Strong QCD Insights from Excited Nucleon Structure Studies with CLAS and CLAS12

Abstract

Studies of the spectrum of hadrons and their structure in experiments with electromagnetic probes offer unique insight into many facets of the strong interaction in the regime of large quark-gluon running coupling, {\it i.e.} the regime of strong QCD. The experimental program within Hall~B at Jefferson Laboratory based on data acquired with the CLAS spectrometer using electron and photon beams with energies up to 6~GeV has already considerably extended the scope of research in hadron physics in joint efforts between experiment and phenomenological data analysis. Impressive progress in relating the hadron structure observables inferred from the data to the strong QCD mechanisms underlying hadron mass generation has been achieved in the past decade. These results will be considerably extended with data from the experimental program with the new CLAS12 spectrometer that has begun data taking using electron beams with energies up to 11~GeV. With this extended kinematic reach the structure of nucleon resonances will be probed at the highest photon virtualities ever achieved in the studies of exclusive electroproduction, which will allow for the exploration of the distance scale where $>$98\% of light hadron mass emerges from QCD in the transition of the strong interaction from the regime of quark-gluon confinement to perturbative QCD.

24 pages, 12 figures, review paper for topical FBS issue

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• Dressed-quark anomalous magnetic moments
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• Neutral Pion Electroproduction in the Resonance Region at High $Q^2$
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• Emergence of pion parton distributions
• Jülich-Bonn-Washington Model for Pion Electroproduction Multipoles
• Parton distributions of light quarks and antiquarks in the proton
• Dynamical diquarks in the ${\mathbf{\gamma }}^{(\ast )}\mathbf{p}\to \mathbf{N}(1535){\frac{1}{2}}^{-}$ transition
• Photo- and Electrocouplings of Nucleon Resonances
• Schwinger mechanism for gluons from lattice QCD
• Coupled-channel analysis of pion- and eta-electroproduction with the Jülich-Bonn-Washington model
• Nucleon axial form factor at large momentum transfers
• Resonant contributions to inclusive nucleon structure functions from exclusive meson electroproduction data
• Origin of the Proton Mass
• Composition of low-lying $\mathbf{J}={\frac{3}{2}}^{\pm }\mathbf{\Delta }$-baryons
• Beam-Recoil Transferred Polarization in $K^{+}Y$ Electroproduction in the Nucleon Resonance Region with CLAS12
• $\Lambda$ and $\Sigma$ Excitations and the Quark Model
• Resonant contributions to polarized proton structure functions
• $\Delta$-baryon axialvector and pseudoscalar form factors, and associated PCAC relations
• Global Data-Driven Determination of Baryon Transition Form Factors
• Symplectic Effective Field Theory for Nuclear Structure Studies
• Polarized proton structure in the resonance region