Charge-exchange photoproduction of the $a_2^{-}\mathrm{}\left(1320\right)\mathrm{}$ in association with ${\Delta }^{++}$ at 19.3 GeV/c

We examine the negative $3\pi$ final state produced in association with ${\Delta }^{++}\mathrm{}\left(1232\right)\mathrm{}$ in the reaction $\gamma p\to {\Delta }^{++}{\pi }^{+}{\pi }^{-}{\pi }^{-}$ at an incident photon energy of 19.3 GeV. The most prominent enhancement in the $3\pi$ spectrum occurs at a mass and with a width consistent with the parameters of the $a_2\mathrm{}\left(1320\right)\mathrm{}$. This identification is confirmed by the various angular distributions. The $a_2$ production cross section, corrected for efficiencies and alternate $a_2$ decay modes, is 0.45±0.05 μb.