Penguin diagram explained

In quantum field theory, penguin diagrams are a class of Feynman diagrams which are important for understanding CP violating processes in the standard model. They refer to one-loop processes in which a quark temporarily changes flavor (via a W or Z loop), and the flavor-changed quark engages in some tree interaction, typically a strong one. For the interactions where some quark flavors (e.g., very heavy ones) have much higher interaction amplitudes than others, such as CP-violating or Higgs interactions, these penguin processes may have amplitudes comparable to or even greater than those of the direct tree processes. A similar diagram can be drawn for leptonic decays.^[1]

They were first isolated and studied by Mikhail Shifman, Arkady Vainshtein, and Valentin Zakharov.^{[2] [3]}

The processes which they describe were first directly observed in 1991 and 1994 by the CLEO collaboration.

Origin of the name

John Ellis was the first to refer to a certain class of Feynman diagrams as "penguin diagrams" in a 1977 paper on b-quarks.^[4] The name came about in part due to their shape, and in part due to a legendary bar-room bet with Melissa Franklin. According to John Ellis:^[5]

See also

• John Ellis

Notes and References

1. Web site: Flip Tanedo . Dissecting the Penguin . 2012-03-19 . Quantum Diaries . 2015-04-30 . https://web.archive.org/web/20151125034902/http://www.quantumdiaries.org/2012/03/19/dissecting-the-penguin/ . 2015-11-25 . live .
2. Vainshtein . A. I. . Zakharov . V. I. . Shifman . M. A. . A possible mechanism for the ΔT = 1/2 rule in nonleptonic decays of strange particles . . 22 . 123 . 1975 . 1975ZhPmR..22..123V .
   Translated in Vainshtein . A. I. . Zakharov . V. I. . Shifman . M. A. . A possible mechanism for the ΔT = 1/2 rule in nonleptonic decays of strange particles . . 22 . 55 . 1975 . 1975JETPL..22...55V .
3. . 120 . 2 . 316 . 1977 . 1977NuPhB.120..316S . Asymptotic freedom, light quarks and the origin of the ΔT = 1/2 rule in the non-leptonic decays of strange particles . Shifman . M. A. . Vainshtein . A. I. . Zakharov . V. I. . 10.1016/0550-3213(77)90046-3 .
4. The phenomenology of the next left-handed quarks. 10.1016/0550-3213(77)90374-1. 1977. Ellis. J.. Gaillard. M.K.. Nanopoulos. D.V.. Rudaz. S.. Nuclear Physics B. 131. 2–3. 285–307. 1977NuPhB.131..285E.
5. hep-ph/9510397 . Mikhail Shifman . ITEP Lectures in Particle Physics . 1995.