Hadron structure at low Q^2

Abstract

This review deals with the structure of hadrons, strongly interacting many-body systems consisting of quarks and gluons. These systems have a size of about 1 fm, which shows up in scattering experiments at low momentum transfers $Q$ in the GeV region. At this scale the running coupling constant of Quantum Chromodynamics (QCD), the established theory of the strong interactions, becomes divergent. It is therefore highly intriguing to explore this theory in the realm of its strong interaction regime. However, the quarks and gluons can not be resolved at the GeV scale but have to be studied through their manifestations in the bound many-body systems, for instance pions, nucleons and their resonances. The review starts with a short overview of QCD at low momentum transfer and a summary of the theoretical apparatus describing the interaction of hadrons with electrons and photons. In the following sections we present the experimental results for the most significant observables studied with the electromagnetic probe: form factors, polarizabilities, excitation spectra, and sum rules. These experimental findings are compared and interpreted with various theoretical approaches to QCD, such as phenomenological models with quarks and pions, dispersion relations as a means to connect observables from different experiments, and, directly based on the QCD lagrangian, chiral perturbation theory and lattice gauge theory.

55 pages, 47 figures, review

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• Electromagnetic excitation of the Delta(1232)-resonance
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• Global analysis of proton elastic form factor data with two-photon exchange corrections
• Chiral Perturbation Theory and Baryon Properties
• Charge Density of the Neutron
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• Strange Quark Contributions to Parity-Violating Asymmetries in the Forward G0 Electron-Proton Scattering Experiment
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• Photo- and Electroproduction of Eta Mesons
• Virtual Compton Scattering and Generalized Polarizabilities of the Proton
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• Search for Quadrupole Strength in the Electro-excitation of the Delta(1232)
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• Neutron charge form factor at large $q^2$
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• Induced pseudoscalar coupling of the proton weak interaction
• Coulomb Corrections to Elastic Electron-Proton Scattering and the Proton Charge Radius
• Precision Electromagnetic Structure of Octet Baryons in the Chiral Regime
• Investigation of the conjectured nucleon deformation at low momentum transfer
• Measurement of the vector analyzing power in elastic electron-proton scattering as a probe of double photon exchange amplitudes
• Status on nucleon electromagnetic form factors
• Electromagnetic transition form factors of negative parity nucleon resonances
• The GDH Sum Rule and Related Integrals
• Strange Electric Form Factor of the Proton
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• Chiral Effective-Field Theory in the Delta(1232) Region: Pion Electroproduction on the Nucleon
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• The nucleon electromagnetic form factors from Lattice QCD
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• Electroproduction of the S11(1535) Resonance at High Momentum Transfer
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• Polarizability of the Nucleon and Compton Scattering
• Electromagnetic Form Factors of the Nucleon in an Improved Quark Model
• Measurement of the pi^+ meson polarizabilities via the gamma p->gamma pi^+ n reaction
• Measurement of the Rate of Muon Capture in Hydrogen Gas and Determination of the Proton's Pseudoscalar Coupling $g_P$
• $Q^2$ Independence of $Q{F}_2/F_1$, Poincare Invariance and the Non-Conservation of Helicity
• Structure analysis of the virtual Compton scattering amplitude at low energies
• The Strangeness Radius and Magnetic Moment of the Nucleon Revisited
• The Q^2 evolution of the generalized Gerasimov-Drell-Hearn integral for the neutron using a He-3 target
• Spin structure of the nucleon at low energies
• Aspects of Nucleon Compton Scattering
• Q^2 Evolution of the Neutron Spin Structure Moments using a He-3 Target
• Electroexcitation of the P33(1232), P11(1440), D13(1520), S11(1535) at Q^2=0.4 and 0.65(GeV/c)^2
• Measurement of the Proton Spin Structure Function $g_1(x,Q^2)$ for $Q^2$ from 0.15 to 1.6 GeV${}^2$ with CLAS
• SU(6) breaking effects in the nucleon elastic electromagnetic form factors
• Electromagnetic Nucleon-to-Delta Transition in Chiral Effective-Field Theory
• The nucleon's strange electromagnetic and scalar matrix elements
• Test of low-energy theorems for p(\vec{gamma},π^{0})p in the threshold region
• Fixed-t subtracted dispersion relations for Compton scattering off the nucleon
• A chiral bag model approach to delta electroproduction
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• On Nucleon Electromagnetic Form Factors
• The first determination of Generalized Polarizabilities of the proton by a Virtual Compton Scattering experiment
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• Nucleon Structure and Parity-Violating Electron Scattering
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• Pi0 photo- and electroproduction at threshold within a dynamical model
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• Parameterisation of σ_{1/2}-σ_{3/2} for Q^2 \geq 0 and non-resonance contribution to the GDH sum rule
• Measurement of the Sigma^- Charge Radius by Sigma^- Electron Elastic Scattering
• A measurement of the CP-conserving component of the decay KS -> pi+ pi- pi0
• Measurement of the cross section for e^+e^- -> ppbar at center-of-mass energies from 2.0 to 3.07 GeV
• High-Energy Forward Scattering and the Pomeron: Simple Pole versus Unitarized Models
• Dispersion relation formalism for virtual Compton scattering off the proton
• Lowest Q^2 Measurement of the gamma*p -> Delta Reaction: Probing the Pionic Contribution
• Chiral symmetry and the reaction $\gamma p\to {\pi }^{0}p$
• Leading and higher twists in the proton polarized structure function at large Bjorken x
• Compton scattering on the proton, neutron, and deuteron in chiral perturbation theory to O(Q^4)
• Generalized Polarizabilities and the Chiral Structure of the Nucleon
• Generalized Polarizabilities of the Nucleon in Chiral Effective Theories
• Deuteron Compton scattering below pion photoproduction threshold
• Virtual Compton Scattering off the Nucleon in Chiral Perturbation Theory
• Electroweak structure of the nucleon, meson cloud and light-cone wavefunctions
• Spin Asymmetry and Gerasimov-Drell-Hearn Sum Rule for the Deuteron
• Improved description of threshold pion electroproduction in chiral perturbation theory
• Electromagnetic form factors of the nucleon in the chiral quark soliton model
• Measurement of the Polarized Structure Function ${\sigma }_{L{T}^{\prime }}$ for $p(\vec{e},e^{\prime }{\pi }^{+})n$ in the $\Delta (1232)$ Resonance Region
• Signatures of chiral dynamics in the Nucleon to Delta transition
• Proton spin polarizabilities from polarized Compton scattering
• Measurement of the LT-asymmetry in π^0 electroproduction at the energy of the Δ(1232) resonance
• Strange form factors in the context of SAMPLE, HAPPEX, and A4 experiments
• Measurement of the Generalized Forward Spin Polarizabilities of the Neutron
• Novel analysis of chiral loop effects in the generalized Gerasimov-Drell-Hearn sum rule
• Determination of quadrupole strengths in the gamma*p-->Delta(1232) transition at Q2= 0.20 (GeV/c)2
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• The Gerasimov-Drell-Hearn Sum Rule and the Spin Structure of the Nucleon
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• Elastic Compton scattering from the deuteron and nucleon polarizabilities
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• Measurement of the Generalized Polarizabilities of the Proton in Virtual Compton Scattering at Q2= 0.92 and 1.76 GeV2
• The Nucleon Spin Polarizability at Order $\mathcal{O}(p^4$) in Chiral Perturbation Theory
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• The $Q^2$-dependence of the generalised Gerasimov-Drell-Hearn integral for the deuteron, proton and neutron
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• The shape of the nucleon
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• The Drell-Hearn Sum Rule at Order Alpha**3
• On Nucleon Electromagnetic Form Factors: A Pre'cis
• Sum rule for the backward spin polarizability of the nucleon from a backward dispersion relation
• Generalized polarizabilities of the nucleon studied in the linear sigma model (II)
• CLASSICAL PHOTOABSORPTION SUM RULES
• The Spin and Flavour Dependence of High-Energy Photoabsorption
• Quasi-free Compton Scattering from the Deuteron and Nucleon Polarizabilities
• Generalized polarizabilities of the proton in a constituent quark model revisited
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• $\pi$NN coupling and two-pion photoproduction on the nucleon
• The pion charge radius from charged pion electroproduction
• Electromagnetic polarizabilities and the excited states of the nucleon
• Nucleon Form Factors in Dispersion Theory
• What QCD Tells Us About Nature -- and Why We Should Listen
• Gravitons and the Drell-Hearn-Gerasimov Sum Rule
• Experiments with polarized 3He at MAMI

