"Particle physics (also known as high energy physics) is a branch of physics that studies the nature of the particles that constitute matter and radiation. Although the word particle can refer to various types of very small objects (e.g. protons, gas particles, or even household dust), particle physics usually investigates the irreducibly smallest detectable particles and the fundamental interactions necessary to explain their behaviour.
In current understanding, these elementary particles are excitations of the quantum fields that also govern their interactions. The currently dominant theory explaining these fundamental particles and fields, along with their dynamics, is called the Standard Model. Thus, modern particle physics generally investigates the Standard Model and its various possible extensions, e.g. to the newest "known" particle, the Higgs boson, or even to the oldest known force field, gravity."
(from Wikipedia)
An Introduction to Particle Physics and the Standard Model
Neutrino Physics (file size: about 11 MB)
Gauge Theories in Particle Physics - A Practical Introduction
Heavy Flavour Physics - Theory and Experimental Results in Heavy Quark Physics and CP Violation (file size: about 13 MB)
Supersymmetric Gauge Field Theory and String Theory