nobel Prize in 1969. But many problems remained in 1961 in applying the notion of this symmetry to both strongly interacting particles, known as hadrons, and to leptons, particles that have no strong interactions. This is where Cabibbo entered the scene. His paper ‘‘Unitary Symmetry and Leptonic Decays’’, appearing in Physical Review Letters in the summer of 1963, was a watershed in the theory of elementary particles and a key component in establishing what has come to be known as the ‘‘Standard Model of Elementary Particles’’. It remains the most cited paper of the more than 350,000 published by the American Physical Society since 1893. Cabibbo’s singular achievement is most easily understood in the language of quarks, a concept not yet developed at the time of his proposal. This holds that all strongly interacting particles, hadrons, are composed of elementary constituents, quarks, that appear in six varieties: up, down, strange, charm, top, and bottom. They are matched by six leptons—three kinds of neutrinos and electron, muon, and tau. Cabibbo’s work originated from a need to explain two observed phenomena: (1) the transitions between up and down quarks, as well as those between electrons, muons and their companion neutrinos, had similar likelihood of occurring (similar amplitudes) and (2) the transitions with change in strangeness had amplitudes equal approximately to onefourth of those with no change in strangeness. Cabibbo solved the first issue by extending the notion of weak universality, which involves a similarity in the weak interaction coupling strength between different generations of particles. He solved the second issue by invoking a mixing angle yC (now called the Cabibbo angle) in the coupling between the down and strange quarks. Measurements confirmed his hypothesis; the present experimentally determined value of yC is approximately 131. Though Cabibbo’s theory, based on symmetry arguments, was not formulated in terms of quarks, its extension to them was both simple and natural. In 1970, Sheldon Glashow, John Iliopoulos, and Luciano Maiani showed that the rarity of double-strangeness-changing events could be explained in the framework of Cabibbo’s theory by the existence of a fourth (charmed) quark. In 1973, Makoto Kobayashi and Toshihide Maskawa displayed how the extension to a six-quark model could explain the presence of CP (the combination of charge symmetry and parity) violations in weak interactions. This led to a formulation of the 3 3 complex matrix describing the weak interaction decays of all six quarks, a quantity that has been intensively studied both theoretically and experimentally ever since. Known as the CKM or Cabibbo– Kobayashi–Maskawa matrix, it remains a cornerstone of modern elementary particle physics. It had generally been assumed that the three CKM authors would receive the Physics Nobel Prize, so there was a good deal of surprise when it was announced that the 2008 Prize would be awarded half to Yoichiro Nambu and the other half to be shared by Kobayashi and Maskawa. This was particularly true since many felt that the key insight that led to the CKM matrix’s formulation was Cabibbo’s, but in his usual gentlemanly fashion, he refused to be critical of the judgment that had been made.
G. Segre / Journal of the Franklin Institute 351 (2014) 117–120
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Born in Rome in 1935, Cabibbo graduated from the University of Rome I (‘‘La Sapienza’’) in 1958 after completing a thesis on weak interactions under Bruno Touschek. He then went to the Frascati National Laboratories, where he worked with Raoul Gatto on a comprehensive study of electron–positron interactions; that work had a decisive role in shaping research with colliding-beam accelerators. Cabibbo became a full professor in 1965 at the University of L’Aquila, he moved to Rome’s La Sapienza, where he taught from 1966 to 1981; to the University of Rome II (‘‘Tor Vergata’’), where he was a professor from 1981 to 1993; and then back to La Sapienza, where he taught until 2010. He spent considerable time abroad, both in the United States and Europe, during his formative years, but always returned to Rome. Though his influence on physics was enormous, it was particularly strongly felt in Italy. The very well known theoretical physicist Giorgio Parisi (among many honors, one of the few foreign members of the US National Academy of Sciences) wrote about this in a Physics Today obituary for Cabibbo His scientific influence was overwhelming. Despite the renaissance of Italian experimental physics after World War II, Italian theoretical physics was slow to start. Thanks to his international achievements, Cabibbo became an exemplar whom both younger physicists and those his age wanted to imitate. He showed that it was possible to have an excellent school of theoretical physics in Italy, as demonstrated by the accomplishments of his students and younger collaborators, including Luciano Maiani, Roberto Petronzio, Guido Martinelli, and me. While always remaining active in teaching and