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Silversonic
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Homework Statement
(1) Indicate whether the following process (if possible) occurs due to the strong, weak or electromagnetic interation.
[itex] \pi^{-} p → \pi^{-} \pi^{+} n [/itex]
(3) Sketch Quark flow diagrams for the following, stating whether it's due to EM, weak or strong interaction;
[itex] K^{*+} → K^{+} \pi^{0} [/itex]
The K*+ is an excited state of the K+, it has the same quark composition.
The Attempt at a Solution
I'm having a hard time understanding whether you can know the first question is a strong or weak interaction. My answer tells me that because it's dealing only with hadrons, it is therefore the strong interaction. However, the weak interaction (W+-) is able to couple to quark pairs (e.g. [itex] u [/itex] and [itex]\bar{d}[/itex]). The emission of a W boson also changes the quark flavour.
So in the first interaction, wouldn't it be possible for the [itex] \pi^{-} [/itex] to just be an "observer" particle, while an up quark in the proton decays via the weak interaction into a down quark (changing the proton into a neutron), and thus this W+ boson subsequently couple to a [itex] u [/itex] and [itex]\bar{d}[/itex] pair creating the [itex] \pi^{+} [/itex] meson?
The second question also has me stumped. It shows the one of the quarks of the [itex] K^{*+} [/itex] meson decaying via the strong interaction, emitting a gluon which subsequently produces the [itex] \pi^{0} [/itex]. However, why can't this process happen exactly the same way with electromagnetic interaction? One of the quarks of the [itex] K^{*+} [/itex] decays via electromagnetic interaction, emitting a virtual photon and this virtual photon subsequently couples to a quark, antiquark pair producing the [itex] \pi^{0} [/itex]. I don't see any violation at all? So why must it be the strong force? Hell, the same could happen with the weak interaction using the Z boson.
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