http://www.ck12.org Chapter 22. The Nucleus
22.4 Quarks
- Describe the quark content of the proton and neutron.
- Describe the additional quarks in the quark model.
The first suggestion of the existence of quarks was presented in 1964 by Murray Gell-Mann and George Zweig.
They suggested that protons and neutrons were composed of three quarks called up (u), down (d), and strange (s).
A fourth quark was hypothesized just for reasons of symmetry and the name “charm” was suggested for the fourth
quark by Sheldon Glashow and James Bjorken. The first evidence for quarks was produced by an experiment in the
Stanford Linear Accelerator by James Bjorken and Richard Feynman in 1968. In 1974, Burton Richter and Samuel
Ting, separately, announce on the same day that they discovered the same new particle. Ting and his collaborators
at Brookhaven called this particle the “J” particle, whereas Richter and his collaborators at SLAC called this particle
the psi particle. Since the discoveries are given equal weight, the particle is commonly known as the J/psi particle.
The J/psi particle is a charm-anti-charm meson. After eighteen years of searching at many accelerators, experiments
at Fermilab in 1995 discovered the top quark.
Quarks
When the atomic theory was first suggested, the atoms were considered to be indivisible. Sometime later, it
was determined that, in fact, atoms were not indivisible but had component parts, namely protons, neutrons, and