1. The problem statement, all variables and given/known data The J/Ψ has mass 3097 MeV, width 87 keV and equal branching ratios of 6% to e+e− and µ+µ− ﬁnal states. What would you expect for these branching ratios if the J/Ψ decayed only electromagnetically? What does this tell you about the “strength” of the strong interaction in this decay? 2. Relevant equations Branching function = Width/Sum of all Widths Don't know whether this will be useful or not but: Lifetime of u = 2.2*10-6 Mass of u = 106MeV/c2 3. The attempt at a solution I don't really know what to do, I don't understand branching functions that well and I'm not even sure if the question requires me to calculate anything, i'm confused. I know that strong forces dominate and that the average lifetime for strong interactions is ~10-24seconds whilst EM ~ 10-18. This isn't homework really, this is just revision for an examination I have tomorrow. If somebody could just explain this briefly, that would help immensely.