<s>
In	O
quantum	O
field	O
theory	O
,	O
penguin	B-Application
diagrams	I-Application
are	O
a	O
class	O
of	O
Feynman	O
diagrams	O
which	O
are	O
important	O
for	O
understanding	O
CP	O
violating	O
processes	O
in	O
the	O
standard	B-General_Concept
model	I-General_Concept
.	O
</s>
<s>
They	O
refer	O
to	O
one-loop	O
processes	O
in	O
which	O
a	O
quark	B-Operating_System
temporarily	O
changes	O
flavor	O
(	O
via	O
a	O
W	O
or	O
Z	O
loop	O
)	O
,	O
and	O
the	O
flavor-changed	O
quark	B-Operating_System
engages	O
in	O
some	O
tree	O
interaction	O
,	O
typically	O
a	O
strong	O
one	O
.	O
</s>
<s>
For	O
the	O
interactions	O
where	O
some	O
quark	B-Operating_System
flavors	O
(	O
e.g.	O
,	O
very	O
heavy	O
ones	O
)	O
have	O
much	O
higher	O
interaction	O
amplitudes	O
than	O
others	O
,	O
such	O
as	O
CP-violating	O
or	O
Higgs	O
interactions	O
,	O
these	O
penguin	O
processes	O
may	O
have	O
amplitudes	O
comparable	O
to	O
or	O
even	O
greater	O
than	O
those	O
of	O
the	O
direct	O
tree	O
processes	O
.	O
</s>
<s>
The	O
processes	O
which	O
they	O
describe	O
were	O
first	O
directly	O
observed	O
in	O
1991	O
and	O
1994	O
by	O
the	O
CLEO	B-Algorithm
collaboration	O
.	O
</s>
<s>
John	O
Ellis	O
was	O
the	O
first	O
to	O
refer	O
to	O
a	O
certain	O
class	O
of	O
Feynman	O
diagrams	O
as	O
"	O
penguin	B-Application
diagrams	I-Application
"	O
in	O
a	O
1977	O
paper	O
on	O
b-quarks	O
.	O
</s>
