The $Ω_c \to π^+ \, (π^0,\, η)\, πΞ^*$ reactions and the two $Ξ(1820)$ states

Abstract: We have studied the $\Omega_c \to \pi^+ (\pi^0, \eta) \pi \Xi^*$ decays, where the final $\pi \Xi^*$ comes from the decay of two resonances around the nominal $\Xi(1820)$, which are generated from the interaction of coupled channels made of a pseudoscalar and a baryon of the decuplet. The $\pi \Xi^*$ mass distributions obtained in the six different reactions studied are quite different and we single out four of them, which are free of a tree level contribution, showing more clearly the effect of the resonances. The lower mass resonance is clearly seen as a sharp peak, but the higher mass resonance manifests itself through an interference with the lower one that leads to a dip in the mass distribution around $1850 \, {\rm MeV}$. Such a feature is similar to the dip observed in the $s$-wave $\pi \pi$ cross section around the $980 \, {\rm MeV}$ coming from the interference of the $f_0(500)$ and $f_0(980)$ resonances. Its observation in coming upgrades of present facilities will shed light on the existence of these two resonances and their nature.