Two Pion Photo- and Electroproduction with CLAS

TL;DR

This paper presents extensive CLAS data on pion photo- and electroproduction, revealing new insights into nucleon resonance spectrum, electrocouplings, and decay channels, advancing understanding of strong QCD.

Contribution

It provides the first electrocouplings of specific nucleon excited states from $ ext{π}^+ ext{π}^- ext{p}$ data at higher photon virtualities, and evidence for a new candidate resonance.

Findings

Electrocouplings of $N(1440)1/2^+$ and $N(1520)3/2^-$ determined at $Q^2$ 2-5 GeV$^2$

Improved knowledge of nucleon resonance photocouplings in 1.6-2.0 GeV mass range

Evidence for the candidate-state $N'(1720)3/2^+$

Abstract

Exclusive $\pi^+\pi^-p$ photo- and electroproduction data from CLAS have considerably extended the information on the spectrum and structure of nucleon resonances. The data from the $\pi^+\pi^-p$ and $N\pi$ 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 $\pi^+\pi^-p$ 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 $\pi \Delta$ and $\rho p$ 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 $\pi^+\pi^-p$ data at 2.0 GeV$^2$ $<$ $Q^2$ $<$ 5.0 GeV$^2$. Analyses of the combined $\pi^+\pi^-p$ 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 $\pi^+\pi^-p$ photo- and electroproduction data, and their impact on the exploration of strong QCD are presented.