文档介绍：GAUGE THEORIES IN PARTICLE PHYSICS
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QUARKS AND LEPTONS
The Standard Model
The traditional goal of particle physics has been to identify what appear to be
structureless units of matter and to understand the nature of the forces acting
between them. Stated thus, the enterprise has a two-fold aspect: matter on the
one hand, forces on the other. The expectation is that the smallest units of
matter should interact in the simplest way; or that there is a deep connection
between the basic units of matter and the basic forces. The joint matter/force
nature of the enquiry is perfectly illustrated by Thomson’s discovery of the
electron and Maxwell’s theory of the ic field, which together mark
the birth of modern particle physics. The electron was recognized both as
the ‘particle of electricity’—or as we might now say, as an elementary source
of the ic field, with its motion constituting an ic
current—and also as an important constituent of matter. In retrospect, the story
of particle physics over the subsequent one hundred years or so has consisted
in the discovery and study of two new (non-ic) forces—the weak
and the strong forces—and in the search for ‘electron-figures’ to serve both
as constituents of the new layers of matter which were uncovered (first nuclei,
and then hadrons) and also as sources of the new force fields. This effort
has recently culminated in decisive progress: the identification of a collection
of matter units which are indeed analogous to the electron; and the highly
convincing experimental verification of theories of the associated strong and weak
force fields, which incorporate and generalize in a beautiful way the original
electron/ic field relationship. These theories are collectively (and
rather modestly, if uninformatively) called ‘the Standard Model’, to which this
book is intended as an elementary introduction.
In brief, the picture is as follows. There are two types of matter units:
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leptons and quarks. Both hav