# Hadron interaction via strong yet k mesons decay through weak

1. Aug 21, 2014

### wolfspirit

Hi,
I have been getting a little confused; the text book (and from what i can see on-line) are saying that Hadrons only interact through the strong interaction (along with the electromagnetic force if charged Q) and yet K Mesons decay through the weak interaction. If my understanding is correct the weak interaction is due to a colour charge? since k mesons (or any hadrons for that matter) don't have a colour charge then how can the decay through the weak interaction?

I have been really struggling to get my head round this so any help would be greatly appreciated!

Many thanks
Ryan

2. Aug 21, 2014

### The_Duck

This is false, so probably you have misinterpreted what you read. All quarks and leptons can interact via the weak force; since hadrons are made of quarks they can also interact via the weak force.

Since the weak interaction is weak, usually its effect is negligible except in processes that can *only* occur via the weak interaction. For example, K mesons cannot decay through the electromagnetic interaction or the strong interaction, because the electromagnetic and strong interaction both conserve strange quark number. The weak interaction can violate conservation of strangeness and therefore K mesons can decay through the weak interaction, and only through the weak interaction.

Yes.

No. Color charge is the charge associated with the strong force.

3. Aug 21, 2014

### wolfspirit

I have re read the book and it makes a lot more sense now however this is a few things I'm still not 100% sure about.
so just to get this straight in my mind: to quote the book;
"hadrons interact through strong interaction and through the electromagnetic interaction if charged. Apart from the proton, which is stable, hadrons decay through the week interaction."

"Leptons interact through the week interaction and through the electromagnetic interaction if charged."

In terms of the allowed interactions I'm assuming decay is unrelated to an interaction?

In addition can hadrons actually interact with the weak force or just decay through the weak force?
Many thanks
Ryan

4. Aug 21, 2014

### The_Duck

Sounds like the book is talking about things like scattering here; scattering of hadrons is indeed dominated by the strong and electromagnetic interactions and the effect of the weak interaction, while nonzero, is negligible (even the electromagnetic interaction is mostly negligible compared to the strong interaction).

This is true for many hadrons, but there are also hadrons which decay via the strong interaction (e.g. the rho meson) or via the electromagnetic interaction (e.g. the J/psi meson). Usually, hadrons decay via the strongest force that allows the decay.

5. Aug 21, 2014

### Staff: Mentor

A decay involves an interaction of the particle (or particles in the hadron).

The weak interaction is relevant in processes like the production of single top quarks (where it is necessary) and in some of the production processes for the Higgs boson and other particles.

6. Aug 21, 2014

### The_Duck

Yes, I suppose what I've said is only valid at low energies. At high enough energies the weak interaction is not weak.

7. Aug 21, 2014

### ChrisVer

Additionally, in general the hadrons can indeed interact in scattering processes through weak interactions. This is how the neutrino detectors actually try to work. For example the scattering of protons with neutrinos and so on (a whole variety of methods, depending on the neutrinos and what you want to study).