Spectroscopy of atomlike mesonsQq¯in a semirelativistic theory

A semirelativistic theory of an atomlike meson, a bound state of a heavy quark Q and a light antiquark q{}, is developed on the basis of the equation introduced by Fermi and Yang in their composite model of a pion. As for the Qq{} potential, a vector ``Coulomb'' plus scalar linear potential is chosen as an example and the transverse interaction of the gluon exchange is also taken into account. The spin-dependent forces are introduced automatically by applying the Foldy transformation to the heavy quark Q. Furthermore, the transverse gluon term generates additional spin-dependent forces. This model reproduces the mass levels of D (D*), Dₛ (Dₛ*), and B (B*) mesons well. D**(2420) is likely one of the 1¹{P}₁$, ${1}³P₁, or 1³{P}₂$ states.