James Daniel "BJ" Bjorken (born 1934) is an American

theoretical physicist Theoretical physics is a branch of physics that employs mathematical models and abstractions of physical objects and systems to rationalize, explain and predict natural phenomena. This is in contrast to experimental physics, which uses experime ...

. He was a Putnam Fellow in 1954, received a BS in physics from

MIT The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the m ...

in 1956, and obtained his PhD from

Stanford University Stanford University, officially Leland Stanford Junior University, is a private research university in Stanford, California. The campus occupies , among the largest in the United States, and enrolls over 17,000 students. Stanford is conside ...

in 1959. He was a visiting scholar at the

Institute for Advanced Study The Institute for Advanced Study (IAS), located in Princeton, New Jersey, in the United States, is an independent center for theoretical research and intellectual inquiry. It has served as the academic home of internationally preeminent schola ...

in the fall of 1962. Bjorken is Emeritus Professor in the

SLAC Theory Group The SLAC Theory Group is the hub of theoretical particle physics research at the SLAC National Accelerator Laboratory at Stanford University. It is a subdivision of the Elementary Particle Physics (EPP) Division at SLAC. Research The group has ...

at the

Stanford Linear Accelerator Center SLAC National Accelerator Laboratory, originally named the Stanford Linear Accelerator Center, is a United States Department of Energy National Laboratory operated by Stanford University under the programmatic direction of the U.S. Departme ...

, and was a member of the Theory Department of the

Fermi National Accelerator Laboratory Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a United States Department of Energy national laboratory specializing in high-energy particle physics. Since 2007, Fermilab has been operat ...

(1979–1989). He was awarded the

Dirac Medal of the ICTP The Dirac Medal is the name of four awards in the field of theoretical physics, computational chemistry, and mathematics, awarded by different organizations, named in honour of Professor Paul Dirac, one of the great theoretical physicists of the ...

in 2004; and, in 2015, the

Wolf Prize in Physics The Wolf Prize in Physics is awarded once a year by the Wolf Foundation in Israel. It is one of the six Wolf Prizes established by the Foundation and awarded since 1978; the others are in Agriculture, Chemistry, Mathematics, Medicine and Arts ...

and the EPS

High Energy and Particle Physics Prize The High Energy and Particle Physics Prize, established in 1989, is awarded every two years by the European Physical Society (EPS) for an outstanding contribution to high energy and particle physics. :) Enjoy Recipients Source: * 1989 Georges C ...

Early life and education

James Bjorken's father, J. Daniel Bjorken, was an immigrant from Sweden near Lake 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 is where he met his future wife, Edith. James Bjorken grew up in Chicago and enjoyed mathematics, chemistry, the French horn, and watching the

Chicago Cubs The Chicago Cubs are an American professional baseball team based in Chicago. The Cubs compete in Major League Baseball (MLB) as part of the National League (NL) Central division. The club plays its home games at Wrigley Field, which is locate ...

play at

Wrigley Field Wrigley Field is a Major League Baseball (MLB) stadium on the North Side of Chicago, Illinois. It is the home of the Chicago Cubs, one of the city's two MLB franchises. It first opened in 1914 as Weeghman Park for Charles Weeghman's Chicago ...

. After graduating from Maine East High School in 1952, he decided to attend

Massachusetts Institute of Technology The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of th ...

(MIT) over the

University of Chicago The University of Chicago (UChicago, Chicago, U of C, or UChi) is a private research university in Chicago, Illinois. Its main campus is located in Chicago's Hyde Park neighborhood. The University of Chicago is consistently ranked among the b ...

. 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. At MIT, he quickly decided to major in physics; one of the main reasons was his enjoyment of the lectures that Hans Mueller gave. Another of his influences at MIT was

Sidney Drell Sidney David Drell (September 13, 1926 – December 21, 2016) was an American theoretical physicist and arms control expert. At the time of his death, he was professor emeritus at the Stanford Linear Accelerator Center (SLAC) and senior fe ...

, who became his mentor. After graduating in 1956, he attended

, graduating with his PhD in 1959 and staying on as a postdoctoral researcher for several years.

