Mesons

Abstract

In this chapter we consider all of the mesons that are mixed states of all three light flavours up, down and strange. We discuss the quark structure of the multiplets of pseudoscalar and vector mesons and trace back the mass difference between them to a spin-spin interaction. Of special interest are neutral quark–antiquark states containing a light quark and a heavier s-, c- or b-quark, like the $$\vert \mbox{ $\mathrm{K}^{\mathrm{0}}$}\rangle$$or the $$\mathrm{\vert B}^{\mathrm{0}}\rangle$$and their antiparticles. These mesons have very peculiar properties: particle and antiparticle can oscillate into each other and their weak decays violate conservation of CP symmetry. We will discuss these exciting aspects in some detail.