Two Pion Photo- and Electroproduction with CLAS

Abstract

Exclusive $π^+π^-p$ photo- and electroproduction data from CLAS have considerably extended the information on the spectrum and structure of nucleon resonances. The data from the $π^+π^-p$ and $Nπ$ channels have provided results on the electrocouplings of most resonances in the mass region up to 1.8 GeV and at photon virtualities up to 5.0 GeV$^2$. The recent CLAS data on $π^+π^-p$ photoproduction have improved knowledge on the photocouplings of nucleon resonances in the mass range of 1.6 GeV $<$ $M_{N^*}$ $<$ 2.0 GeV and on their decays to the $πΔ$ and $ρp$ final hadron states. For the first time, the electrocouplings of the $N(1440)1/2^+$ and $N(1520)3/2^-$ excited states have become available from $π^+π^-p$ data at 2.0 GeV$^2$ $<$ $Q^2$ $<$ 5.0 GeV$^2$. Analyses of the combined $π^+π^-p$ photo- and electroproduction data have revealed evidence for the candidate-state $N'(1720)3/2^+$. The new results on the nucleon resonance spectrum, electroexcitation amplitudes from analysis of the CLAS $π^+π^-p$ photo- and electroproduction data, and their impact on the exploration of strong QCD are presented.