Poetry of Physics and the Physics of Poetry

242 The Poetry of Physics and The Physics of Poetry

for light. There are two types of neutrinos associated with the electron,
the νe and the νμ. We shall return to the muon and the other leptons when
we will discuss the weak interaction in greater detail.
The disappointment over the lack of interaction of the muon with
nucleons was very keen. However, in 1947 another study of cosmic rays
by Powell, Lattes, and Occhialini revealed the existence of a second
intermediate mass particle, the pion or π meson. This new particle had all
the features required by Yukawa’s theory. It interacts strongly with
nucleons, it has three charge states, π+, πo and π– and finally its mass of
140 MeV can explain the 10-13 cm range of the nuclear force.
Our image of the neutron and the proton changes as a result of
Yukawa’s model of the strong interaction. The proton and neutron can
no longer be considered stable particles. They are continuously in
flux, changing their state every 10-23 seconds, perpetually surrounded
by a seething, surging cloud of mesons. The neutron and the proton are
also continually exchanging roles, each becoming the other by
exchanging the appropriately charged π meson. For the proton the
following transformations take place, p → n + π+ → p → p + πo → p. It
represents the proton transforming itself into a neutron and a positively
charged pion and then back into a proton and then into a proton and a πo
and then back again to a proton. These transformations may also be
represented by Feynman diagrams like the ones introduced to designate
the scattering of charged particles through virtual photon exchange. This
transformation would appear in the language of Feynman diagrams as
follows:

Elementary Particles, Quarks and Quantum Chromodynamics 231

the &e and the &μ. We shall return to the muon and the other leptons when

we will discuss the weak interaction in greater detail.

The disappointment over the lack of interaction of the muon with

nucleons was very keen. However, in 1947 another study of cosmic rays

by Powell, Lattes, and Occhialini revealed the existence of a second

in termediate mass particle, the pion or ' meson. This new particle had all

the features required by Yukawa’s theory. It interacts strongly with

nucleons, it has three charge states, '+, 'o and '- and finally its mass of

140 MeV can explain the 10-13 cm range of the nuclear force.

Our image of the neutron and the proton changes as a result of

Yukawa’s model of the strong interaction. The proton and neutron can no

longer be considered stable particles. They are continuously in flux,

changing their state every 1 0 -23 seconds, perpetually surrounded by a

seething, surging cloud of mesons. The neutron and the proton are also

continually exchanging roles, each becoming the other by exchanging the

appropriately charged ' meson. For the proton the following

transformations take place, p % n + '+ % p % p + 'o % p. It represents

the proton transforming itself into a neutron and a positively charged

pion and then back into a proton and then into a proton and a 'o and then

back again to a proton. These transformations may also be represented by

Feynman diagrams like the ones introduced to designate the scattering of

charged particles through virtual photon exchange. This transformation

would appear in the language of Feynman diagrams as follows:

Figure 23.1

The neutron undergoes a similar transformation turning into a proton and

a negatively charged pion and then back into a neutron and then into a

neutron and a neutral pion and finally back into a neutron, i.e.,

n % p + '- % n % n + 'o % n.

The proton and neutron are continually emitting and reabsorbing

mesons. The mesons can never wander more than 10-13 cm from the

proton or else they will no longer be masked by the uncertainty principle

Fig. 24.1

The neutron undergoes a similar transformation turning into a proton and
a negatively charged pion and then back into a neutron and then into a
neutron and a neutral pion and finally back into a neutron, i.e.,

n → p + π– → n → n + πo → n.