Why is the Strong Force Responsible for Pi+ + Proton -> K+ + X?

[zanyzoya]

Please can you help,
I have seen an exam question which asks which interaction is responsible for the following ...
Pi⁺ + proton >>>>> K⁺ + unknown particle X

The options for the answer include both the weak and the strong force. The actual answer is the strong force. What I would like to know is why the strong force is responsible rather than the weak force?
Many thanks
Zoya

 

[Orodruin]

The strong force is significantly stronger than the weak force. Thus, if a process can occur through both, the dominant contribution will generally come from strong interactions.

In order for this to not be the case, the process must be forbidden in strong interactions.

 

[zanyzoya]

Thanks for that. And am I right in thinking that either the strong or weak force could be responsible as only hadrons are involved, ie no leptons exist on either side of the equation? If there were leptons involved on either side then only the weak force could be responsible and not the strong?

 

[zanyzoya]

for example in beta decay the weak force is responsible even though there are no leptons on the lhs and only on the rhs.

 

[Orodruin]

Thanks for that. And am I right in thinking that either the strong or weak force could be responsible as only hadrons are involved, ie no leptons exist on either side of the equation? If there were leptons involved on either side then only the weak force could be responsible and not the strong?

That is one part of it, but the strong interactions also conserve many more things, such as quark flavor. There are generally several things to check. Of course, with X being an unknown particle you really cannot check quark flavor conservation.

 

[zanyzoya]

Ah I see, thanks. Later on we are asked to find the strangeness of particle X. I guess strangeness wouldn't be conserved during the weak interaction and therefore you could not answer this question. Hence another reason the interaction must be due to the strong force.

 

[Orodruin]

Some weak interactions do conserve strangeness. The main reason it is a strong interaction is that it can be.