Light- and heavy-quark symmetries and the $Y(4230)$, $Y(4360)$, $Y(4500)$, $Y(4620)$ and $X(4630)$ resonances

TL;DR

This paper explores how heavy-quark symmetries relate various exotic resonances as molecular states of charmed mesons, predicting partner states and connecting them to observed particles like the $Y$ and $X$ states.

Contribution

It formulates an effective field theory linking heavy-quark symmetries to molecular states and predicts new partner states, including the $X(4630)$, based on these symmetries.

Findings

Predicted partner states for known resonances.

Identified potential correspondence of $Y(4620)$ with a predicted bound state.

Connected the $X(4630)$ to a predicted hidden-strange, hidden-charm state.

Abstract

The heavy hadron spectrum is constrained by symmetries, of which two of the most important ones are heavy-quark spin and SU(3)-flavor symmetries. Here we argue that in the molecular picture the $Y(4230)$ (or $Y(4260)$), the $Y(4360)$ and the recently discovered $Y(4500)$ and $Y(4620)$ vector-like resonances are linked by these two symmetries. By formulating a contact-range effective field theory for the $D \bar{D}_1$ and $D_s \bar{D}_{s1}$ family of S- and P-wave charmed meson-antimeson systems, we find that if the $Y(4230)$ were to be a pure $D \bar{D}_1$ molecular state, there would be a $D^* \bar{D}_1$ partner with a mass similar to the $Y(4360)$, a $D_s \bar{D}_{s1}$ partner with a mass close to the $Y(4500)$ and three $J=1,2$ $D_s^* \bar{D}_{s1}$ and $J=3$ $D_s^* \bar{D}_{s2}^{*}$ bound states with a mass in the vicinity of $4630\,{\rm MeV}$, of which the first one ($J=1$) might correspond with the $Y(4620)$. The previous predictions can in turn be improved by modifying the assumptions we have used to build the effective field theory. In particular, if we consider the closeness of the $D^* \bar{D}_1$-$D^* \bar{D}_2^*$ and $D_s^* \bar{D}_{s1}$-$D_s^* \bar{D}_{s2}^*$ thresholds and include the related coupled channel dynamics, we predict a $J=2$ positive C-parity state with a mass around $4650\,{\rm MeV}$. This hidden-strange and hidden-charm state might in turn be identified with the $X(4630)$ that has been discovered past year by the LHCb in the $J/\psi \phi$ invariant mass distribution.