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# Fermi, Enrico

Fermi, Enrico, 1901-54, American physicist, b. Italy. He studied at Pisa, Göttingen, and Leiden, and taught physics at the universities of Florence and Rome. He contributed to the early theory of beta decay and the neutrino and to quantum statistics. For his experiments with neutrons he was awarded the 1938 Nobel Prize in Physics. Fermi's wife, Laura, was Jewish, and the family did not return to Fascist Italy after the journey to Stockholm to receive the Nobel award, but continued on to the United States. Fermi was professor of physics at Columbia Univ. (1939-45) and at the Univ. of Chicago (1946-54). He created the first self-sustaining chain reaction in uranium at Chicago in 1942 and worked on the atomic bomb at Los Alamos. Later he contributed to the development of the hydrogen bomb and served on the General Advisory Committee of the Atomic Energy Commission, which named him to receive its first special award (\$25,000) shortly before his death. Fermi was outstanding as an experimenter, theorist, and teacher. He wrote Elementary Particles (1951). In 1954 the chemical element fermium of atomic number 100 was named for him. Publication of his Collected Papers (ed. by Edoardo Amaldi et al.) was begun in 1962.

See L. Fermi, Atoms in the Family (1954, repr. 1988); biography by E. Segrè (1970).

In physics, Fermi's interaction is an old explanation of the weak force, proposed by Enrico Fermi. Four fermions directly interact with one another. For example, this interaction is directly able to split a neutron (or two down-quarks and an up-quark) to an electron, antineutrino and a proton (or two up-quarks and a down-quark).

Tree Feynman diagrams describe the interaction remarkably well. Unfortunately, loop diagrams cannot be calculated reliably because Fermi's interaction is not renormalizable. The solution is to replace the four-fermion contact interaction by a more complete theory (see UV completion) — an exchange of a W boson or a Z boson as explained in the electroweak theory. The electroweak theory is renormalizable.

Before the electroweak theory and the Standard Model were constructed, George Sudarshan and Robert Marshak, and also independently Richard Feynman and Murray Gell-Mann were able to determine the correct tensor structure (vector minus axial vector, V−A) of the four-fermion interaction.

## Fermi constant

The strength of Fermi's interaction is given by the Fermi constant $G_F$. In modern terms,

$frac\left\{G_\left\{F\right\}\right\}\left\{\left(hbar c\right)^3\right\}=frac\left\{sqrt\left\{2\right\}\right\}\left\{8\right\}frac\left\{g^\left\{2\right\}\right\}\left\{m_\left\{W\right\}^\left\{2\right\}\right\}=1.16637\left(1\right)times10^\left\{-5\right\}textrm\left\{GeV\right\}^\left\{-2\right\}$

Here $g$ is the coupling constant of the weak interaction, and $m_W$ is the mass of the W boson.

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