Spectroscopy of tetraquark states

A complete classification of qqq̄q̄ tetraquark states in terms of the spin-flavor, color, and spatial degrees of freedom was constructed. The permutation symmetry properties of both the spin-flavor and orbital parts of the qq and q̄q̄ subsystems are discussed. This complete classification is general and model independent and it is useful both for model builders and experimentalists. The total wave functions are also explicitly constructed in the hypothesis of ideal mixing; this basis for tetraquark states will enable the eigenvalue problem to be solved for a definite dynamical model. An evaluation of the tetraquark spectrum was obtained from the Iachello mass formula for normal mesons, here generalized to tetraquark systems. This mass formula is a generalization of the Gell-Mann Okubo mass formula, whose coefficients have been upgraded by a study of the latest PDG data. The ground-state tetraquark nonet was identified with f₀(600),κ(800),f₀(980),a₀(980). The diquark-antidiquark limit was also studied.