TABLE OF CONTENTS In Chapter 9, we discussed the properties of only a few low-mass hadrons discovered prior to the mid 1970s. As the energies of accelerators increased, additional excited states of those particles, but with larger masses and higher spins, as well as particles with new flavors (see Table 9.5) were found. In fact, even by the mid 1960s, there was a whole host of particles to contend with, and it was questioned whether they could all be regarded as fundamental constituents of matter. As we argued previously, even the lightest baryons, namely the proton and the neutron, show indirect evidence of substructure. For example, the large anomalous magnetic moments observed for these particles, especially dramatic for the neutron, imply a complex internal distribution of currents. From the pattern of the observed spectrum of hadrons, Murray Gell-Mann and George Zweig suggested independently in 1964 that all such particles could be understood as composed of quark constituents. As shown in Table 9.5, these constituents had rather unusual properties, and were initially regarded as calculational tools rather than as true physical objects.
A series of measurements performed in the late 1960s at the Stanford Linear Accelerator Center (SLAC) on electron scattering from hydrogen and deuterium revealed that the data could be most easily understood if protons and neutrons were composed of point-like objects that had charges of ?1/3 e and +2/3 e. These experiments, led by Jerome Friedman, Henry Kendall and Richard Taylor, corresponded to a modern parallel...