Cited by in corpus (29)

• Baryons as relativistic three-quark bound states
• Baryon spectroscopy
• Progress Toward Understanding Baryon Resonances
• Hadron structure from lattice quantum chromodynamics
• Meson dominance of hadron form factors and large-Nc phenomenology
• Model Analysis of the $ep\to e{p}^{\prime }{\pi }^{+}{\pi }^{-}$ Electroproduction Reaction on the Proton
• High-accuracy calculation of the deuteron charge and quadrupole form factors in chiral effective field theory
• Transition between nuclear and quark-gluon descriptions of hadrons and light nuclei
• Electromagnetic form factors of the nucleon in effective field theory
• Hadron Polarizabilities
• Nucleon Compton scattering in the Dyson-Schwinger approach
• Novel two-to-three hard hadronic processes and possible studies of generalized parton distributions at hadron facilities
• Higher order forward spin polarizability
• Unified description of hadron-photon and hadron-meson scattering in the Dyson-Schwinger approach
• Moments of Spin Structure Functions: Sum Rules and Polarizabilities
• Single pion contribution to the hyperfine splitting in muonic hydrogen
• Pion constituent quarks couplings strong form factors: a dynamical approach
• 70 Years of Hyperon Spectroscopy: A review of strange $\Xi$, $\Omega$ baryons, and the spectrum of charmed and bottom baryons
• Form factors for pions couplings to constituent quarks under weak magnetic field
• Delta resonances, quark models, chiral symmetry and AdS/QCD
• New approach to low energy Virtual Compton Scattering and generalized polarizabilities of the nucleon
• Nucleon Polarizabilities: Theory
• Constituent quark axial current couplings to light vector mesons in the vacuum and with a weak magnetic field
• Strongly interacting matter in extreme magnetic fields
• Hadron structure at small momentum transfer
• Chiral effective field theories of the strong interactions
• van der Waals and Casimir-Polder interactions between neutrons
• Measurement of the high-energy contribution to the Gerasimov-Drell-Hearn sum rule
• From QCD-Based Descriptions to Direct Fits: A Unified Study of Nucleon Electromagnetic Form Factors