$\gamma_{v}NN^*$ Transition Amplitudes and Excited Baryon Structure from CLAS

Studying excited nucleon structure through exclusive-meson electroproduction reactions is key for understanding the nature of the strong interaction in the non-perturbative regime. With its nearly complete coverage of the final-state phase space, the CLAS detector at JLab has provided the lion's share of the world's meson-electroproduction data for differential cross sections and the asymmetries arising from single- and double-polarization observables. Electrocouplings for most of the excited nucleon states ($N^*$) in mass range of up to 1.8~GeV have been determined from several analyses of the CLAS data for photon virtualities ($Q^2$) up to 5.0 GeV$^2$ for the $\pi^+n$, $\pi^0p$, and $\eta p$ channels [1,3] as well as for the $\pi^+\pi^-p$ reaction for $Q^2 < 1.5$~GeV$^2$ [2,3]. Physics analyses of these $N^*$ electrocouplings [2,3] have revealed that the structure of excited nucleon is formed of an internal core of dressed quarks with an external meson-baryon cloud. Our $N^*$-electrocoupling results afford access to the non-perturbative strong interaction responsible for generating the different $N^*$ states and will also provide testing ground for the inspired by QCD quark model predictions. A dedicated experiment will run after the 12 GeV upgrade to JLab on the extraction of the $N^*$ electrocouplings in the yet unexplored region of high photon virtualities ranging from 5.0 to 12 GeV$^2$. The anticipated results are of particular importance in providing a understanding of the nature of confinement and dynamical chiral symmetry breaking in baryons based upon the QCD [3].\\[4pt] [1] I.G. Aznauryan and V.D. Burkert, Prog. Part. Nucl. Phys. \textbf{67}, 1 (2012).\\[0pt] [2] V.I. Mokeev \textit{et~al.} (CLAS Collaboration), Phys. Rev. \textbf{C86}, 035203 (2012).\\[0pt] [3] I.G. Aznauryan \textit{et~al.}, ``Studies of Nucleon Resonance Structure in Exclusive Meson Electroproduction,'' arXiv:1212.4891[nucl-th].