The quark mixing matrix (Kobayashi-Maskawa matrix) is expanded in powers of a small parameter $\lambda$ equal to $sin{\theta }_c=0.22\mathrm{}$. The term of order ${\lambda }^2$ is determined from the recently measured $B$ lifetime. Two remaining parameters, including the $\mathrm{CP}$-nonconservation effects, enter only the term of order ${\lambda }^3$ and are poorly constrained. A significant reduction in the limit on $\frac{{\epsilon }^{\prime }}{\epsilon }$ possible in an ongoing experiment would tightly constrain the $\mathrm{CP}$-nonconservation parameter and could rule out the hypothesis that the only source of $\mathrm{CP}$ nonconservation is the Kobayashi-Maskawa mechanism.

• Received 22 August 1983

DOI:https://doi.org/10.1103/PhysRevLett.51.1945