Isospin and a possible interpretation of the newly observed X(1576)

Recently, the BES collaboration observed a broad resonant structure X(1576) with a large width being around 800 MeV and assigned its $J^{PC}$ number to $1^{--}$. We show that the isospin of this resonant structure should be assigned to 1. This state might be a molecule state or a tetraquark state. We study the consequences of a possible $K^*(892)$-${\bar \kappa}$ molecular interpretation. In this scenario, the broad width can easily be understood. By using the data of $B(J/\psi\to X\pi^0)\cdot B(X\to K^+K^-)$, the branching ratios $B(J/\psi\to X\pi^0)\cdot B(X\to \pi^+\pi^-)$ and $B(J/\psi\to X\pi^0)\cdot B(X\to K^+K^-\pi^+\pi^-)$ are further estimated in this molecular state scenario. It is shown that the $X\to \pi^+\pi^-$ decay mode should have a much larger branching ratio than the $X\to K^+K^-$ decay mode has. As a consequence, this resonant structure should also be seen in the $J/\psi\to \pi^+\pi^-\pi^0$ and $J/\psi\to K^+K^-\pi^+\pi^-\pi^0$ processes, especially in the former process. Carefully searching this resonant structure in the $J/\psi\to \pi^+\pi^-\pi^0$ and $J/\psi\to K^+K^-\pi^+\pi^-\pi^0$ decays should be important for understanding the structure of X(1567).Comment: 5 pages, ReVTeX4, 3 figures. Version accepted for publication as a brief report in Phys. Rev.

Relativistic mean-field approximation with density-dependent screening meson masses in nuclear matter

The Debye screening masses of the $\sigma$, $\omega$ and neutral $\rho$ mesons and the photon are calculated in the relativistic mean-field approximation. As the density of the nucleon increases, all the screening masses of mesons increase. It shows a different result with Brown-Rho scaling, which implies a reduction in the mass of all the mesons in the nuclear matter except the pion. Replacing the masses of the mesons with their corresponding screening masses in Walecka-1 model, five saturation properties of the nuclear matter are fixed reasonably, and then a density-dependent relativistic mean-field model is proposed without introducing the non-linear self-coupling terms of mesons.Comment: 14 pages, 3 figures, REVTEX4, Accepted for publication in Int. J. Mod. Phys.

Chromo-polarizability and pipi final state interaction

The chromo-polarizability of a quarkonium state is a measure of the amplitude of the $E1$-$E1$ chromo-electric interaction of the quarkonium with soft gluon fields and can be measured in the heavy quarkonium decays. Based on the chiral unitary approach, formulas with modification caused by the $S$ wave $\pi\pi$ final state interaction (FSI) for measuring the chromo-polarizabilities are given. It is shown that the effect of the $S$ wave $\pi\pi$ FSI is very important in extracting chromo-polarizabilities from the experimental data. The resultant values with the FSI are reduced to about 1/3 of those determined without the FSI. The consequences of the FSI correction in the $J/\psi$-nucleon scattering near the threshold are also discussed. The estimated lower bound of the total cross section is reduced from about 17 mb to 2.9 mb, which agrees with the experimental data point and is compatible with the previously estimated values in the literature. In order to understand the interaction of heavy quarkonia with light hadrons at low energies better and to obtain the chromo-polarizabilities of quarkonia accurately, more data should be accumulated. This can be done in the $J/\psi \to \pi^+\pi^-l^+l^-$ decay at BES-III and CLEO-c and in the $\Upsilon \to \pi^+\pi^-l^+l^-$ decay at B factories.Comment: 5 pages, 3 figures, ReVTeX4. Version accepted for publication in Phys. Rev.