Candidates for Chiral Particles

The covariant level-classification scheme of hadrons with Ũ(12)SF ⊗ O(3, 1)L symmetry has been proposed, 1) which gives a covariant quark representation for composite hadrons with definite Lorentz and chiral transformation properties. This covariant classification scheme unifies two seemingly contradictory viewpoints, nonrelativistic and extremely relativistic ones, of quark-model classification for hadrons. The one is based on the nonrelativistic quark model with SU(6)SF ⊗O(3)L symmetry and the other stems from the fact that the lightest pseudoscalar mesons of the flavor octet (π, K, K, η) can be identified with the Nambu-Goldstone bosons associated with spontaneous breaking of chiral symmetry, which plays an important role in the low-energy hadron physics. In this scheme it is predicted that there exist additional states of hadrons, called chiralons, which do not appear in the conventional scheme based on nonrelativistic quark models. In the case of mesons, there appear mesonic chiralons for light-quark qq and heavy-light-quark Qq and qQ systems,∗) while for heavy-quark QQ systems the covariant level-classification scheme gives the same results on existing states as the conventional nonrelativistic classification scheme, so that there exist no mesonic chiralons. Here we restrict our discussion to light-quark meson systems and in order to find possible candidates for mesonic chiralons we try to assign all the known lightunflavored and strange mesons with masses below about 1.8 GeV to the flavor qq nonets which exist in the covariant level-classification scheme.