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

TL;DR

This paper investigates how a triangle singularity mechanism involving a specific resonance contributes to the gamma p to K+ Lambda(1405) reaction, explaining experimental observations and improving theoretical models.

Contribution

It introduces a novel triangle singularity mechanism involving a N* resonance that explains features of the gamma p to K+ Lambda(1405) reaction not accounted for before.

Findings

The triangle singularity produces a peak around 2110 MeV.

Adding this mechanism improves the fit to experimental cross sections.

The mechanism is most significant at cosθ=0.

Abstract

We show the effects of a triangle singularity mechanism for the $\gamma p \to K^+\Lambda(1405)$ reaction. The mechanism has a $N^*$ resonance around 2030 MeV, 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 peak around $\sqrt{s} = 2110$ MeV, and has its largest contribution around cos$\theta=0$. The addition of this mechanism to other conventional ones, leads to a good reproduction of ${\rm d}\sigma/{\rm dcos}\theta$ and the integrated cross section around this energy, providing a solution to a problem encountered in previous theoretical models.