rate of the $f_1(1285)$ and $f_1(1420)$ are the same. []{data-label="Fig:6"}](fig6.eps "fig:"){width="50.00000%"}\

As we can see in Fig. \[Fig:6\], there is a large strength in the cross section built around 1400 MeV induced by the $f_1(1285)$ excitation, which makes it very distinct from the usual shape of the Breit-Wigner distribution for the $f_1(1285)$. It is interesting to see that this cross section is remarkably similar to the one found in Ref. [@Barberis:1998by] (we shall come back to it in the next section to do a comparison with the data). In Ref. [@Barberis:1998by] no explanation was found for this extra strength and it was suggested that it should be the $\pi a_0(980)$ decay mode of the $f_1(1420)$. What we see here is that the peculiar shape of the cross section for this particular channel is a consequence of the triangle diagram of Fig. \[Fig:5\], the mechanism for $\pi a_0(980)$ production from a resonance (the $f_1(1285)$) that is a bound state of $K^*\bar K$, or that couples strongly to $K^*\bar K$ for the purpose (the $f_1(1285)$). The unexpected large strength around 1400 MeV comes from a singularity in the triangle diagram as we discuss in the next section. From that we can conclude 