K⁻ p scattering and hyperon excitations in a chiral quark model

A chiral quark-model approach is employed to study the N scattering at low energies. The processes of K⁻p → σ⁰π⁰, Λπ⁰ and ⁰n at P_K ≤ 800 MeV/c (i.e. the center mass energy W ≤ 1.7 GeV) are investigated. The analysis shows that the Λ(1405)S₀₁ dominates the processes K⁻p → σ⁰π⁰, ⁰n in the energy region considered here. Around P_K ∊ 400 MeV/c, the Λ(1520)D₀₃ is responsible for a strong resonant peak in the cross section of K⁻p → σ⁰π⁰ and ⁰n. To reproduce the data, an unexpectedly large coupling for Λ(1520)D₀₃ to KN is needed. In contrast, the coupling for Λ(1670)S₀₁ to KN appears to be weak, which could be due to configuration mixings between Λ(1405)S₀₁ and Λ(1670)S₀₁. By analyzing K⁻p → Λπ⁰, evidences for two low mass S-wave states, σ(1480) S₁₁ and σ(1560) S₁₁, seem to be available. With these two states, the reaction K⁻p → ⁰n can also be described well. However, it is difficult to understand the low masses of σ(1480) S₁₁ and σ(1560) S₁₁. The s-channel amplitudes for K⁻p → Λπ⁰ are also larger than the naive quark model expectations. The non-resonant background contributions, i.e. t-channel and/or u-channel, also play important roles in the explanation of the angular distributions due to amplitude interferences.