First results on nucleon resonance electroexcitation amplitudes from ep→e′π+π−p′ cross sections at

V. Mokeev, P. Achenbach,Volker Burkert, D. S. Carman, R. W. Gothe, A. N. Hiller Blin, E. L. Isupov, K. S. Joo, K. Neupane, A. Trivedi

The electroexcitation amplitudes or ${\ensuremath{\gamma}}_{v}p{N}^{*}$ electrocouplings of the $N(1440)1/{2}^{+}$, $N(1520)3/{2}^{\ensuremath{-}}$, and $\mathrm{\ensuremath{\Delta}}(1600)3/{2}^{+}$ resonances were obtained for the first time from the $ep\ensuremath{\rightarrow}{e}^{\ensuremath{'}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{p}^{\ensuremath{'}}$ differential cross sections measured with the CLAS detector at Jefferson Lab within the range of invariant mass $W=1.4\text{--}1.7$ GeV of the final state hadrons, for photon virtualities ${Q}^{2}=2.0\text{--}5.0$ ${\mathrm{GeV}}^{2}$. A good description of the nine independent onefold differential ${\ensuremath{\gamma}}_{v}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{p}^{\ensuremath{'}}$ cross sections achieved within the data-driven Jefferson Lab-Moscow State University (JM) meson-baryon reaction model in each bin of ($W,{Q}^{2}$) allows for separation of the resonant and nonresonant contributions. The electrocouplings were determined in the fits of the ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}p$ cross sections within three overlapping $W$ intervals with a substantial contribution from each of the three resonances listed above. Consistent results on the electrocouplings extracted from the data in these $W$ intervals provide evidence for their reliable extraction. These studies extend information on the electrocouplings of the $N(1440)1/{2}^{+}$ and $N(1520)3/{2}^{\ensuremath{-}}$ available from this channel over a broader range of ${Q}^{2}$. The electrocouplings of the $\mathrm{\ensuremath{\Delta}}(1600)3/{2}^{+}$, which decays preferentially into $\ensuremath{\pi}\ensuremath{\pi}N$ final states, have been determined for the first time. The reliable extraction of the electrocouplings for these states is also supported by the description of the ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}p$ differential cross sections with ${Q}^{2}$-independent masses and total/partial hadronic decay widths into the $\ensuremath{\pi}\mathrm{\ensuremath{\Delta}}$ and $\ensuremath{\rho}p$ final states.