$f_1(1285)$ decays into $a_0(980)π^0$, $f_0(980)π^0$ and isospin breaking

Abstract

We evaluate the decay width for the processes $f_1(1285) \to π^0 a_0(980)$ and $f_1(1285) \to π^0 f_0(980)$ taking into account that all three resonances are dynamically generated from the meson-meson interaction, the $f_1(1285)$ from $K^* \bar K -c.c$ and the $a_0(980)$, $f_0(980)$ from $πη, K \bar K$ and $ππ, K \bar K$ respectively. We use a triangular mechanism similar to that of the $η(1405) \to ππη$, which provides a decay width for $f_1(1285) \to π^0 a_0(980)$ with a branching fraction of the order of 30%, in agreement with experiment. At the same time we evaluate the decay width for the isospin forbidden $f_1(1285) \to π^0 f_0(980)$, which appears when we consider different masses for the charged and neutral kaons, and show that it is much more suppressed than in the $η(1405) \to ππη$ case, but gives rise to a narrow shape of the $π^+ π^-$ distribution similar to the one found in the $η(1405) \to ππη$ decay.