Penguin decays of B mesons

Penguin, or loop, decays of B 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 b → sγ and B → K*γ and gluonic penguins B → Kπ, B⁺ → ωK⁺ and B → η′K, and their implications for the standard model and new physics. We conclude by exploring the future prospects for penguin physics.