The particles category implements the facilities necessary to
describe the physical properties of particles for the simulation
of particle-matter interactions. All particles are based on the
G4ParticleDefinition class, which describes basic properties
such as mass, charge, etc., and also allows the particle to
carry a list of processes to which it is sensitive. A first-
level extension of this class defines the interface for
particles that carry cuts information, for example range cut
versus energy cut equivalence. A set of virtual, intermediate
classes for leptons, bosons, mesons, baryons, etc., allows the
implementation of concrete particle classes which define the
actual particle properties and, in particular, implement the
actual range versus energy cuts equivalence. All concrete
particle classes are instantiated as singletons to ensure that
all physics processes refer to the same particle properties. The
object-oriented design of the 'particles' related classes is
shown in the following class diagrams. Th