research, Cabibbo also held several key administrative positions. These include the presidency of the Italian National Institute of Nuclear Physics (INFN) from 1983 to 1992, the presidency of the Italian energy agency ENEA from 1993 to 1998, and the chairmanship of the scientific council at the Abdus Salam International Centre for Theoretical Physics (ICTP). From 1993 on, he was also president of the Pontifical Academy of Sciences, a grouping of the world’s leading scientists assembled as an independent body for the purpose of research. From this post, Cabibbo was an outspoken defender of the theory of evolution. Though Cabibbo is most famous for his work in the field of weak interactions, an area in which he remained active in a very significant way until his death, he also was a pioneer in the study of how quarks interact with each other by the exchange of so-called colored gluons. This theory, quantum chromodynamics or QCD, forms the basis of the modern theory of strong interactions. Because of this very strength, the problem of how quarks interact cannot be studied perturbatively, as is done for the weak interactions. In order to examine its features, Cabibbo together with Giorgio Parisi proposed and built a dedicated supercomputer with which they explored the phase transition that quarks and gluons undergo at high densities. The array processor experiment, or APE, was a pioneer in such studies. Its predictions are now being tested at the Large Hadron Collider. Cabibbo’s many honors include in 1982 election as a foreign member to the US National Academy of Sciences, the 1989 American Physical Society’s Sakurai Prize, in 1991 the first European Physical Society’s Prize in high-energy physics and in 2010, the Dirac Medal of the International Center for Theoretical Physics. 2. 2011 Benjamin Franklin Medal in Physics Citation: for explaining how the weak interaction decays of different types of elementary particles are related to one another.
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G. Segre / Journal of the Franklin Institute 351 (2014) 117–120
3. Benjamin Franklin Medal in Physics medal legacy Previous scientists who, like Nicola Cabibbo, have worked to understand the nature of the atomic and sub-atomic world include: 1927
1935 1947
1952
1967
1976
1976
1979 1992 1995 2005
Max Planck (Franklin Medal) For his law of radiation and the idea of the fundamental indivisible quantity of radiant energy called the quantum Albert Einstein (Franklin Medal) For his work on relativity and the photo-electric effect Enrico Fermi (Franklin Medal) For research in practical use of energy stored in the nuclei of certain heavy atoms Wolfgang Pauli (Franklin Medal) For work in the understanding of atomic physics and formulation of exclusion principle Murray Gell-Mann (Franklin Medal) For the introduction of concept of strangeness and the eight-fold way to elementary particle physics Val L. Fitch (Wetherill Medal) For work in elucidating the symmetries of the physical laws and for fundamental discoveries implying the failure of time reversal invariance for elementary particles Leon M. Lederman (Cresson Medal) For leadership in forefront of experimentation in study of high energy interactions, nuclear forces and particle physics Steven Weinberg (Cresson Medal) For a unified theory of weak and electromagnetic interactions Frederick Reines (Franklin Medal) For the experimental discovery of the neutrino Gerard ‘t Hooft (Franklin Medal) For laying the foundation for a unified field theory Yoichiro Nambu (Benjamin Franklin Medal in Physics) For his path-breaking contributions leading to our modern understanding of sub-atomic particles—the Standard Model
Journal of the Franklin Institute 351 (2014) 117–120 www.elsevier.com/locate/jfranklin
The 2011 Benjamin Franklin Medal in Physics presented to Nicola Cabibbo Gino Segre n Department of Physics and Astronomy, University of Pennsylvania, PA, USA Received 6 June 2012; received in revised form 6 June 2012; accepted 6 June 2012 Available online 11 January 2013
Abstract The Franklin Institute of Philadelphia awards the 2011 Benjamin Franklin Medal in Physics to Nicola Cabibbo for his pioneering work in the field of elementary particle physics, with special emphasis on his role in furthering our understanding of the underlying symmetries that relate one elementary particle interaction to another. Cabibbo, who tragically died in Rome on the 16th of August, 2010, was one of the most brilliant theoretical physicists of the post-World War II period, universally known in the world of physics for his theory describing the decay by weak interactions of particles containing the quantum property known as strangeness. In more than 200 published papers, Cabibbo also made fundamental contributions to other areas of elementary particle physics, including descriptions of electron–positron scattering, the development and application of supercomputers for calculations of quark interactions, and the theory of neutrino oscillations. & 2013 The Franklin Institute. Published by Elsevier Ltd. All rights reserved.
