One of the fundamental questions is that “what the matter is composed of?” In 1897, atoms are known as the basic building blocks of matter. In the year 1911, Ernest Rutherford demonstrated that when alpha particles are scattered on a thin gold foil that the atom is composed of mostly empty space with a dense core at its center which is called the nucleus. Thereafter, protons and neutrons were discovered. In 1956, McAllister and Hofstadter published experimental results of elastic scattering of the electrons from a hydrogen target which revealed that the proton has an internal structure. In 1964, Gell-Mann (and independently) Zweig proposed that nucleons are composed of point-like particles which are called quarks. These quarks are postulated to have spin-1/2, fractional electric charge. Combinations of different flavors of quarks yield protons and neutrons which belong to the type of particles called baryons (built up from three quarks) and mesons as (quark and an antiquark). These two groups of particles are categorized as hadrons. The quarks showed further decay properties which suggested that they have a substructure.