The quest for the smallest The quest for the smallest particles.particles.

How research on elementary particles How research on elementary particles evolved during the last 40 years.evolved during the last 40 years.

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0. Introduction.0. Introduction.

World composed of all kinds of World composed of all kinds of different materialsdifferent materials

Different propertiesDifferent properties CHAOSCHAOS Try to order all these materialsTry to order all these materials Look at the building blocks of Look at the building blocks of

these materials moleculesthese materials molecules

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1800: Millions of different materials are made 1800: Millions of different materials are made of thousands of different molecules, in different of thousands of different molecules, in different combinations. How? CHEMISTRYcombinations. How? CHEMISTRY

Look at the building blocks of these moleculesLook at the building blocks of these molecules atoms!atoms! Different molecules due to different atomsDifferent molecules due to different atoms Mendeleev : elements ( different atoms) Mendeleev : elements ( different atoms)

organized in his table.organized in his table. The logic of the tabel is both chemical and The logic of the tabel is both chemical and

physicalphysical

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Different atoms due to different Different atoms due to different nucleinuclei, which are built of protons , which are built of protons and neutronsand neutrons

Niels Bohr.Niels Bohr. Neutron discovered in 1932Neutron discovered in 1932 Conservation laws lead to the Conservation laws lead to the

existence of neutrinos and existence of neutrinos and positrons.positrons.

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Anderson: 1937, Anderson: 1937, discovery of new discovery of new particles in the particles in the higher atmospherehigher atmosphere

Cosmic rays, high Cosmic rays, high energy.energy.

More and more More and more « strange » « strange » particles.particles.

CHAOS again!CHAOS again!

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Dealing with this chaos.Dealing with this chaos.

Many, many particles where Many, many particles where discovered.discovered.

Accelerators were built to organize Accelerators were built to organize collisions to look at the properties collisions to look at the properties of the outcoming particlesof the outcoming particles

They were looking for some order.They were looking for some order. First a posteriori attempt:First a posteriori attempt:

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3 quarks were needed at first: up, down en strange; later on they discovered more particles, with other properties, to order these too,...

This scheme leads us again to building blocks on a deeper level:

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they had to add 3 more quarks :top, top, bottom and charm.bottom and charm.

These particles These particles are built of 3 are built of 3 quarks.quarks.

This is an This is an example of example of such a such a schemescheme

I’ve been predicted by this scheme, and found

later

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How are the particles ordered How are the particles ordered now?now?

neutrinosneutrinos

Hadronen (q)Hadronen (q)

e, µ, e, µ, ee, , µµ, ,

Leptonen (no q)Leptonen (no q)

mesons (2q)mesons (2q) baryons baryons (3q)(3q)spin 3/2 of 1/2spin 3/2 of 1/2

Each particle has an antimatter brother

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But it is not that simple!But it is not that simple!

There must be a correspondance There must be a correspondance between the properties of the particles between the properties of the particles and the properties of quarks.and the properties of quarks.

There are 3 families: why?There are 3 families: why? Why is there almost no antimatter Why is there almost no antimatter

found?found? Why did mass appear at all?Why did mass appear at all? How do these particles interact?How do these particles interact?

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For example:For example:

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Questions:Questions:

How do these quarks glue How do these quarks glue together to form protons, together to form protons, neutrons and other particles?neutrons and other particles?

Why are there only particles Why are there only particles with 2 or 3 quarks and not with 2 or 3 quarks and not more?more?

Are quarks built of even Are quarks built of even smaller particles?smaller particles?

......

Quantum chromo dynamics , QCD, is called the discipline that is doing

research to give the answers

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So let’s have So let’s have one more look one more look at the scales at the scales at which we at which we are working:are working:

Scale.Scale.