Evidence for a narrowD03state inK−p→ηΛnear threshold

Abstract

Recently, we reported a theoretical study on the $K^- p \to \eta \Lambda$ reaction near threshold by using an effective Lagrangian approach. It was found that the description of angular distribution data measured by the Crystal Ball Collaboration needs a $D_{03}$ resonance with mass $M=1668.5\pm 0.5$ MeV and total decay width $\Gamma=1.5\pm 0.5$ MeV, which is not the conventional $\Lambda$(1690) or other $\Lambda$ state listed in the Particle Data Group book. In the present work, we study the $\Lambda$ polarization in the $K^- p \to \eta \Lambda$ reaction within the same framework. The results show that the existence of this narrow $D_{03}$ state is also compatible with current $\Lambda$ polarization data and that the more accurate $\Lambda$ polarization data at $P_{K^-}=735$MeV can offer further evidence for the existence of this resonance. Furthermore, the role of the $\Lambda(1690)$ resonance in this reaction is also discussed.