Triangle mechanisms in the build up and decay of the $N^*(1875)$

Abstract

We have studied the $N^*(1875) (3/2^-)$ resonance with a multichannel unitary scheme, considering the $Δπ$ and $Σ^* K$, with their interaction extracted from chiral Lagrangians, and then have added two more channels, the $N^*(1535) π$ and $N σ$, which proceed via triangle diagrams involving the $Σ^* K$ and $Δπ$ respectively in the intermediate states. The triangle diagram in the $N^*(1535) π$ case develops a singularity at the same energy as the resonance mass. We determine the couplings of the resonance to the different channels and the partial decay widths. We find a very large decay width to $Σ^* K$, and also see that, due to interference with other terms, the $N σ$ channel has an important role in the $ππ$ mass distributions at low invariant masses, leading to an apparently large $N σ$ decay width. A discussion is done, justifying the convenience of an experimental reanalysis of this resonance to the light of the findings of the paper, using multichannel unitary schemes.