Measurement of $ep \to e^{'}p\pi^{+}\pi^{-}$: experimental procedures and baryon resonance analysis

TL;DR

This paper reports on the measurement of the $ep o e'p\, ext{π}^+ ext{π}^-$ reaction cross section in the resonance region, revealing new structures and discrepancies with existing models, suggesting possible new baryon states or resonance property changes.

Contribution

It provides new experimental data on baryon resonance structures and highlights the need to revise existing models or consider new baryon states.

Findings

Resonant structures not seen in previous experiments

Discrepancies with phenomenological predictions

Possible indication of a new baryon state or altered resonance properties

Abstract

The cross section for the reaction $ e p \to e^{\prime} p \pi^{+} \pi^{-}$ was measured in the resonance region for 1.4$<$W$<$2.1 GeV and 0.5$<Q^{2}<$1.5 GeV$^{2}$/c$^{2}$ using the CLAS detector at Jefferson Laboratory. The data show resonant structures not visible in previous experiments. The comparison of our data to a phenomenological prediction using available information on $N^{*}$ and $\Delta$ states shows an evident discrepancy. A better description of the data is obtained either by a sizeable change of the properties of the $P_{13}$(1720) resonance or by introducing a new baryon state, not reported in published analyses.