The theta meson ({Subatomic particle|Theta meson}) is a hypothetical form of quarkonium (i.e. a flavourless meson) formed by a top quark and top antiquark. It is the equivalent of the phi (strange quark, strange antiquark), psi (charm quark, charm antiquark) and upsilon (bottom quark, bottom antiquark) mesons. Due to the top quark`s shortlifetime....