The analysis of the nine 1-fold differential cross sections for the
γr,vp→π+π−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 Q2-independent resonance masses and hadronic decay widths in the Q2
range below 1.5~GeV2, it was found that an N′(1720)3/2+ state is required
in addition to the already well-established nucleon resonances. This work
demonstrates that the combined studies of π+π−p photo- and
electroproduction data are vital for the observation of this resonance. The
contributions from the N′(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 πΔ and ρp final states and the
different Q2-evolution of their photo-/electroexcitation amplitudes. The
N′(1720)3/2+ state is the first recently established baryon resonance for
which the results on the Q2-evolution of the photo-/electrocouplings have
become available. These results are important for the exploration of the nature
of the ``missing'' baryon resonances.Comment: accepted for publication in Phys. Lett.