Introduction

Abstract

Particles which interact through the strong interaction are called hadrons (from the Greek word for “strong”). They are divided into two classes, baryons (for “heavy”) with half-integer spins and mesons (for “medium” heavy) with integer spins. Baryons include their antimatter counterparts, the antibaryons. The total number of baryons minus that of antibaryons remains constant in any physical process, while mesons can be created or destroyed (provided that energy permits and electric charge is conserved).