1. Introduction The field of elementary particle physics came into existence as a separate subfield of physics during the 1950s with the building of the accelerators that propelled particles toward either a fixed target or toward each other, the latter being the case in colliding beam accelerators. During this era’s initial phase, a plethora of particles was discovered, many carrying the new quantum number known as strangeness. More massive than the already n
Tel.: þ1 215 247 9453. E-mail address: [email protected]
0016-0032/$32.00 & 2013 The Franklin Institute. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jfranklin.2012.06.011
118
G. Segre / Journal of the Franklin Institute 351 (2014) 117–120
known neutron, proton, and pi meson, the new particles were seen to decay rapidly into lower mass states composed of the former mentioned particles. There were in fact so many new particles being discovered that serious attempts were made to find underlying symmetries that related them to one another in a meaningful way. The most successful effort along these lines was made by Murray Gell-Mann, who proposed in 1961 the existence of the SU(3) symmetry, alternatively known as either the unitary symmetry or as ‘‘The Eightfold Way.’’ His achievement was recognized with The Franklin Institute’s Franklin Medal in 1967 and with the Nobel Prize in 1969. But many problems remained in 1961 in applying the notion of this symmetry to both strongly interacting particles, known as hadrons, and to leptons, particles that have no strong interactions. This is where Cabibbo entered the scene. His paper ‘‘Unitary Symmetry and Leptonic Decays’’, appearing in Physical Review Letters in the summer of 1963, was a watershed in the theory of elementary particles and a key component in establishing what has come to be known as the ‘‘Standard Model of Elementary Particles’’. It remains the most cited paper of the more than 350,000 published by the American Physical Society since 1893. Cabibbo’s singular achievement is most easily understood in the language of quarks, a concept not yet developed at the time of his proposal. This holds that all strongly interacting particles, hadrons, are composed of elementary constituents, quarks, that appear in six varieties: up, down, strange, charm, top, and bottom. They are matched by six leptons—three kinds of neutrinos and electron, muon, and tau. Cabibbo’s work originated from a need to explain two observed phenomena: (1) the transitions between up and down quarks, as well as those between electrons, muons and their companion neutrinos, had similar likelihood of occurring (similar amplitudes) and (2) the transitions with change in strangeness had amplitudes equal approximately to onefourth of those with no change in strangeness. Cabibbo solved the first issue by extending the notion of weak universality, which involves a similarity in the weak interaction coupling strength between different generations of particles. He solved the second issue by invoking a mixing angle yC (now called the Cabibbo angle) in the coupling between the down and strange quarks. Measurements confirmed his hypothesis; the present experimentally determined value of yC is approximately 131. Though Cabibbo’s theory, based on symmetry arguments, was not formulated in terms of quarks, its extension to them was both simple and natural. In 1970, Sheldon Glashow, John Iliopoulos, and Luciano Maiani showed that the rarity of double-strangeness-changing events could be explained in the framework of Cabibbo’s theory by the existence of a fourth (charmed) quark. In 1973, Makoto Kobayashi and Toshihide Maskawa displayed how the extension to a six-quark model could explain the presence of CP (the combination of charge symmetry and parity) violations in weak interactions. This led to a formulation of the 3 3 complex matrix describing the weak interaction decays of all six quarks, a quantity that has been intensively studied both theoretically and experimentally ever since. Known as the CKM or Cabibbo– Kobayashi–Maskawa matrix, it remains a cornerstone of modern elementary particle physics. It had generally been assumed that the three CKM authors would receive the Physics Nobel Prize, so there was a good deal of surprise when it was announced that the 2008 Prize would be awarded half to Yoichiro Nambu and the other half to be shared by Kobayashi and Maskawa. This was particularly true since many felt that the key insight that led to the CKM matrix’s formulation was Cabibbo’s, but in his usual gentlemanly fashion, he refused to be critical of the judgment that had been made.
