James Bjorken

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{{Infobox scientist |name = James Bjorken |image = James Bjorken.jpg |image_size = |alt = |caption = |birth_date = June 22, 1934 |birth_place = Chicago |death_date = |death_place = |residence = |citizenship = |nationality = American |ethnicity = |fields = Theoretical physics |workplaces = Fermilab, SLAC |alma_mater = MIT (B.S., 1956)
Stanford University (Ph.D., 1959) |doctoral_advisor = |academic_advisors = |doctoral_students = Davison Soper |notable_students = |known_for = Bjorken scaling, Co-predicting the charm quark |author_abbrev_bot = |author_abbrev_zoo = |influences = |influenced = |awards = Putnam Fellow (1954)
Heineman Prize (1972)
E. O. Lawrence Award (1977)
Pomeranchuk Prize (2000)
ICTP Dirac Medal (2004)
Wolf Prize in Physics (2015)

James Daniel "BJ" Bjorken (born 1934) is an American theoretical physicist. He was a Putnam Fellow in 1954, received a BS in physics from MIT in 1956, and obtained his PhD from Stanford University in 1959. He was a visiting scholar at the Institute for Advanced Study in the fall of 1962.[1] Bjorken is Emeritus Professor at the Stanford Linear Accelerator Center, and was a member of the Theory Department of the Fermi National Accelerator Laboratory (1979–1989). He was awarded the Dirac Medal of the ICTP in 2004 and in 2015 the Wolf Prize in Physics.

Bjorken discovered what is known as light-cone scaling, (or "Bjorken scaling") a phenomenon in the deep inelastic scattering of light on strongly interacting particles, known as hadrons (such as protons and neutrons). This was critical to the recognition of quarks as actual elementary particles (rather than just convenient theoretical constructs), and led to the theory of strong interactions known as quantum chromodynamics. In Bjorken's picture, the quarks become point-like, observable objects at very short distances (high energies).

Richard Feynman subsequently reformulated this concept into the parton model, used to understand the quark composition of hadrons at high energies.[2] The predictions of Bjorken scaling were confirmed in the early late 1960s electroproduction experiments at SLAC, 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, with Sidney Drell, a classic companion volume textbook on relativistic quantum mechanics and quantum fields.

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