Theta meson

The theta meson (Theta meson) is a hypothetical form of quarkonium (i.e. a flavourless meson) formed by a top quark and top antiquark. As a P-odd and C-odd state, it is analogous to the phi meson, J/psi meson  and upsilon meson  mesons. Due to the top quark's short lifetime, the theta meson is expected to not be observed in nature.