III Proton Size and Structure Mikhail Bashkanov University

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

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

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

Electrons as waves Scattering process is quantum mechanical 4

Classical Fraunhofer Diffraction 5

6

Electron scattering. Experiment 7

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

Form Factor and charge distribution � 9

Form Factor and cross-section � 10

Experiment 11

Probing the proton � Sachs form factors 12

Rosenbluth separation 13

Dipole form factor � 14

Results 15

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

Data extracted using Rosenbluth separation only 17

Data extracted using polarization transfer only B 18

All data 19

corrections to single photon exchange 20

Proton radius puzzle 21

� Dipole form factor proton radius 22

Proton Charge radius 23

Bohr’s atom 24

Hydrogen atom 25

Proton radius from hydrogen spectroscopy 26

Proton Charge radius 27

Proton Charge radius 28

Proton Charge radius puzzle 29

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

Proton radius puzzle: new physics? � 31

Proton radius puzzle: what’s next? � 32

Proton 33

Nucleon internal structure Valence quarks Gluons Sea quarks 34

Valence quarks 35

Sea quarks 36

Gluons 37

What is inside? 38

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

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