175 research outputs found

### 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.

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