The quest for the smallest particles How research

0. Introduction. n World composed of all kinds of different materials n Different properties

1800: Millions of different materials are made of thousands of different molecules, in different

n Different atoms due to different nuclei, which are built of protons and neutrons

n n 9/25/2020 HST 2001 Anderson: 1937, discovery of new particles in the higher

Dealing with this chaos. n Many, many particles where discovered. n Accelerators were built

This scheme leads us again to building blocks on a deeper level: 3 quarks

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

How are the particles ordered now? Hadronen (q) Leptonen (no q) e, µ, e,

But it is not that simple! n There must be a correspondance between the

Questions: Quantum chromo dynamics , QCD, is called the discipline that is doing research

Scale. n So let’s have one more look at the scales at which we

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The quest for the smallest particles. How research on elementary particles evolved during the last 40 years. HST 2001

0. Introduction. n World composed of all kinds of different materials n Different properties n CHAOS n Try to order all these materials n Look at the building blocks of these materials molecules 9/25/2020 HST 2001

1800: Millions of different materials are made of thousands of different molecules, in different combinations. How? CHEMISTRY n Look at the building blocks of these molecules atoms! n Different molecules due to different atoms n Mendeleev : elements ( different atoms) organized in his table. n The logic of the tabel is both chemical and physical n 9/25/2020 HST 2001

n Different atoms due to different nuclei, which are built of protons and neutrons n Niels Bohr. n Neutron discovered in 1932 n Conservation laws lead to the existence of neutrinos and positrons. 9/25/2020 HST 2001

n n 9/25/2020 HST 2001 Anderson: 1937, discovery of new particles in the higher atmosphere Cosmic rays, high energy. More and more « strange » particles. CHAOS again!

Dealing with this chaos. n Many, many particles where discovered. n Accelerators were built to organize collisions to look at the properties of the outcoming particles n They were looking for some order. n First a posteriori attempt: 9/25/2020 HST 2001

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, . . . 9/25/2020 HST 2001

they had to add 3 more quarks : top, bottom and charm. n. This is an example of such a scheme n These particles are built of 3 quarks. 9/25/2020 I’ve been predicted by this scheme, and found later HST 2001

How are the particles ordered now? Hadronen (q) Leptonen (no q) e, µ, e, µ, mesons (2 q) baryons (3 q) spin 3/2 of 1/2 neutrinos Each particle has an antimatter brother 9/25/2020 HST 2001

9/25/2020 HST 2001

But it is not that simple! n There must be a correspondance between the properties of the particles and the properties of quarks. n There are 3 families: why? n Why is there almost no antimatter found? n Why did mass appear at all? n How do these particles interact? 9/25/2020 HST 2001

For example: 9/25/2020 HST 2001

Questions: Quantum chromo dynamics , QCD, is called the discipline that is doing research to give the answers How do these quarks glue together to form protons, neutrons and other particles? n Why are there only particles with 2 or 3 quarks and not more? n Are quarks built of even smaller particles? n. . . n 9/25/2020 HST 2001

Scale. n So let’s have one more look at the scales at which we are working: 9/25/2020 HST 2001