His research enabled the discovery that protons and neutrons are made of smaller particles, contributing to a fuller picture of the subatomic universe.
James Bjorken, a theoretical physicist who played a key role in establishing the existence of the subatomic particles called quarks, died on Aug. 6 in Redwood City, Calif. He was 90.
His death, in an assisted living facility near his home in Sky Londa, Calif., was caused by metastatic melanoma, his daughter Johanna Bjorken said.
Dr. Bjorken, who was known as B.J., was a professor at Stanford University and the SLAC National Accelerator Laboratory in Menlo Park, Calif., in the late 1960s when he invented what would come to be known as “Bjorken scaling,” which the laboratory described as “his most famous scientific achievement.”
At the time, physicists at SLAC were firing electrons at nucleons — protons and neutrons — to study their nature. The electrons functioned somewhat like magnifying glasses: When fired at high enough energies, they allowed physicists to “see” the nucleon’s inner structure.
Two quantities helped characterize these collisions: the energy at which the strike occurred and the energy of the outgoing electron. Dr. Bjorken proposed that the behavior of the collisions depended not on these two quantities separately, but on a particular combination of them.