# Relation strength interaction and decay time

1. May 19, 2007

### da_willem

There is this characteristic time associated with the decay of particles; ~10^-16s for electromagnetic decay, ~10^-23s for strong decay and >10^-13s for weak decay. Now I know that the decay time is to first order inversely proportional to the coupling constant squared (from a first order Feynman diagram with only a vertex contribution). So from this point of view I 'understand' why decay via strong interactions go faster than via weak interactions, but how can one see this physically?

Short times for virtual particles correspond to high energies by the hup, and I've seen the relation between the virtual particle mass and the interaction range, but why do interactions with exchange of virtual massless gluons go faster than those with exchange of photons which goes faster than the exchange of massive intermediate vector bosons?!

Last edited: May 19, 2007
2. May 21, 2007

### Meir Achuz

1. $$\alpha(EM)$$, and $$\alpha(QCD)$$ each vary with energy.
At energies for typical decays (~100 MeV)
$$\alpha(QCD)\sim 100\alpha(EM)$$.

2. The effective weak coupling for typical decays
$$\sim \alpha(EM)(M_p/M_W)^2$$.

Last edited: May 21, 2007