Electroexcitation of the Roper resonance for1.7<Q2<4.5GeV2ine→p→enπ+

The helicity amplitudes of the electroexcitation of the Roper resonance are extracted for $1.7l{Q}^{2}l4.5\phantom{\rule{0.3em}{0ex}}{\mathrm{GeV}}^{2}$ from recent high precision JLab-CLAS cross section and longitudinally polarized beam asymmetry data for ${\ensuremath{\pi}}^{+}$ electroproduction on protons at $W=1.15\ensuremath{-}1.69$ GeV. The analysis is made using two approaches, dispersion relations and a unitary isobar model, which give consistent ${Q}^{2}$ behavior of the helicity amplitudes for the ${\ensuremath{\gamma}}^{*}p\ensuremath{\rightarrow}$N(1440)P${}_{11}$ transition. It is found that the transverse helicity amplitude ${A}_{1/2}$, which is large and negative at ${Q}^{2}=0$, becomes large and positive at ${Q}^{2}\ensuremath{\simeq}2\phantom{\rule{0.3em}{0ex}}{\mathrm{GeV}}^{2}$, and then drops slowly with ${Q}^{2}$. The longitudinal helicity amplitude ${S}_{1/2}$, which was previously found from CLAS $\stackrel{\ensuremath{\rightarrow}}{e}p\ensuremath{\rightarrow}\mathit{ep}{\ensuremath{\pi}}^{0},\mathit{en}{\ensuremath{\pi}}^{+}$ data to be large and positive at ${Q}^{2}=0.4,0.65\phantom{\rule{0.3em}{0ex}}{\mathrm{GeV}}^{2}$, drops with ${Q}^{2}$. Available model predictions for ${\ensuremath{\gamma}}^{*}p\ensuremath{\rightarrow}$N(1440)P${}_{11}$ allow us to conclude that these results provide strong evidence in favor of N(1440)P${}_{11}$ as a first radial excitation of the $3q$ ground state. The results of the present paper also confirm the conclusion of our previous analysis for ${Q}^{2}l1$ GeV${}^{2}$ that the presentation of N(1440)P${}_{11}$ as a q$^{3}\mathrm{G}$ hybrid state is ruled out.