Narrow Results

The cross-sections of $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}\psi (3686)$ and $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c^{+}{\mathrm{\Lambda }}_c^{-}$ have been measured by Belle experiment. A resonance $Y(4660)$ is observed in ${\pi }^{+}{\pi }^{-}\psi (3686)$ decay mode, while another resonance $Y(4630)$ is observed in ${\mathrm{\Lambda }}_c^{+}{\mathrm{\Lambda }}_c^{-}$ decay mode. The two resonances $Y(4660)$ and $Y(4630)$’s parameters are consistent with each other, so a combined fit is performed to the two cross-sections assuming $Y(4660)$ and $Y(4630)$ are same resonance. $Y(4660)$’s parameters are determined to be $M_{Y(4660)}=(4632.0\pm 7.8\pm 3.1)\mathrm{\text{MeV}}/c^2$, ${\mathrm{\Gamma }}_{Y(4660)}=(69.8\pm 13.5\pm 3.8)\mathrm{\text{MeV}}$, where the first uncertainties are statistical and the second systematic. The ratio $\frac{{ℬ}(Y(4660)\to {\mathrm{\Lambda }}_c^{+}{\mathrm{\Lambda }}_c^{-})}{{ℬ}(Y(4660)\to {\pi }^{+}{\pi }^{-}\psi (3686))}$ is also obtained and it indicates that $Y(4660)$’s main decay modes may be ${\mathrm{\Lambda }}_c^{+}{\mathrm{\Lambda }}_c^{-}$. We determine the lower limit of its leptonic decay width of around 40 eV, which can be compared with the theoretical expectations of different models.

In this paper, we assume $X(5568)$ exist and study mass spectrum of $X(5568)$ resonance and its hypothetical charmed partner, $X_c$, by artificial neural network method. The obtained predictions are compared with the experimental data and results of other theoretical works.

We discuss the possible interpretation of X(3872) as a DD* hadronic molecule with J^PC = 2^-+. Using the phenomenological Lagrangian approach, we studied its radiative and strong decay properties. We find that our model with about 97.6% isospin zero component explains the existing data nicely. We predict the partial widths of the radiative and strong decays of X(3872) and show that the measurement of the ratio may signal the nature of X(3872).

We propose a new mechanism, named as the initial single chiral particle emission mechanism, to explain the charged Z_b(10610) and Z_b(10650) observed in the ϒ(5S) → π⁺π^-ϒ(nS), π⁺π^-h_b(mP), (n = 1 ~ 3, m = 1, 2) processes. After successfully interpreting the charge Z_b structures, we extend this mechanism to study the process of the dipion transitions between the higher charmonia/charmonium-like state and the lower charmonia. In these transitions process, we predict two charmonium analogs of the charged Z_b. After the observations of Z_c(3900) by the BESIII and the Belle Collaborations, we reproduce the dipion and the J/ψπ invariant mass distributions simultaneously with the initial single chiral particle emission mechanism. In addition, we predict some enhancements in the J/ψK invariant mass spectra in the dikaon decay of the higher charmonium and the charmonium like 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.

We present that the X(3872) could be represented as a dynamically generated state in the extended Friedrichs scheme, in which the ratio of “elementariness” and “compositeness” of the different components in the X(3872) is about $Z_{c\overline{c}}:X_{{\overline{D}}^0{D}^{0*}}:X_{D^{+}{D}^{-*}}:X_{{\overline{D}}^{*}{D}^{*}}=1:\left(2.67\sim 8.85\right):\left(0.45\sim 0.46\right):0.04$. Furthermore, its decays to π⁰ and a P-wave charmonium χ_cJ state with J = 0; 1, or 2, J/ψπ⁺π⁻, and J/ψπ⁺π⁻π⁰ could be calculated out with the help of Barnes-Swanson model. The isospin breaking effects is easily understood in this scheme. This calculation also shows that the decay rate of X(3872) to χ_c1π⁰ is much smaller than its decay rate to J/ψπ⁺π⁻.

Recently observed heavy quark exotic XYZ mesons stimulated heated discussions about their structures. In the molecule picture, we discuss the spin of the heavy quark pair in an S-wave meson-antimeson state, whose value is either 1 or 0. We find two rules that the spin is only 1 in the heavy quark limit. From the conservation of the spin, one may analyze the charmonium products from strong decays. The selection rules give constraints on the products.