Evidence for the $N^{\prime }(1720)3/2^{+}$ Nucleon Resonance from Combined Studies of CLAS ${\pi }^{+}{\pi }^{-}p$ Photo- and Electroproduction Data

Abstract

The analysis of the nine 1-fold differential cross sections for the ${\gamma }_{r,v}p\to {\pi }^{+}{\pi }^{-}p$ photo- and electroproduction reactions obtained with the CLAS detector at Jefferson Laboratory was carried out with the goal to establish the contributing resonances in the mass range from 1.6~GeV to 1.8~GeV. In order to describe the photo- and electroproduction data with $Q^2$-independent resonance masses and hadronic decay widths in the $Q^2$ range below 1.5~GeV${}^2$, it was found that an $N^{\prime }(1720)3/2^{+}$ state is required in addition to the already well-established nucleon resonances. This work demonstrates that the combined studies of ${\pi }^{+}{\pi }^{-}p$ photo- and electroproduction data are vital for the observation of this resonance. The contributions from the $N^{\prime }(1720)3/2^{+}$ state and the already established $N(1720)3/2^{+}$ state with a mass of 1.745~GeV are well separated by their different hadronic decays to the $\pi \Delta$ and $\rho p$ final states and the different $Q^2$-evolution of their photo-/electroexcitation amplitudes. The $N^{\prime }(1720)3/2^{+}$ state is the first recently established baryon resonance for which the results on the $Q^2$-evolution of the photo-/electrocouplings have become available. These results are important for the exploration of the nature of the ``missing'' baryon resonances.

accepted for publication in Phys. Lett. B

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