G. Segre / Journal of the Franklin Institute 351 (2014) 117–120
119
Born in Rome in 1935, Cabibbo graduated from the University of Rome I (‘‘La Sapienza’’) in 1958 after completing a thesis on weak interactions under Bruno Touschek. He then went to the Frascati National Laboratories, where he worked with Raoul Gatto on a comprehensive study of electron–positron interactions; that work had a decisive role in shaping research with colliding-beam accelerators. Cabibbo became a full professor in 1965 at the University of L’Aquila, he moved to Rome’s La Sapienza, where he taught from 1966 to 1981; to the University of Rome II (‘‘Tor Vergata’’), where he was a professor from 1981 to 1993; and then back to La Sapienza, where he taught until 2010. He spent considerable time abroad, both in the United States and Europe, during his formative years, but always returned to Rome. Though his influence on physics was enormous, it was particularly strongly felt in Italy. The very well known theoretical physicist Giorgio Parisi (among many honors, one of the few foreign members of the US National Academy of Sciences) wrote about this in a Physics Today obituary for Cabibbo His scientific influence was overwhelming. Despite the renaissance of Italian experimental physics after World War II, Italian theoretical physics was slow to start. Thanks to his international achievements, Cabibbo became an exemplar whom both younger physicists and those his age wanted to imitate. He showed that it was possible to have an excellent school of theoretical physics in Italy, as demonstrated by the accomplishments of his students and younger collaborators, including Luciano Maiani, Roberto Petronzio, Guido Martinelli, and me. While always remaining active in teaching and research, Cabibbo also held several key administrative positions. These include the presidency of the Italian National Institute of Nuclear Physics (INFN) from 1983 to 1992, the presidency of the Italian energy agency ENEA from 1993 to 1998, and the chairmanship of the scientific council at the Abdus Salam International Centre for Theoretical Physics (ICTP). From 1993 on, he was also president of the Pontifical Academy of Sciences, a grouping of the world’s leading scientists assembled as an independent body for the purpose of research. From this post, Cabibbo was an outspoken defender of the theory of evolution. Though Cabibbo is most famous for his work in the field of weak interactions, an area in which he remained active in a very significant way until his death, he also was a pioneer in the study of how quarks interact with each other by the exchange of so-called colored gluons. This theory, quantum chromodynamics or QCD, forms the basis of the modern theory of strong interactions. Because of this very strength, the problem of how quarks interact cannot be studied perturbatively, as is done for the weak interactions. In order to examine its features, Cabibbo together with Giorgio Parisi proposed and built a dedicated supercomputer with which they explored the phase transition that quarks and gluons undergo at high densities. The array processor experiment, or APE, was a pioneer in such studies. Its predictions are now being tested at the Large Hadron Collider. Cabibbo’s many honors include in 1982 election as a foreign member to the US National Academy of Sciences, the 1989 American Physical Society’s Sakurai Prize, in 1991 the first European Physical Society’s Prize in high-energy physics and in 2010, the Dirac Medal of the International Center for Theoretical Physics. 2. 2011 Benjamin Franklin Medal in Physics Citation: for explaining how the weak interaction decays of different types of elementary particles are related to one another.
120
G. Segre / Journal of the Franklin Institute 351 (2014) 117–120
3. Benjamin Franklin Medal in Physics medal legacy Previous scientists who, like Nicola Cabibbo, have worked to understand the nature of the atomic and sub-atomic world include: 1927
1935 1947
1952
1967
1976
1976
1979 1992 1995 2005
Max Planck (Franklin Medal) For his law of radiation and the idea of the fundamental indivisible quantity of radiant energy called the quantum Albert Einstein (Franklin Medal) For his work on relativity and the photo-electric effect Enrico Fermi (Franklin Medal) For research in practical use of energy stored in the nuclei of certain heavy atoms Wolfgang Pauli (Franklin Medal) For work in the understanding of atomic physics and formulation of exclusion principle Murray Gell-Mann (Franklin Medal) For the introduction of concept of strangeness and the eight-fold way to elementary particle physics Val L. Fitch (Wetherill Medal) For work in elucidating the symmetries of the physical laws and for fundamental discoveries implying the failure of time reversal invariance for elementary particles Leon M. Lederman (Cresson Medal) For leadership in forefront of experimentation in study of high energy interactions, nuclear forces and particle physics Steven Weinberg (Cresson Medal) For a unified theory of weak and electromagnetic interactions Frederick Reines (Franklin Medal) For the experimental discovery of the neutrino Gerard ‘t Hooft (Franklin Medal) For laying the foundation for a unified field theory Yoichiro Nambu (Benjamin Franklin Medal in Physics) For his path-breaking contributions leading to our modern understanding of sub-atomic particles—the Standard Model