James Bjorken | |
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| Born | James Daniel Bjorken (1934-06-22)June 22, 1934 Chicago, Illinois, U.S. |
| Died | August 6, 2024(2024-08-06) (aged 90) Redwood City, California, U.S. |
| Alma mater | Massachusetts Institute of Technology (BS) Stanford University (PhD) |
| Known for | Bjorken scaling Intrabeam scattering Jet quenching Co-predicting thecharm quark |
| Spouse | |
| Children | 2 |
| Awards | Putnam Fellow(1954) Heineman Prize(1972) E. O. Lawrence Award(1977) Pomeranchuk Prize(2000) ICTP Dirac Medal(2004) Wolf Prize in Physics(2015) EPSHigh Energy and Particle Physics Prize(2015) |
| Scientific career | |
| Fields | Theoretical physics |
| Institutions | Fermilab,SLAC |
| Thesis | Experimental tests of Quantum electrodynamics and spectral representations of Green's functions in perturbation theory (1959) |
| Doctoral advisor | Sidney Drell |
| Doctoral students | John Kogut Davison Soper Helen Quinn |
James Daniel "BJ"Bjorken (June 22, 1934 – August 6, 2024) was an Americantheoretical physicist. He was aPutnam Fellow in 1954,[1] received a BS in physics fromMIT in 1956, and obtained his PhD fromStanford University in 1959. Bjorken was a visiting scholar at theInstitute for Advanced Study in the fall of 1962.[2] He was also emeritus professor in theSLAC Theory Group at theStanford Linear Accelerator Center, and was a member of the Theory Department of theFermi National Accelerator Laboratory (1979–1989).
Bjorken was awarded theDirac Medal of the ICTP in 2004; and, in 2015, theWolf Prize in Physics and theEPSHigh Energy and Particle Physics Prize.[3]
James Bjorken's father, J. Daniel Bjorken, was an immigrant from Sweden nearLake Siljan. He changed his surname from "Björkén" to Bjorken upon arriving in the US; he moved to Chicago to work as an electrical engineer, which was where he met his future wife, Edith. James Bjorken grew up in Chicago and enjoyed mathematics, chemistry, the French horn, and watching theChicago Cubs play atWrigley Field. After graduating fromMaine East High School in 1952, he decided to attendMassachusetts Institute of Technology (MIT) over theUniversity of Chicago. Despite being offered more financial aid to attend the University of Chicago, his parents advised him that he should move further away to find his independence.[4]
At MIT, he quickly decided to major in physics; one of the main reasons was his enjoyment of the lectures thatHans Mueller gave. Another of his influences at MIT wasSidney Drell, who became his mentor. After graduating in 1956, he attendedStanford University, graduating with his PhD in 1959 and staying on as a postdoctoral researcher for several years.[4]
Bjorken discovered in 1968 what is known aslight-cone scaling (orBjorken scaling), a phenomenon in thedeep inelastic scattering of light onstrongly interacting particles, known ashadrons (such asprotons andneutrons):Experimentally observed hadrons behave as collections of virtually independent point-like constituents when probed at high energies.
Properties of these hadrons scale, that is, they are determined not by the absolute energy of an experiment, but, instead, by dimensionless kinematic quantities, such as a scattering angle or the ratio of the energy to a momentum transfer. Because increasing energy implies potentially improved spatial resolution, scaling implies independence of the absolute resolution scale, and hence effectively point-like substructure.
This observation was critical to the recognition ofquarks as actualelementary particles (rather than just convenient theoretical constructs), and led to the theory ofstrong interactions known asquantum chromodynamics, where it was understood in terms of theasymptotic freedom property. In Bjorken's picture, the quarks become point-like, observable objects at very short distances (high energies), shorter than the size of the hadrons.
Bjorken also discovered theBjorkensum rule,[5][6] the prototypical QCD spin sum rule. It states that in theBjorken scaling domain, the integral of the spinstructure function of theproton minus that of theneutron is proportional to theaxial charge of thenucleon. Specially:, where is the Bjorken scaling variable, is the first spinstructure function of the proton (neutron), and is the nucleon axial charge that characterizes theneutron β-decay. The sum rule was experimentally verified within better than a 10% precision.[7]
Bjorken was also among the first to point out the phenomena ofjet quenching in heavy ion collisions in 1982.
Richard Feynman subsequently reformulated this concept into theparton model, used to understand the quark composition of hadrons at high energies.[8] The predictions of Bjorken scaling were confirmed in the early late 1960s electroproduction experiments atSLAC, in which quarks were seen for the first time. The general idea, with small logarithmic modifications, is explained in quantum chromodynamics by "asymptotic freedom".
Bjorken co-authored, withSidney Drell, a classic companion volume textbook onrelativistic quantum mechanics andquantum fields.
In 1967, Bjorken married Joan Goldthwaite; they had two children and were married until her death in 1983.[9] He lived inSky Londa, California.[9]
Bjorken died frommelanoma at a care facility inRedwood City, California, on August 6, 2024 at the age of 90.[9][10]
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