Can experiment distinguish tetraquark scalars, molecules and $\qq$ mesons?

Abstract

Scalar mesons are a key expression of the strong coupling regime of QCD. How those with $I_3=0$ couple to two photons supplies important information about which is transiently ${\bar q}q$ or ${\bar {qq}} qq$ or multi-meson molecule or largely glue, provided (i) we know the location of the corresponding poles in the complex energy plane, and (ii) we have reliable predictions from strong coupling QCD of the radiative widths for these compositions. Number (i) is being supplied by careful analyses of high statistics data particularly that coming from $B$, $D$, $J/\psi$ and $\phi$ decays. Number (ii) is still required, before we can answer the question in the title.