The K−p→Σ0π0K^-p\to \Sigma^0\pi^0 reaction at low energies in a chiral quark model

A chiral quark-model approach is extended to the study of the $\bar{K}N$ scattering at low energies. The process of $K^-p\to \Sigma^0\pi^0$ at $P_K\lesssim 800$ MeV/c (i.e. the center mass energy $W\lesssim 1.7$ GeV) is investigated. This approach is successful in describing the differential cross sections and total cross section with the roles of the low-lying $\Lambda$ resonances in $n=1$ shells clarified. The $\Lambda(1405)S_{01}$ dominates the reactions over the energy region considered here. Around $P_K\simeq 400$ MeV/c, the $\Lambda(1520)D_{03}$ is responsible for a strong resonant peak in the cross section. The $\Lambda(1670)S_{01}$ has obvious contributions around $P_K=750$ MeV/c, while the contribution of $\Lambda(1690)D_{03}$ is less important in this energy region. The non-resonant background contributions, i.e. $u$-channel and $t$-channel, also play important roles in the explanation of the angular distributions due to amplitude interferences.Comment: 18 pages and 7 figure

η′\eta' photoproduction on the nucleons in the quark model

A chiral quark-model approach is adopted to study the $\gamma p\rightarrow \eta'p$ and $\gamma n\rightarrow \eta' n$. Good descriptions of the recent observations from CLAS and CBELSA/TAPS are obtained. Both of the processes are governed by $S_{11}(1535)$ and $u$ channel background. Strong evidence of an $n=3$ shell resonance $D_{15}(2080)$ is found in the reactions, which accounts for the bump-like structure around $W=2.1$ GeV observed in the total cross section and excitation functions at very forward angles. The $S_{11}(1920)$ seems to be needed in the reactions, with which the total cross section near threshold for the $\gamma p\rightarrow \eta' p$ is improved slightly. The polarized beam asymmetries show some sensitivities to $D_{13}(1520)$, although its effects on the differential cross sections and total cross sections are negligible. There is no obvious evidence of the $P$-, $D_{13}$-, $F$- and $G$-wave resonances with a mass around 2.0 GeV in the reactions.Comment: 10 pages, 9 figure

Charmed baryon strong decays in a chiral quark model

Charmed baryon strong decays are studied in a chiral quark model. The data for the decays of $\Lambda^+_c(2593)$, $\Lambda^+_c(2625)$, $\Sigma^{++,+,0}_c$ and $\Sigma^{+,0}_c(2520)$, are accounted for successfully, which allows to fix the pseudoscalar-meson-quark couplings in an effective chiral Lagrangian. Extending this framework to analyze the strong decays of the newly observed charmed baryons, we classify that both $\Lambda_c(2880)$ and $\Lambda_c(2940)$ are $D$-wave states in the N=2 shell; $\Lambda_c(2880)$ could be $|\Lambda_c ^2 D_{\lambda\lambda}{3/2}^+>$ and $\Lambda_c(2940)$ could be $|\Lambda_c ^2 D_{\lambda\lambda}{5/2}^+>$. Our calculation also suggests that $\Lambda_c(2765)$ is very likely a $\rho$-mode $P$-wave excited state in the N=1 shell, and favors a $|\Lambda_c ^4P_\rho 1/2^->$ configuration. The $\Sigma_c(2800)$ favors being a $|\Sigma_c ^2P_\lambda{1/2}^->$ state. But its being |\Sigma^{++}_c ^4 P_\lambda{5/2}^-> cannot be ruled out.Comment: 22 pages, 16 tables; typos corrected;version to appear in PR

η\eta photoproduction on the quasi-free nucleons in the chiral quark model

A chiral quark-model approach is adopted to study the $\eta$ photoproduction off the quasi-free neutron and proton from a deuteron target. Good descriptions of the differential cross sections, total cross sections and beam asymmetries for these two processes are obtained in the low energy region. For $\gamma p\rightarrow \eta p$, the dominant resonances are $S_{11}(1535)$, $S_{11}(1650)$, $D_{13}(1520)$, $D_{13}(1700)$ and $P_{13}(1720)$. While for the $\gamma n\rightarrow \eta n$ process, the dominant resonances are $S_{11}(1535)$, $S_{11}(1650)$, $D_{13}(1520)$, $D_{15}(1675)$ and $P_{13}(1720)$. Furthermore, the $u$ channel backgrounds have significant contributions to the $\eta$ photoproduction processes. The configuration mixings in the $S_{11}(1535,1650)$ and $D_{13}(1520,1700)$ can be extracted, i.e. $\theta_S\simeq 26^\circ$ and $\theta_D\simeq 21^\circ$. It shows that the narrow bump-like structure around $W= 1.68$ GeV observed in $\gamma n\rightarrow \eta n$ can be naturally explained by the constructive interferences between $S_{11}(1535)$ and $S_{11}(1650)$. In contrast, the destructive interference between $S_{11}(1535)$ and $S_{11}(1650)$ produces the shallow dip around $W= 1.67$ GeV in $\gamma p\rightarrow \eta p$. The $S$ wave interfering behaviors in the proton and neutron reactions are correlated with each other in the quark model framework, and no new exotic nucleon resonances are needed in these two reactions.Comment: 12 pages, 11 figures, helicity amplitudes are added, to be published in PR