Weak nuclear Vs Strong nuclear

[jpa]

How do you determine in a particle interaction which force is responsible?

For example

a K- meson is found to decay into three charged pi mesons what force is involved?

The answer here is a weak interaction but why?

 

[Bill_K]

Two reasons. First, the kaon lifetime is about 10^-8 sec, and strong interactions typically occur in 10^-23 sec. Second, strangeness is changed in the kaon decay and the strong interaction conserves it.

 

[jpa]

So could we say that strangeness number is the key.
If its conserved then the interaction was via the strong nuclear else its weak nuclear!

 

[kaksmet]

The key in this case, but it cannot be generally stated that that is the case.

A safe way to figure this out is to see what quarks/leptons exist in initial and final state and then write down feynman diagrams describing the transition from one into the other. If it can occur via the strong interaction, it will, if not then the weak interaction has a chance.

If there is a quark(anti-quark) which exist in only the initial state OR only the final state without its corresponding anti-quark(quark) the weak interaction has to play a part.

Hope that helps.