Light Front Calculations of Nucleon Form

Factors - shapes of the proton G A Miller, UW

• Experimental progress JLAB• Model: relativistic quarks, π cloud,

symmetry-aided phenomenology• Electromagnetic form factors

• Shapes of proton, spin of proton

• Connect with lattice QCD

Definitions

Expectations- Pre JlabExpectations- Pre Jlab

GE/GM

Q2

QF2 /F1

Q2

QF2/F1GE/GM

Jlab Jlab

Implement Relativity

Impulse Approximation

Wave function

1995 Frank, Jennings, Miller

Ratio of Pauli to Dirac Form Factors 1995

Relativistic Explanation

Neutron Electric Form Factor

Ratio of Pauli to Dirac Form Factors 2003

Two More Form Factors Needed

Model exists• Lower components OAM

• Shape of proton

• Spin dependent densities SDD non-rel

• Relativistic SDD H atom

• Proton

Shapes of the proton

Spin density operator: (r-rp)n

Canted ferromagnetic structure of UNiGe high magnetic fields

• Neutron magnetic scattering

• Neutron, B, crystal

PRB65, 144429

LFCBM and LATTICE FORM FACTORS

• H. H. Matevosyan, GAM, AW Thomas

• Lattice results described using LFCBM with parameters taken as analytic functions of lattice quark mass

• Extrapolate back to physical regime

• Form factors look like data

• First attempt to relate lattice QCD with

form factors that depend on Q2

Reproduce Lattice QCDSF data

Extrapolate to physical, predict

Summary

• Phenomenological model –three quark plus pion cloud- of nucleon respects Lorentz invariance and chiral

symmetry

• Describes form factor data pretty well

• Has some connection with lattice/fundamental theory

Extras follow

High Q2

How proton holds together

• pQCD

Feynman

Non perturbative∞ gluon exch

Compton scattering same modelRelativistic Massive Quarks