Role of the possible Σ*(1/2-) state in the Λp → Λpπ0 reaction

The Lambda p -> Lambda p pi(0) reaction near threshold is studied within an effective Lagrangian method. The production process is described by single-pion and single-kaon exchange. In addition to the role played by the Sigma*(1385) resonance of spin-parity J(P) = 3/2(+), the effects of a newly proposed Sigma* (J(P) = 1/2(-)) state with mass and width around 1380 MeV and 120 MeV are investigated. We show that our model leads to a good description of the experimental data on the total cross section of the Lambda p -> Lambda p pi(0) reaction by including the contributions from the possible Sigma* (1/2(-)) state. However, the theoretical calculations by considering only the Sigma*(1385) resonance fail to reproduce the experimental data, especially for the enhancement close to the reaction threshold. On the other hand, it is found that the single-pion exchange is dominant. Furthermore, we also demonstrate that the angular distributions provide direct information of this reaction, hence could be useful for the investigation of the existence of the Sigma*(1/2(-)) state and may be tested by future experiments.