Narrow Results

Contrary to almost standard opinion that the $X(3872$) resonance is the $D^{\ast 0}{\bar{D}}^0+\mathrm{\text{c.c.}}$ molecule or the $qc\bar{q}\bar{c}$ four-quark state, we discuss the scenario where the $X(3872)$ resonance is the $c\bar{c}={\chi }_{c1}(2P)$ charmonium which “sits on” the $D^{\ast 0}{\bar{D}}^0$ threshold.

We explain the shift of the mass of the $X(3872)$ resonance with respect to the prediction of a potential model for the mass of the ${\chi }_{c1}(2P)$ charmonium by the contribution of the virtual $D^{\ast }\bar{D}+\mathrm{\text{c.c.}}$ intermediate states into the self energy of the $X(3872)$ resonance. This allows us to estimate the coupling constant of the $X(7872)$ resonance with the $D^{\ast 0}{\bar{D}}^0$ channel, the branching ratio of the $X(3872)\to D^{\ast 0}{\bar{D}}^0+\mathrm{\text{c.c.}}$ decay, and the branching ratio of the $X(3872)$ decay into all non-$D^{\ast 0}{\bar{D}}^0+\mathrm{\text{c.c.}}$ states. We predict a significant number of unknown decays of $X(3872)$ via two gluon: $X(3872)\to \text{gluon gluon}\to \text{hadrons}$.

We suggest a physically clear program of experimental researches for verification of our assumption.

Hadron spectroscopy is revealed by observing heavy resonances. Among various explanations of the internal structure of these hadronic states, hadronic molecules play a unique role. For hadronic molecules, which are associated with meson–meson or meson–baryon interactions, the $\mathrm{\Lambda }$ cutoff is a significant factor in determining the composite states’ binding energies and overall properties. The cutoff becomes important when it comes to the location of hadronic molecules’ masses because it influences the predictions. From this perspective, in the light of cutoff dependency, heavy quark spin partners of near-threshold the ${\chi }_{c0}(3915)$, ${\chi }_{c1}(3872)$, $P_c(4440)$, and $P_c(4457)$ resonances, which are considered as hadronic molecules, are examined.

We perform a systematic study of the bound state problem of and systems by using effective interaction in our chiral quark model. Our results show that both the interactions of and states are attractive, which consequently result in and bound states.

The newly observed exotic mesons above threshold were widely discussed in the molecular picture. To understand deeper their structures, we here discuss the spin () of a heavy quark-antiquark pair in an S-wave meson-antimeson system by constructing explicitly the spin wave function. One finds two selection rules for (a) the total angular momentum J is larger than the maximum angular momentum of the light degree of freedom or smaller than the minimum one; (b) J^C = 1⁺, 2^-, 3⁺, ⋯ if the two mesons are different but belong to the same doublet. This feature may be used to constrain possible strong decay channels.