1. The quest for the smallest particles.
The quest for the smallest particles.
How research on elementary particles evolved during the last 40 years.
Wim Peeters

2. 0. Introduction. World composed of all kinds of different materials
Different properties
CHAOS
Try to order all these materials
Look at the building blocks of these materials molecules
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3. Look at the building blocks of these molecules atoms!
1800: Millions of different materials are made of thousands of different molecules, in different combinations How? CHEMISTRY
Look at the building blocks of these molecules
atoms!
Different molecules due to different atoms
Mendeleev : elements ( different atoms) organized in his table.
The logic of the tabel is both chemical and physical
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4. Conservation laws lead to the existence of neutrinos and positrons.
Different atoms due to different nuclei, which are built of protons and neutrons
Niels Bohr.
Neutron discovered in 1932
Conservation laws lead to the existence of neutrinos and positrons.
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5. Anderson: 1937, discovery of new particles in the higher atmosphere
Cosmic rays, high energy.
More and more « strange » particles.
CHAOS again!
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6. Dealing with this chaos.
Many, many particles where discovered.
Accelerators were built to organize collisions to look at the properties of the outcoming particles
They were looking for some order.
First a posteriori attempt:
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7. This scheme leads us again to building blocks on a deeper level:
3 quarks were needed at first: up, down en strange; later on they discovered more particles, with other properties, to order these too,...
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8. they had to add 3 more quarks :top, bottom and charm.
This is an example of such a scheme
These particles are built of 3 quarks.
I’ve been predicted by this scheme, and found later
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9. How are the particles ordered now?
Hadronen (q)
Leptonen (no q)
e, µ, 
e, µ,  
mesons (2q)
baryons (3q)
spin 3/2 of 1/2
neutrinos
Each particle has an antimatter brother
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10.
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11.
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12. But it is not that simple!
There must be a correspondance between the properties of the particles and the properties of quarks.
There are 3 families: why?
Why is there almost no antimatter found?
Why did mass appear at all?
How do these particles interact?
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13. For example:
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14. Quantum chromo dynamics , QCD, is called the discipline that is doing research to give the answers
Questions:
How do these quarks glue together to form protons, neutrons and other particles?
Why are there only particles with 2 or 3 quarks and not more?
Are quarks built of even smaller particles?
...
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15. Scale.
So let’s have one more look at the scales at which we are working:
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