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
- Slides: 40