58
R. N. Mohapatra
G F , is called Fermi’s constant (the subscript F being short form for Fermi). It
was a major step forward in understanding the neutrino as well as the weak
force.
8.1 Fermi Theory of Beta Decay
Enrico Fermi was born in 1901 in Rome, Italy, to Alberto and Ida de Gattis
Fermi. His older brother died when he was 14. This had a profound effect on
him. His parents diverted his attention to physics to keep him engaged. He
went to the Scuola Normale Superiore in Pisa for his university education and
graduated in 1922. He then worked with Max Born in Gottingen for some
time. He came to America in 1938 after receiving the Nobel Prize.
Enrico Fermi wrote his theory of beta decay involving the neutrino in 1933,
using the language of Quantum Field Theory. He followed Dirac’s approach
to light emission and his own earlier paper on the “Quantum Theory of Light”
in Reviews of Modern Physics. He wrote out an interaction where the neutron
under the influence of weak force converts spontaneously to a proton, electron,
and a neutrino. He wrote this paper after attending the Solvay conference of
1933, where the prime topics were the neutron, neutrino, and beta decay. This
conference was attended by Bohr, Chadwick, Rutherford, Pauli, Heisenberg,
Dirac among others. After coming from the conference, Fermi used the formulation with creation and annihilation operators, introduced by Jordan and
Wigner a few years earlier, to write a theory for beta decay. The revolutionary
nature of Fermi theory was that unlike in light emission where the emitting
electron remains an electron after emission, the electron and the neutrino get
created out of a neutron converting to a proton. This theory gave the first
real method to quantitatively deal with the process of beta decay, as well as
the neutrino. The story from a paper by C. N. Yang [105] is that Jordan and
Wigner, who invented the Quantum Field Theory for spin half particles like
the neutrino, did not know how to create a theory for the production of the
neutrino in beta decay. Wigner called Fermi’s beta decay theory paper Fermi’s
biggest contribution to physics. When Yang asked Wigner why he thought the
Fermi paper was so revolutionary, Wigner apparently said [105] “No, no, you
do not understand the impact it produced at the time. Von Neumann and I
had been thinking about beta-decay for a long time, as did everybody else. We
simply did not know how to create an electron inside a nucleus.”
Nowadays, Fermi’s theory looks so simple that one wonders how it was not
done earlier. But what Fermi did was a major breakthrough in thinking at
that time. Fermi first submitted his “tentative” (Fermi’s quotes, see below)
R. N. Mohapatra
G F , is called Fermi’s constant (the subscript F being short form for Fermi). It
was a major step forward in understanding the neutrino as well as the weak
force.
8.1 Fermi Theory of Beta Decay
Enrico Fermi was born in 1901 in Rome, Italy, to Alberto and Ida de Gattis
Fermi. His older brother died when he was 14. This had a profound effect on
him. His parents diverted his attention to physics to keep him engaged. He
went to the Scuola Normale Superiore in Pisa for his university education and
graduated in 1922. He then worked with Max Born in Gottingen for some
time. He came to America in 1938 after receiving the Nobel Prize.
Enrico Fermi wrote his theory of beta decay involving the neutrino in 1933,
using the language of Quantum Field Theory. He followed Dirac’s approach
to light emission and his own earlier paper on the “Quantum Theory of Light”
in Reviews of Modern Physics. He wrote out an interaction where the neutron
under the influence of weak force converts spontaneously to a proton, electron,
and a neutrino. He wrote this paper after attending the Solvay conference of
1933, where the prime topics were the neutron, neutrino, and beta decay. This
conference was attended by Bohr, Chadwick, Rutherford, Pauli, Heisenberg,
Dirac among others. After coming from the conference, Fermi used the formulation with creation and annihilation operators, introduced by Jordan and
Wigner a few years earlier, to write a theory for beta decay. The revolutionary
nature of Fermi theory was that unlike in light emission where the emitting
electron remains an electron after emission, the electron and the neutrino get
created out of a neutron converting to a proton. This theory gave the first
real method to quantitatively deal with the process of beta decay, as well as
the neutrino. The story from a paper by C. N. Yang [105] is that Jordan and
Wigner, who invented the Quantum Field Theory for spin half particles like
the neutrino, did not know how to create a theory for the production of the
neutrino in beta decay. Wigner called Fermi’s beta decay theory paper Fermi’s
biggest contribution to physics. When Yang asked Wigner why he thought the
Fermi paper was so revolutionary, Wigner apparently said [105] “No, no, you
do not understand the impact it produced at the time. Von Neumann and I
had been thinking about beta-decay for a long time, as did everybody else. We
simply did not know how to create an electron inside a nucleus.”
Nowadays, Fermi’s theory looks so simple that one wonders how it was not
done earlier. But what Fermi did was a major breakthrough in thinking at
that time. Fermi first submitted his “tentative” (Fermi’s quotes, see below)