Heavy quark spin symmetry breaking in near-threshold JPC=1-- quarkoniumlike resonances

A mixing of near-threshold quarkoniumlike resonances with heavy meson-antimeson pairs results in an enhancement of heavy quark spin symmetry breaking, since the meson pairs are not eigenstates of the heavy quark spin. The decomposition of P-wave states of meson pairs in terms of the heavy quark pair spin states is considered in the channel with J(PC) = 1(--), which is directly produced in e(+)e(-) annihilation. Specific processes are suggested for experimental study of the effects of the mixing with heavy meson pairs and of the internal spin structure of bottomonium and charmonium resonances.