Triangle singularity in the J/ψ→ϕπ+a0−(π−η) , ϕπ−a0+(π+η) decays

Abstract

We study the J/ψ→ϕπ+a0(980)−(a0−→π−η) decay, evaluating the double mass distribution in terms of the π−η and π+a0− invariant masses. We show that the π−η mass distribution exhibits the typical cusp structure of the a0(980) seen in recent high statistics experiments, and the π+a0− spectrum shows clearly a peak around Minv(π+a0−)=1420  MeV, corresponding to a triangle singularity. When integrating over the two invariant masses we find a branching ratio for this decay of the order of 10−5, which is easily accessible in present laboratories. We also call attention to the fact that the signal obtained is compatible with a bump experimentally observed in the ηπ+π− mass distribution in the J/ψ→ϕηπ+π− decay and encourage further analysis to extract from there the ϕπ+a0− and ϕπ−a0+ decay modes. Published by the American Physical Society 2024