In
quantum field theory
In theoretical physics, quantum field theory (QFT) is a theoretical framework that combines classical field theory, special relativity, and quantum mechanics. QFT is used in particle physics to construct physical models of subatomic particles and ...
, penguin diagrams are a class of
Feynman diagrams
In theoretical physics, a Feynman diagram is a pictorial representation of the mathematical expressions describing the behavior and interaction of subatomic particles. The scheme is named after American physicist Richard Feynman, who introduce ...
which are important for understanding
CP violating processes in the
standard model
The Standard Model of particle physics is the theory describing three of the four known fundamental forces (electromagnetism, electromagnetic, weak interaction, weak and strong interactions - excluding gravity) in the universe and classifying a ...
. They refer to
one-loop processes in which a
quark
A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. All commonly o ...
temporarily changes
flavor
Flavor or flavour is either the sensory perception of taste or smell, or a flavoring in food that produces such perception.
Flavor or flavour may also refer to:
Science
*Flavors (programming language), an early object-oriented extension to Lis ...
(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
lepton
In particle physics, a lepton is an elementary particle of half-integer spin ( spin ) that does not undergo strong interactions. Two main classes of leptons exist: charged leptons (also known as the electron-like leptons or muons), and neutr ...
ic decays.
They were first isolated and studied by
Mikhail Shifman
Mikhail "Misha" Arkadyevich Shifman (russian: Михаи́л Арка́дьевич Ши́фман; born 4 April 1949) is a theoretical physicist (high energy physics), formerly at Institute for Theoretical and Experimental Physics, Moscow, Ida ...
,
Arkady Vainshtein
Arkady Vainshtein (russian: Аркáдий Иóсифович Вайнштéйн; born 24 February 1942) is a Russian and American Professor Emeritus of Theoretical physics who was awarded Pomeranchuk Prize (2005) and Sakurai Prize (1999) for theor ...
, and Valentin Zakharov.
The processes which they describe were first directly observed in 1991 and 1994 by the
CLEO Cleo may refer to:
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* ''Cleo'' (magazine), an Australian magazine established in 1972, now active in Indonesia, Malaysia, Singapore, and Thailand
* Cleo (group), a South Korean girl group formed in 1999
* ''Cleo'' (play), by Lawren ...
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.
The name came about in part due to their shape, and in part due to a legendary bar-room bet with
Melissa Franklin
Melissa Eve Bronwen Franklin (born September 30, 1956) is a Canadian experimental particle physicist and the Mallinckrodt Professor of Physics at Harvard University. In 1992, Franklin became the first woman to receive tenure in the Physics depar ...
. According to John Ellis:
See also
*
John Ellis
References
{{DEFAULTSORT:Penguin Diagram
Electroweak theory
Diagrams