Subatomic Particles

The second main idea of the standard quark model is that combinations of one quark and one antiquark form mesons. Pions (π) and kaons (K) are examples of mesons. Thus now we see Yukawa's nuclear force mediator particle, the pion, is really a matter particle made of a quark and an antiquark. There are several kinds of pions. For example, the positively charged pion, π⁺, is made of an up quark and a down antiquark. Similarly there are several kinds of kaons. One kind of kaon, K⁺, is made of an up quark and a strange antiquark. The colorless rule requires that mesons must be made of quarks with opposite color, red and anti-red for example. All mesons are bosons and so have spins of zero h-bar or one h-bar.