Measurement of single- and double-polarization observables in the photoproduction of ${\pi }^{+}{\pi }^{-}$~meson pairs off the proton using CLAS at Jefferson Laboratory

The photoproduction of ${\pi }^{+}{\pi }^{-}$ meson pairs off the proton has been studied in the reaction $\gamma p\to p{\pi }^{+}{\pi }^{-}$ using the CEBAF Large Acceptance Spectrometer (CLAS) and the frozen-spin target (FROST) in Hall B at the Thomas Jefferson National Accelerator Facility. For the first time, the beam and target asymmetries, $I^{s,c}$ and $P_{x,y}$, have been measured along with the beam-target double-polarization observables, $P_{x,y}^{s,c}$, using a transversely polarized target with center-of-mass energies ranging from 1.51 GeV up to 2.04 GeV. These data and additional $\pi \pi$ photoproduction observables from CLAS and experiments elsewhere were included in a partial-wave analysis within the Bonn-Gatchina framework. Significant contributions from $s$-channel resonance production are observed in addition to $t$-channel exchange processes. The data indicate significant contributions from $N^{\ast }$ and ${\mathrm{\Delta }}^{\ast }$ resonances in the third and fourth resonance regions.