Photoproduction of $Λ(1405)$ with the two-pole structure

We investigate the $Λ(1405,1/2^-)\equivΛ^*$ photoproduction off the proton target, i.e. $γp\to K^+Λ^*$, considering explicitly its two-pole structure, the higher ($Λ^*_H:\,1430\,\mathrm{MeV}$) and lower ($Λ^*_L:\,1390\,\mathrm{MeV}$) mass-pole contributions, suggested by the chiral-unitary model (ChUM) approaches. For this purpose, we construct a two-body process model, which mimics the Dalitz process, $γp\to K^+πΣ$, assuming that the mass of $Λ^*$ as the invariant mass of $π$ and $Σ$, i.e. $M_{Λ^*}\sim M_{πΣ}$. We employ the effective Lagrangian method with the tree-level Born approximation, using the gauge-invariant prescription for the phenomenological form factors. We provide the numerical results for the energy and angular dependences, $π$-$Σ$ invariant-mass distribution, and so on. It turns out that the model parameters determined from ChUM reproduce the experimental data qualitatively well, supporting the two-pole structure. Moreover, the nucleon resonance contribution near the threshold plays an important role to describe the data.

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