Penguin, or loop, decays of mesons induce effective flavor-changing neutral currents, which are forbidden at tree level in the standard model. These decays give special insight into the CKM matrix and are sensitive to non–standard-model effects. In this review, we give a historical and theoretical introduction to penguins and a description of the various types of penguin processes: electromagnetic, electroweak, and gluonic. We review the experimental searches for penguin decays, including the measurements of the electromagnetic penguins γ and *γ and gluonic penguins π, + → ω+ and → η′, and their implications for the standard model and new physics. We conclude by exploring the future prospects for penguin physics.

Keyword(s): charmlessCP violationloop

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  • Article Type: Review Article
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