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

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 $D^{\ast }{\bar{D}}_1$ 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 $J=1,2$ $D_s^{\ast }{\bar{D}}_{s1}$ and $J=3$ $D_s^{\ast }{\bar{D}}_{s2}^{\ast }$ bound states with a mass in the vicinity of $4630\mathrm{MeV}$, 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 $D^{\ast }{\bar{D}}_1$-$D^{\ast }{\bar{D}}_2^{\ast }$ and $D_s^{\ast }{\bar{D}}_{s1}$-$D_s^{\ast }{\bar{D}}_{s2}^{\ast }$ thresholds and include the related coupled channel dynamics, we predict a $J=2$ positive C-parity state with a mass around $4650\mathrm{MeV}$. 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 $J/\psi \varphi$ invariant mass distribution.

Comments: 21 pages, 7 tables