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We perform a Faddeev calculation for the three mesons system, $phi K bar{K}$, taking the interaction between two pseudoscalar mesons and between a vector and a pseudoscalar meson from the chiral unitary approach. We obtain a neat resonance peak around a total mass of 2150 MeV and an invariant mass for the $K bar{K}$ system around 970 MeV, very close to the $f_0(980)$ mass. The state appears in I=0 and qualifies as a $phi f_0(980)$ resonance. We enlarge the space of states including $phi pi pi$, since $pi pi$ and $K bar{K}$ build up the $f_0$ (980), and find moderate changes that serve to quantify theoretical uncertainties. No state is seen in I=1. This finding provides a natural explanation for the recent state found at BABAR and BES, the X(2175), which decays into $phi f_0(980)$.
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We investigate the decay and the production mechanism of the resonance X(1812) recently observed in the $jptogamma X(1812), X(1812)toomegaphi$ at BESII. The decay widths of $X(1812)toetaeta$,$ etaeta$,$ omegaphi$,$ K^+K^-$,$ rho^+rho^-$, $ omegaomega$,$ K^{*+}K^{*-}$ and $pi^+pi^-$ are evaluated based on the scenario of the X(1812) as a candidate of $(ksks)$ molecule. It turns out that the quark exchange mechanism plays an important role in the understanding of the large decay width for the $X(1812)toomegaphi$. It is also found that the decay widths for $X(1812)toetaeta$ and $etaeta$ are enhanced by the quark exchange mechanism. These channels are suggested to be the tools to test the molecular scenario in experiment. The branching fraction of $Br(Xtoomegaphi)$ is evaluated to be about 4.60%. Searches for additional evidence about the X(1812) in $jp$ radiative decays are reviewed. In the molecular scenario, the X(1812) production rate is also evaluated to be $Gamma(jptogamma X)/Gamma(jptogamma K^{*+}K^{*-})=2.13^{+7.41}_{-1.85}$, which is close to the measured value $2.83pm0.92$.
A dynamical coupled-channel study of K* K*bar state with isospin 0 and omega phi state is performed within both the chiral SU(3) quark model and the extended chiral SU(3) quark model by solving a resonating group method (RGM) equation. The model parameters are taken from our previous work, which gave a satisfactory description of the energies of the octet and decuplet baryon ground states, the binding energy of the deuteron, the nucleon-nucleon (NN) scattering phase shifts, and the hyperon-nucleon (YN) cross sections. The results show that the interactions of K* K*bar states are attractive, which consequently result in K* K*bar bound states with the binding energies of about 10-70 MeV, and contrarily, no omega phi bound state is obtained. The channel coupling effect of K* K*bar and omega phi is found to be considerably large, which makes the binding of K* K*bar 5-45 MeV deeper. The plausible interpretation of f_0(1710) and X(1812) being K* K*bar dominated states is briefly discussed.
We report on self-consistent calculations of single-K^- nuclear states and multi-Kbar nuclear states in 12C, 16O, 40Ca and 208Pb within the relativistic mean-field (RMF) approach. Gradient terms motivated by the p-wave resonance Sigma(1385) are found to play a secondary role for single-K^- nuclear systems where the mean-field concept is acceptable. Significant contributions from the Kbar N -> pi Lambda conversion mode, and from the nonmesonic Kbar NN -> YN conversion modes which are assumed to follow a rho^2 density dependence, are evaluated for the deep binding-energy range of over 100 MeV where the decay channel Kbar N -> pi Sigma is closed. Altogether we obtain K^- total decay widths of 50-100 MeV for binding energies exceeding 100 MeV in single-K^- nuclei. Multi-Kbar nuclear calculations indicate that the binding energy per Kbar meson saturates upon increasing the number of Kbar mesons embedded in the nuclear medium. The nuclear and Kbar densities increase only moderately and are close to saturation, with no indication of any kaon-condensation precursor.
We evaluate the $sigma$ exchange contribution to the $bar{K}Ntobar{K}N$ scattering within a chiral unitary approach. We show that the chiral transition potentials for $pi pi to K bar{K}$ in the $t$-channel lead to a $sigma$ contribution that vanishes in the $bar{K}$ forward direction and, hence, would produce a null $sigma$ exchange contribution to the $K^-$ optical potential in nuclear matter in a simple impulse approximation. This is a consequence of the fact that the leading order chiral Lagrangian gives an I=0 $pipito Kbar{K}$ amplitude proportional to the squared momentum transfer, $q^2$. This finding poses questions on the meaning or the origin of $sigma$ exchange potentials used in relativistic mean field approaches to the $K^-$ nuclear selfenergy. This elementary $sigma$ exchange potential in $bar{K}Ntobar{K}N$ is compared to the Weinberg-Tomozawa term and is found to be smaller than present theoretical uncertainties but will be relevant in the future when aiming at fitting increasingly more accurate data.
The real and imaginary parts of the bar K^0 d scattering length are extracted from the bar K^0 d mass spectrum obtained from the reaction pp to d bar K^0 K^+ measured recently at the Cooler Synchrotron COSY at Julich. We extract a new limit on the K^- d scattering length, namely Im a le 1.3 fm and |Re a| le 1.3 fm. The limit for the imaginary part of the K^- d scattering length is supported by data on the total K^- d cross sections.
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