The past one hundred years has witnessed enormous advances in human understanding of the physical universe in which we have evolved. For the past fifty years or so, the Standard Model of the subatomic world has been systematically developed to provide the quantum mechanical description of electricity and magnetism, the weak interaction, and the strong force. Symmetry principles, expressed mathematically via group theory, serve as the backbone of the Standard Model. At this time, the Standard Model has passed all tests in the laboratory. Notwithstanding this success, most of the matter available to experimental physicists is in the form of atomic nuclei. The most successful description of nuclei is in terms of the observable protons, neutrons, and other hadronic constituents, and not the fundamental quarks and gluons of the Standard Model. Thus, the professional particle or nuclear physicist should be comfortable in applying the hadronic description of nuclei to understanding the structure and properties of nuclei. Experimentally, lepton scattering has proved to be the cleanest and most effective tool for unraveling the complicated structure of hadrons. Its application over different energies and kinematics to the nucleon, fewbody nuclei, and medium- and heavy-mass nuclei has provided the solid body of precise experimental data on which the Standard Model is built.
In addition, the current understanding of the microcosm described in this book provides answers to many basic questions: How does the Sun shine? What is the origin of the elements? How old is the Earth? Further, it underscores many aspects of modern human civilization, e.g., MRI imaging uses the spin of the proton, nuclear isotopes are essential medical tools, nuclear reactions have powered the Voyager spacecraft since 1977 into interstellar space.
The purpose of the book is to allow the graduate student to understand the foundations and structure of the Standard Model, to apply the Standard Model to understanding the physical world with particular emphasis on nuclei, and to establish the frontiers of current research. There are many outstanding questions that the Standard Model cannot answer. In particular, astrophysical observation strongly supports the existence of dark matter, whose direct detection has thus far remained elusive.