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.[citation needed]
- ^ Flip Tanedo (2012-03-19). "Dissecting the Penguin". Quantum Diaries. Archived from the original on 2015-11-25. Retrieved 2015-04-30.
- ^ Vainshtein, A. I.; Zakharov, V. I.; Shifman, M. A. (1975). "A possible mechanism for the ΔT = 1/2 rule in nonleptonic decays of strange particles". Pisma Zh. Eksp. Teor. Fiz. 22: 123. Bibcode:1975ZhPmR..22..123V.
Translated in Vainshtein, A. I.; Zakharov, V. I.; Shifman, M. A. (1975). "A possible mechanism for the ΔT = 1/2 rule in nonleptonic decays of strange particles". JETP Letters. 22: 55. Bibcode:1975JETPL..22...55V. - ^ Shifman, M. A.; Vainshtein, A. I.; Zakharov, V. I. (1977). "Asymptotic freedom, light quarks and the origin of the ΔT = 1/2 rule in the non-leptonic decays of strange particles". Nuclear Physics B. 120 (2): 316. Bibcode:1977NuPhB.120..316S. doi:10.1016/0550-3213(77)90046-3.