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Интеллектуальная Система Тематического Исследования НАукометрических данных |
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Studies of nucleon resonance electrocouplings $\gamma_{v}NN^*$ from the data on exclusive meson electroproduction off nucleons represents an important part in the N$^*$ Program with the CLAS detector \cite{Bu11}, allowing us to explore the non-perturbative strong interaction that is responsible for the formation of the nucleon and its excited states.\cite{CL12}. The CLAS measurements have extended considerably the data base on differential cross sections for N$\pi$ and N$\eta$ electroproduction channels, longitudinally polarized beam and beam-target asymmetries for $\pi$ electroproduction off protons at $Q^2$ up to 6.0 GeV$^2$. Electrocouplings of the $P_{11}(1440)$, $D_{13}(1520)$, and $S_{11}(1535)$ resonances were determined in analyses within the framework of two conceptually different reaction models \cite{Az09}. Data were also collected on charged double pion electroproduction off protons leading to nine independent differential $\pi^{+}\pi^{-}p$ cross sections at $Q^2$ up to 1.5 GeV$^2$. Using a phenomenological approach \cite{Mo09}, the $P_{11}(1440)$ and $D_{13}(1520)$ electrocouplings were determined from the $\pi^+\pi^-p$ electroproduction data for the first time. The results are consistent with the results of the independent N$\pi$ electroproduction analyses \cite{Az09}. Electrocouplings of the $S_{31}(1620)$, $S_{11}(1650)$, $D_{33}(1700)$, and $P_{13}(1720)$ states have also become available from this channel \cite{Mo11}. These results revealed that there exist two major contributions to $\gamma_{v}NN^*$ electrocouplings: a) an internal quark core, and b) an external meson-baryon cloud. Recent theoretical developments using the Dyson-Schwinger Equations of QCD for the interpretations of $\gamma_{v}NN^*$ electrocouplings provide guidelines to search for the manifestation of dynamically dressed quark masses. Lattice QCD is making progress toward $\gamma_{v}NN^*$ electrocoupling description from QCD Lagrangian. The new data will be discussed in light of these new developments. A further extension of the N$^*$ Program with the CLAS12 detector after completion of JLAB 12 GeV Upgrade Project will be presented. \begin{thebibliography}{99} \bibitem{Bu11} I~.G.~Aznauryan and V.~D.~Burkert, Prog. Part. Phys.,1 (2012). \bibitem{CL12} I.~G.~Aznauryan, et al., arXiv:0907.1901 [nucl-th]. \bibitem{Az09} I.~G.Aznauryan, et al., Phys. Rev. {\bf C80}, 055203 (2009). \bibitem{Mo09} V.I.Mokeev, et al., Phys. Rev. {\bf C80}, 045212 (2009). \bibitem{Mo11} I.G.Aznauryan, V.D.Burkert, and V.I.Mokeev, arXiv:1108.1125