Why Is the Process Epsilon Meson to Eta Meson Forbidden?

[dsdsuster]

Does anyone have any idea why the process epsilon meson to eta meson is forbidden?
bb' --> cc'

Mass Energies
9.3 GeV --> 3.0 GeV

The solution set simply says that this is kinematically forbidden. It seems to me that in the center of momentum frame the products can have whatever momentum necessary to makeup for the smaller mass energy.

Thanks!

 

[Simon Bridge]

I get 548MeV/c^2 for the eta meson and 958MeV/c^2 for it's antiparticle.

Upsilon meson 9.4GeV/c^2

For $Y\rightarrow \eta$ to happen, you need the Y to decay ... so, presumably, you'd get something to happen to the excess energy ... maybe just a very fast eta right? Or maybe other particles appear ... but there is more to it than just matching the raw energies.

The way to understand this sort of thing is to draw out the diagram for the decay: what exactly is the process.