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Combined analysis of the $π^-p\rightarrow K^0Λ$, $ηn$ reactions in a chiral quark model

A combined analysis of the reactions $π^-p\rightarrow K^0Λ$ and $ηn$ is carried out with a chiral quark model. The data in the center-of-mass (c.m.) energy range from threshold up to $W\simeq 1.8$ GeV are reasonably described. For $π^-p\rightarrow K^0Λ$, it is found that $N(1535)S_{11}$ and $N(1650)S_{11}$ paly crucial roles near threshold. The $N(1650)S_{11}$ resonance contributes to the reaction through configuration mixing with $N(1535)S_{11}$. The constructive interference between $N(1535)S_{11}$ and $N(1650)S_{11}$ is responsible for the peak structure around threshold in the total cross section. The $n$-pole, $u$- and $t$-channel backgrounds provide significant contributions to the reaction as well. While, for the $π^-p\rightarrow ηn$ process, the "first peak" in the total cross section is dominant by $N(1535)S_{11}$, which has a sizeable destructive interference with $N(1650)S_{11}$. Around $P_π\simeq $ 1.0 GeV/c ($W\simeq 1.7$ GeV), there seems to be a small bump structure in the total cross section, which might be explained by the interference between the $u$-channel and $N(1650)S_{11}$. The $N(1520)D_{13}$ resonance notably affects the angle distributions of the cross sections, although less effects are seen in the total cross section. The role of $P$-wave state $N(1720)P_{13}$ should be further confirmed by future experiments. If $N(1720)P_{13}$ has a narrow width of $Γ\simeq 120$ MeV as found in our previous work by a study of the $π^0$ photoproduction processes, obvious evidence should be seen in the $π^-p\rightarrow K^0Λ$ and $ηn$ processes as well.