I'm looking at a physics textbook for A-level and in the book it states that kaons are only affected by the strong force and the electromagnetic force. Isn't this incorrect? Aren't kaons affected by the weak force as well?
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2Which textbook? – Qmechanic Dec 31 '23 at 07:30
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1AQA Physics, Oxford University Press, A level Year 1 and AS, Author Jim Breithaupt. Page 21 – S Paul Dec 31 '23 at 17:15
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You are correct. All of the quarks and leptons of the Standard Model, and their composites, participate in the strong, electromagnetic, and weak interactions. The leptons, which lack color charge, don't participate in the strong interaction; the neutrinos, which lack electric charge, don't participate in the electromagnetic interaction either. But a particle which doesn't participate in the weak interaction isn't a member of the Standard Model.
The kaon, a hadron with one unit of strangeness, decays via the charged weak current into zero-strangeness pions and/or leptons.
Note that some people will try to tell you that the weak interaction isn't properly a "force." They're wrong, but the approximation is useful, because the interaction is, to use the unfortunately punny technical term, much weaker or feebler than electromagnetism or the strong interaction.
rob
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That all Standard Model particles participate in the weak interaction is only true if by 'particle' you mean 'mass eigenstate'. This is not a very good way of talking about the SM, which is really clearly formulated using Weyl fermions. The crucial thing about the weak interaction is that it is chiral---only the 'left-handed' quarks and leptons interact via the weak interaction. This is only 8/15 of the degrees of freedom in each generation, not all of them. – SethK Dec 31 '23 at 10:23
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That's correct for the charged current. For the neutral current, the chiral projection operator $(1-\gamma^5)$ gets a $\sin^2\theta_W$ in it, so there is a nontrivial interaction between the right-handed fermions and the $Z$. In either case, fermion chirality is a little bit of a deep dive for this question about the first table in a textbook for high school students. – rob Jan 01 '24 at 15:13
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This text book is really a shame. As you had detected correctly, the kaons feel also the weak force, e.g. in the decay mode $K^+ \to \mu^+ \nu_\mu$ being mediated by the exchange of a virtual $W^+$ boson. But this is not the only error in this table. Also the pions interact weakly, in particular the dominant decay mode of the charged pion, $\pi^+ \to \mu^+ \nu_\mu$, is a weak decay. It is also not correct that the neutral pion does not feel the electromagnetic interaction (as suggested in the table), as it decays electromagnetically via $\pi^0 \to \gamma \gamma$. Also the neutron can interact with the electromagnetic field via its magnetic moment.
Hyperon
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