Effects of heavy meson loops on higher charmonia radiative transitions

Radiative transitions between charmonium states offer an insight into the internal structure of heavy quark bound states within QCD. In this work, we performed a systematically investigation of the radiative transitions of $$\psi (nS) \rightarrow \gamma \chi _{cJ}(mP)$$ψ(nS)→γχcJ(mP) and $$\psi (nD) \rightarrow \gamma \chi _{cJ}(mP)$$ψ(nD)→γχcJ(mP) via intermediate charmed meson loop with a non-relativistic effective field theory. We only focus on the line-shape behavior of the distributions via different intermediate meson loops. Our results show that the coupled-channel effects of these decays are relatively weak, while the coupled channel effects has obvious enhancement when the inial (final) states are closed to the thresholds of charmed-mesons pair.

How to distinguish a molecule from an 'elementary' particle?

We discuss how to use Morgan's pole counting rule to distinguish a molecular state from an 'elementary' particle. As two examples we focus on X(3872) and f0(980) particles. A molecule may be generated from a meson loop bubble chain, and an 'elementary' particle is related to an explicit interaction field in the effective lagrangian and propagates with a Breit–Wigner propagator. For X(3872) it is found that the data favor the 'elementary' particle explanation. For f0(980) the study becomes much more difficult, since highly nonperturbative dynamics is involved. A unitarization model analysis suggests that f0(980)'s property is quite exotic. Unlike other light scalars, it does not behave like a [Formula: see text] state, and could be interpreted as a molecule.