Role of a triangle singularity in the $\gamma p ightarrow K^+ \Lambda(1405)$ reaction

摘要

We show the effects of a triangle singularity mechanism for the $\gamma p \toK^+\Lambda(1405)$ reaction. The mechanism has a $N^*$ resonance around 2030MeV, which decays into $K^* \Sigma$. The $K^*$ decays to $K^+ \pi$, and the$\pi \Sigma$ merge to form the $\Lambda(1405)$. This mechanism produces a peakaround $\sqrt{s} = 2110$ MeV, and has its largest contribution aroundcos$\theta=0$. The addition of this mechanism to other conventional ones, leadsto a good reproduction of ${\rm d}\sigma/{\rm dcos}\theta$ and the integratedcross section around this energy, providing a solution to a problem encounteredin previous theoretical models.