Particle physics is a branch of physics which studies the nature of particles that are the constituents of what is usually referred to as matter - particles with mass; and radiation - mass-less particles.
In current understanding, particles are excitations of quantum fields and interact following their dynamics. Although the word particle
can be used in reference to many objects (e.g. a proton, a gas particle, or even household dust), the term particle physics
usually refers to the study of smallest
particles and the fundamental fields that must be defined in order to explain the observed particles.
The current set of fundamental fields and their dynamics are summarized in a theory called the Standard Model, therefore particle physics is largely the study of the Standard Model's particle content and its possible extensions, with the recent finding of Higgs boson.
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