Hi everyone. I have been studying CP violation in kaon systems. I would like to know is someone can explain why, to leading order, strong penguin diagrams (i.e. involving a gluon) only contribute to the [itex]K\to (\pi\pi)_{I=0}[/itex] amplitude, while the isospin 2 amplitude is given by the electro-weak penguins (i.e. involving a photon or a Z boson).(adsbygoogle = window.adsbygoogle || []).push({});

Thank you very much

Edit: I can add more information to the question. Take the gluon penguin diagram. It contains a [itex](\bar ds)[/itex] current which is an SU(3) octet and another current which is a flavor singlet. Therefore, it transform as an [itex](8_L,1_R)[/itex] representation of [itex]SU(3)_L\times SU(3)_R[/itex]. In many books I've found that this implies that it can only carry a change in isospin [itex]\Delta I=1/2[/itex]. Can anyone explain why?

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# Penguin diagrams and CP violation

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