Role of the Possible Σ*(1/2-) in the Λp->ΛpΠ0 Reaction
Study of the spectrum of the Σ(1193) excited states, Σ*, with isospin I = 1 and strangeness S = −1 is one of the most important issues in hadronic physics. The Λp->ΛpΠ0 reaction is a very good isospin 1 filter for studying Σ* resonances decaying to ΛΠ, and provides a useful tool for testing Σ* baryon models.
Researchers at the Institute of Modern Physics, Chinese Academy of Sciences (IMP) study the Λp->ΛpΠ0 reaction near threshold within an effective Lagrangian method and the isobar model. The production process is described by single-pion and single-kaon exchange. In addition to the role played by the Σ*(1385) resonance of spin-parity JP = 3/2+, the effects of a newly proposed Σ*(JP = 1/2−) state with mass and width around 1380 MeV and 120 MeV are investigated. It is found that the model leads to a good description of the experimental data on the total cross section (see Fig. 1) of the Λp->ΛpΠ0 reaction by including the contributions from the possible Σ*(1/2−) state. However, the theoretical calculations by considering only theΣ*(1385) resonance fail to reproduce the experimental data, especially for the enhancement close to the reaction threshold, which indicates that the Λp->ΛpΠ0 data support the existence of this Σ*(1380) state, and more accurate data for this reaction can be used to improve our knowledge of the Σ*(1380) properties. The present calculation offers some important clues for the mechanisms of the Λp->ΛpΠ0 reaction and is the first effort at studying the role of the Σ*(1380) state in a relevant reaction.
The related results have been published in Phys. Rev. C 90, 055204 (2014).
Fig. 1：Contributions of Σ*(1385) resonance (dashed line), Σ*(1380) state (dotted line), nucleon pole (dash-dotted line), and Σ(1193) pole (dash-dot-dotted line) to the total cross sections vs the beam momentum plab for the Λp->ΛpΠ0 reaction. Their total contribution is shown by the solid line.