First results on nucleon resonance electroexcitation amplitudes from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>e</mml:mi><mml:mi>p</mml:mi><mml:mo>→</mml:mo><mml:msup><mml:mi>e</mml:mi><mml:mo>′</mml:mo></mml:msup><mml:msup><mml:mi>π</mml:mi><mml:mo>+</mml:mo></mml:msup><mml:msup><mml:mi>π</mml:mi><mml:mo>−</mml:mo></mml:msup><mml:msup><mml:mi>p</mml:mi><mml:mo>′</mml:mo></mml:msup></mml:mrow></mml:math> cross sections at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>W</mml:mi><mml:mo>=</mml:mo><mml:mn>1.4</mml:mn><mml:mtext>–</mml:mtext><mml:mn>1.7</mml:mn></mml:mrow></mml:math> GeV and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mi>Q</mml:mi><mml:mn>2</mml:mn></mml:msup><mml:mo>=</mml:mo><mml:mn>2.0</mml:mn><mml:mtext>–</mml:mtext><mml:mn>5.0</mml:mn><mml:mspace width="0.16em"/><mml:msup><mml:mrow><mml:mi>GeV</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msup></mml:mrow></mml:math>

Abstract

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.

Topics & Concepts