# Hadron interaction via strong yet k mesons decay through weak

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

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)

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.

and yet K Mesons decay through the weak interaction.

Yes.

If my understanding is correct the weak interaction is due to a colour charge?

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

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

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.

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).

Apart from the proton, which is stable, hadrons decay through the week 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.

mfb
Mentor
wolfspirit said:
In terms of the allowed interactions I'm assuming decay is unrelated to an interaction?
A decay involves an interaction of the particle (or particles in the hadron).

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).
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.

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.

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

ChrisVer
Gold Member
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).