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Discovering particles - A Brief History
Discovering particles - A Brief History
"Young man, if I could remember the names of these particles, I would have been a botanist!"
Enrico Fermi to Leon Lederman
By 1932 it was accepted that everything around us was made out of three fundamental particles - the proton, electron and neutron. Atoms had a small massive nucleus containing protons and neutrons and it was surrounding by electrons orbiting in discrete energy levels.
06 March 2020 -
Something Weird Just Happened That We Can't Really Explain With Existing Physics - Popular Mechanics article
Researchers propose new physics to explain decay of subatomic particle - phys.org
New Physics Implications of Recent Search for KL→π0ν¯ν at KOTO - Physical Review Letters
Some Background:
Some Background:
The timeline graph below shows when particles were discovered, beginning with the electron (e-) in the late 19th century.
How did advances in technology aid in the discovery of new particles?
Many of these technologies were developed during WW2. War often is an impetus for the development of new technologies. Many people weigh the cost of human lives to the advances in technology.
Antiparticles
Soon after the discovery of the neutron came the discovery of the positron (e+) by Carl Anderson. Antiparticles had been predicted by Paul Dirac. The photograph shows Carl Anderson.
This image shows how the positron was detected using a cloud chamber. The track of the particle is similar to the track for an electron - but in the opposite direction. The track becomes more curved after the particle has passed through a lead plate which is consistent with a particle of the same mass as an electron.
Mesons
Then followed the discovery of mesons in cosmic rays in the late 1940s. The tracks were recorded on emulsion film. The image below shows a pi- meson (π) created at A and then decaying again at B.
The image below shows a K meson decaying into three π mesons at A. One of the π mesons decays at B while the other two go off in opposite directions.
Baryons
In the 1950s and 1960s many more particles were discovered using the bubble chamber, including many known as baryons. The image below is a bubble chamber photograph showing the discovery of the particle called the omega-minus baryon (Ω-).
Quarks
There were so many different varieties of particles discovered in the 1950s and 1960s that this became known as the particle zoo. In 1964 Murray Gell-Mann (1929-2019) suggested that patterns in the particles discovered could be explained if they were made out of smaller particles called quarks. The photograph below shows Murray Gell-Mann.
The term quark is taken from the quote "three quarks for muster mark" in a book by James Joyce.
Baryons like protons and neutrons are made up of 3 quarks, mesons are made up of 2 quarks. The image below shows how some particles can be made out of quarks.
The Standard model
Once you start learning about modern physics, you start to hear about weird particles like quarks and muons and neutrinos. What are all these things? Why are there so many? How do we know they exist? What do they do?
Three Essential Videos:
Three Essential Videos:
The atom now
Our current understanding is that all matter around us consists of atoms made up of the fundamental particles the up quark, the down quark and the electron.
Beyond the IB
Beyond the IB
Fermions
The up and down particles belong to the group called quarks. Electrons and neutrinos belong to the group called leptons. Both quarks and leptons belong to the group called fermions due to the quantum quantity called spin. All fermions have spins = 1/2, 3/2, 5/2 ...
This table lists the quarks and leptons.
Baryons are made up of three quarks. The two most common baryons are the proton and neutron. Baryons also belong to the group called fermions because three quarks in total will also have total spins of 1/2 or 3/2.
This table shows a selection of common baryons.
Unsolved questions
Unsolved questions
Unsolved Questions:
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