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 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 process
In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are us ...
es. 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,
Arkady Vainshtein, and Valentin Zakharov.
The processes which they describe were first directly observed in 1991 and 1994 by the
CLEO collaboration.
Origin of the name
John Ellis John Ellis may refer to:
Academics
*John Ellis (scrivener) (1698–1791), English political writer
*John Ellis (naturalist) (1710–1776), English botanical illustrator
*John Ellis (physicist, born 1946), British theoretical physicist at CERN
* Jo ...
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 depart ...
. According to John Ellis:
See also
*
John Ellis John Ellis may refer to:
Academics
*John Ellis (scrivener) (1698–1791), English political writer
*John Ellis (naturalist) (1710–1776), English botanical illustrator
*John Ellis (physicist, born 1946), British theoretical physicist at CERN
* Jo ...
References
{{DEFAULTSORT:Penguin Diagram
Electroweak theory
Diagrams