3
From Protons and Neutrons to a Zoo of
Particles
Physics research took us one layer down from atoms to nucleus and electrons
and then from the nucleus to its substructures which are protons and neutrons.
Is this the end of the road in the search for fundamental matter or is there
another layer below this? This piqued the curiosity of scientists during the
1950s and 1960s. To appreciate the next stage of the development in the quest
for building blocks of matter, let us summarize the rapid discoveries that were
taking place both in the experimental technology and theoretical analysis. Both
preceeded the breath-taking sequence of events in the 1950s. In this search,
the cosmic ray studies and accelerator experiments went hand in hand, the
first preceding the latter. We do not necessarily follow the developments in
historical sequence in what follows. Rather, we follow them in conceptual
sequence.
3.1 Looking Inside Protons and Neutrons
with High Energy Colliders
To see if there is another layer of matter below the protons and neutrons, we
have to look at distances smaller than their size. How do you probe the inner
substructure of a proton or neutron? The basic idea is not hard to follow. If
you throw a small stone with great force at a rock, the small stone will break
apart and will reveal what is inside it. The faster the stone is thrown, the more
pieces it breaks up into, and the more we see of the inside of it. For subatomic particles, the principle that allows us to probe deep inside is similar,
© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer
Nature Switzerland AG 2021
R. N. Mohapatra, The Neutrino Story: One Tiny Particle’s Grand Role in the Cosmos,
https://doi.org/10.1007/978-3-030-51846-2_3
21
From Protons and Neutrons to a Zoo of
Particles
Physics research took us one layer down from atoms to nucleus and electrons
and then from the nucleus to its substructures which are protons and neutrons.
Is this the end of the road in the search for fundamental matter or is there
another layer below this? This piqued the curiosity of scientists during the
1950s and 1960s. To appreciate the next stage of the development in the quest
for building blocks of matter, let us summarize the rapid discoveries that were
taking place both in the experimental technology and theoretical analysis. Both
preceeded the breath-taking sequence of events in the 1950s. In this search,
the cosmic ray studies and accelerator experiments went hand in hand, the
first preceding the latter. We do not necessarily follow the developments in
historical sequence in what follows. Rather, we follow them in conceptual
sequence.
3.1 Looking Inside Protons and Neutrons
with High Energy Colliders
To see if there is another layer of matter below the protons and neutrons, we
have to look at distances smaller than their size. How do you probe the inner
substructure of a proton or neutron? The basic idea is not hard to follow. If
you throw a small stone with great force at a rock, the small stone will break
apart and will reveal what is inside it. The faster the stone is thrown, the more
pieces it breaks up into, and the more we see of the inside of it. For subatomic particles, the principle that allows us to probe deep inside is similar,
© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer
Nature Switzerland AG 2021
R. N. Mohapatra, The Neutrino Story: One Tiny Particle’s Grand Role in the Cosmos,
https://doi.org/10.1007/978-3-030-51846-2_3
21