Work

Bjorken discovered in 1968 what is known as '' light-cone scaling'' (or ''Bjorken scaling''), a phenomenon in the

deep inelastic scattering Deep inelastic scattering is the name given to a process used to probe the insides of hadrons (particularly the baryons, such as protons and neutrons), using electrons, muons and neutrinos. It provided the first convincing evidence of the realit ...

of light on strongly interacting particles, known as ''

hadron In particle physics, a hadron (; grc, ἁδρός, hadrós; "stout, thick") is a composite subatomic particle made of two or more quarks held together by the strong interaction. They are analogous to molecules that are held together by the ...

s'' (such as

proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...

s and

neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the atomic nucleus, nuclei of atoms. Since protons and ...

s): 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 of

quark A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. All commonly ...

s as actual

elementary particle In particle physics, an elementary particle or fundamental particle is a subatomic particle that is not composed of other particles. Particles currently thought to be elementary include electrons, the fundamental fermions ( quarks, leptons, ...

s (rather than just convenient theoretical constructs), and led to the theory of

strong interaction The strong interaction or strong force is a fundamental interaction that confines quarks into proton, neutron, and other hadron particles. The strong interaction also binds neutrons and protons to create atomic nuclei, where it is called th ...

s known as

quantum chromodynamics In theoretical physics, quantum chromodynamics (QCD) is the theory of the strong interaction between quarks mediated by gluons. Quarks are fundamental particles that make up composite hadrons such as the proton, neutron and pion. QCD is a type ...

, where it was understood in terms of the

asymptotic freedom In quantum field theory, asymptotic freedom is a property of some gauge theories that causes interactions between particles to become asymptotically weaker as the energy scale increases and the corresponding length scale decreases. Asymptotic fre ...

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 the ''Bjorken sum rule'',J. D. Bjorken (1966) “Applications of the chiral U(6)×U(6) algebra of current densities”
Phys. Rev. 148, 1467J. D. Bjorken (1970) “Inelastic scattering of polarized leptons from polarized nucleons”
Phys. Rev. D 1, 1376 the prototypical QCD spin sum rule. It states that in the ''Bjorken scaling'' domain, the integral of the spin

structure function The structure function (also known as the proton structure function), like the fragmentation function, is a probability density function in physics. It is somewhat analogous to the structure factor in solid-state physics, and the form factor (quant ...

of the

minus that of the

is proportional to the axial charge of the

nucleon In physics and chemistry, a nucleon is either a proton or a neutron, considered in its role as a component of an atomic nucleus. The number of nucleons in a nucleus defines the atom's mass number (nucleon number). Until the 1960s, nucleons were ...

. Specially: , where is the Bjorken scaling variable, is the first spin

of the proton (neutron), and is the nucleon axial charge that characterizes the neutron β-decay. The sum rule was experimentally verified within better than a 10% precision.A. Deur, S. J. Brodsky, G. F. de Teramond (2019) “The Spin Structure of the Nucleon”
Rept. Prog. Phys. 82 076201 Bjorken was also among the first to point out to the phenomena of jet quenching in heavy ion collisions in 1982.

Richard Feynman Richard Phillips Feynman (; May 11, 1918 – February 15, 1988) was an American theoretical physicist, known for his work in the path integral formulation of quantum mechanics, the theory of quantum electrodynamics, the physics of the superfl ...

subsequently reformulated this concept into the parton model, used to understand the quark composition of hadrons at high energies.The Parton Model by P. Hansson, KTH, November 18, 2004
PDF file The predictions of Bjorken scaling were confirmed in the early late 1960s electroproduction experiments at

SLAC SLAC National Accelerator Laboratory, originally named the Stanford Linear Accelerator Center, is a United States Department of Energy National Laboratory operated by Stanford University under the programmatic direction of the U.S. Departme ...

, in which quarks were seen for the first time. The general idea, with small logarithmic modifications, is explained in quantum chromodynamics by "

". Bjorken co-authored, with

, a classic companion volume textbook on

relativistic quantum mechanics In physics, relativistic quantum mechanics (RQM) is any Poincaré covariant formulation of quantum mechanics (QM). This theory is applicable to massive particles propagating at all velocities up to those comparable to the speed of light ...

and

quantum field In theoretical physics, quantum field theory (QFT) is a theoretical framework that combines classical field theory, special relativity, and quantum mechanics. QFT is used in particle physics to construct physical models of subatomic particles ...

Publications

Books

* *

Selected papers

*J. D. Bjorken (1968). "Current Algebra at Small Distances", in ''Proceedings of the International School of Physics Enrico Fermi Course XLI'', J. Steinberger, ed., Academic Press, New York, pp. 55–81.
Online, SLAC-PUB-338
* *

Full list of papers

INSPIRE-HEP -- Bjorken

Notes

References

Oral history interview transcript with James Bjorken on 1 April 2020, American Institute of Physics, Niels Bohr Library and ArchivesSLAC Bio APS bio Wu-Ki Tung, "Bjorken Scaling"
in ''Scholarpedia'' (2009).
Wolf prize

External links

{{DEFAULTSORT:Bjorken, James D. Members of the United States National Academy of Sciences 1934 births Living people 21st-century American physicists Putnam Fellows Institute for Advanced Study visiting scholars Theoretical physicists Foreign Members of the Russian Academy of Sciences MIT Department of Physics alumni Stanford University alumni Fellows of the American Physical Society Wolf Prize in Physics laureates American people of Swedish descent Members of the Royal Swedish Academy of Sciences