The Neutral Kaon System

Abstract

There are four strange pseudoscalar mesons K⁺, K^-, K⁰ and K̄⁰, which are all eigenstates of the Hamiltonian of the strong interaction. Their quark content,

$$\begin{array}{*{20}{c}} {{{K}^{ + }} = (\bar{s}u)} & , & {{{K}^{0}} = (\bar{s}d)} & , \\ {{{K}^{ - }} = (\bar{u}s)} & , & {{{{\bar{K}}}^{0}} = (s\bar{d})} & , \\ \end{array}$$

(8.1)

shows that K⁺ and K^- form a conjugate particle-antiparticle pair, as does the pair K⁰ and K̄⁰. We are used to thinking that the charge of an antiparticle is opposite to that of a particle, as is the case for the pair K⁺, K^-. The pair K⁰, K̄⁰, however, is neutral. Nevertheless, the K⁰ differs from the K̄⁰ in the sign of other quantum numbers, namely isospin and strangeness:

$$\begin{array}{*{20}{c}} {{{K}^{0}}:T = \frac{1}{2}} & , & {{{T}_{3}} = - \frac{1}{2}} & , & {S = + 1} & , \\ {{{{\bar{K}}}^{0}}:T = \frac{1}{2}} & , & {{{T}_{3}} = + \frac{1}{2}} & , & {S = - 1} & . \\ \end{array}$$

(8.2)

See Vol. 2 of this series W. Greiner and B. Müller: Quantum Mechanics — Symmetries (Springer, Berlin, Heidelberg, New York 1989).