QCD Form Factors and Hadron Helicity Non-Conservation

Abstract

Recent data for the ratio $R(Q)=Q{F}_2(Q^2)/F_1(Q^2)$ shocked the community by disobeying expectations held for 50 years. We examine the status of perturbative QCD predictions for helicity-flip form factors. Contrary to common belief, we find there is no rule of hadron helicity conservation for form factors. Instead the analysis yields an inequality that the leading power of helicity-flip processes may equal or exceed the power of helicity conserving processes. Numerical calculations support the rule, and extend the result to the regime of laboratory momentum transfer $Q^2$. Quark orbital angular momentum, an important feature of the helicity flip processes, may play a role in all form factors at large $Q^2$, depending on the quark wave functions.

25 pages, 5 figures

References in corpus (13)

• The ratio of proton's electric to magnetic form factors measured by polarization transfer
• Measurement of GEp/GMp in ep -> ep to Q2 = 5.6 GeV2
• Electromagnetic structure of the deuteron
• Nonforward parton densities and soft mechanism for form factors and wide-angle Compton scattering in QCD
• Perturbative QCD Analysis of the Nucleon's Pauli Form Factor F_2(Q^2)
• The Spin Structure of the Nucleon in the Asymptotic Limit
• Precision Measurement of the Neutron Spin Asymmetry $A_1^n$ and Spin-Flavor Decomposition in the Valence Quark Region
• The Role of Color Neutrality in Nuclear Physics--Modifications of Nucleonic Wave Functions
• Quantum Color Transparency and Nuclear Filtering
• $Q^2$ Independence of $Q{F}_2/F_1$, Poincare Invariance and the Non-Conservation of Helicity
• A Critical Analysis of the Proton Form Factor with Sudakov Suppression and Intrinsic Transverse Momentum
• Hadron Helicity Violation in Exclusive Processes: Quantitative Calculations in Leading Order QCD
• The perturbative proton form factor reexamined

Cited by in corpus (26)

• Unraveling hadron structure with generalized parton distributions
• Is the low-l microwave background cosmic?
• Baryons as relativistic three-quark bound states
• Nucleon Electromagnetic Form Factors
• Proton elastic form factor ratios to $Q^2$ = 3.5 GeV${}^2$ by polarization transfer
• Dispersion analysis of the nucleon form factors including meson continua
• Nucleon electromagnetic form factors
• The Spin Structure of the Proton
• Final Analysis of Proton Form Factor Ratio Data at ${\mathbf{Q}}^2=4.0$, 4.8 and 5.6 GeV${}^2$
• Electromagnetic Form Factors of the Nucleon and Compton Scattering
• Nucleon electromagnetic form factors from the covariant Faddeev equation
• Low Q^2 measurements of the proton form factor ratio $m{u}_p{G}_E/G_M$
• Polarization Transfer Observables in Elastic Electron Proton Scattering at $Q^2=$2.5, 5.2, 6.8, and 8.5 GeV${}^2$
• Role of diquark correlations and the pion cloud in nucleon elastic form factors
• The shape of the nucleon
• Baryon Octet Electromagnetic Form Factors in a confining NJL model
• A description of the ratio between electric and magnetic proton form factors by using space-like, time-like data and dispersion relations
• Prospects for e+e- physics at Frascati between the phi and the psi
• Global Analysis of hadronic two-body B decays in the perturbative QCD approach
• Asymptotic behavior of nucleon electromagnetic form factors in time-like region
• The Generalized Counting Rule and Oscillatory Scaling
• Uncovering the Scaling Laws of Hard Exclusive Hadronic Processes in a Comprehensive Endpoint Model
• The Dirac Form Factor Predicts the Pauli Form Factor in the Endpoint Model
• Elastic nucleon form factors
• Proton and neutron form factors with quark orbital excitations
• Unpolarized nucleon structure studies utilizing polarized electromagnetic probes