1. Spin is everywhere… Why do cats always land on their feet? Evidence for dark matter in the universe…

2. Even they were puzzled… W. Pauli N. Bohr  … but this is purely classic!

3. Spin in quantum mechanics…… O. Klein G. Uhlenbeck A. Goudsmit P. Ehrenfest (1925): “This is a good idea. Your idea may be wrong, but since both of you are so young without any reputation, you would not loose anything making a stupid mistake.” …. spin as a fundamental property of elementary particles:

4. Proton spin The value: S = The original idea: The applications: Example: MRI Alzheimer’s disease © VUMC Alzheimercentrum

5. The origin of proton spin European Muon Collaboration (EMC) @ CERN (1985): ZEUS and H1 experiments @ DESY (early ’90’s): Quarks carry only a small fraction of the proton spin In the proton abundant quark-antiquark pairs and gluons are found. gluon Quark-antiquark pair

6. Search the carriers of proton spin ½ = ½  q +  G + L q Three possible sources:  quark-antiquarks (sea quarks)  gluons  orbital momentum Mathematically: ~ 30% ?? (Valence  Sea Quarks?)

7. HERA e-p collider at DESY The HERMES experiment at HERA: 6.2 km circumference ring, 27 GeV e + & 920 GeV p’s

8. Outlook Spin is everywhere The origin of proton spin: –gluons & orbital motion Importance QCD physics: The of mass and spin of the constituents of the visible universe are rooted in QCD dynamics