1. Size and Structure Mikhail Bashkanov University of Edinburgh UK Nuclear Physics Summer School III

2. Outline Electron scattering Proton form factors Proton size puzzle 2

3. Electron microscopy de Broglie wavelength of probe particle must be ~size of the object you wish to study 3

4. Electrons as waves Scattering process is quantum mechanical 4

5. Classical Fraunhofer Diffraction 5

6. 6

7. Electron scattering. Experiment 7

8. Electron scattering Plane wave approximation for incoming and outgoing electrons Born approximation: interact only once 8

9. Form Factor and charge distribution 9

10. Form Factor and cross-section 10

11. Experiment 11

12. Probing the proton Sachs form factors 12

13. Rosenbluth separation 13

14. Dipole form factor 14

15. Results 15

16. New technique: polarization transfer Longitudinally polarized electron+ Recoil polarimetry Longitudinally polarized electron+ Polarized target 16

17. Data extracted using Rosenbluth separation only 17

18. B Data extracted using polarization transfer only 18

19. All data 19

20. Radiative corrections to single photon exchange 20

21. 21

22. Dipole form factor  proton radius 22

23. Proton Charge radius 23

24. Bohr’s atom 24

25. Hydrogen atom 25

26. Proton radius from hydrogen spectroscopy 26

27. Proton Charge radius 27

28. Proton Charge radius 28

29. Proton Charge radius puzzle 29

30. Lamb shift: status of known corrections VP: vacuum polarization SE: self energy 30

31. Proton radius puzzle: new physics? 31

32. Proton radius puzzle: what’s next? 32

33. Proton 33

34. Nucleon internal structure 34 Valence quarks Sea quarks Gluons

35. Valence quarks 35

36. Sea quarks 36

37. Gluons 37

38. What is inside? 38

39. Proton spin puzzle Proton spin quarks angular momentum gluon spin gluons angular momentum quarks spin Naïve quark model: Reality: 39

40. Conclusion Nucleon structure is complex and complicated A lot of puzzles and a lot of progress New tools, high precision, high accuracy, polarization 40