We report on the investigation of $\mathrm{\Delta }$(1232) production and decay in proton-proton collisions at a kinetic energy of 1.25 GeV measured with HADES. Exclusive dilepton decay channels $pp{e}^{+}{e}^{-}$ and $pp{e}^{+}{e}^{-}\gamma$ have been studied and compared with the partial-wave analysis of the hadronic $pp{\pi }^0$ channel. They allow to access both ${\mathrm{\Delta }}^{+}\to p{\pi }^0\left(e^{+}{e}^{-}\gamma \right)$ and ${\mathrm{\Delta }}^{+}\to p{e}^{+}{e}^{-}$ Dalitz decay channels. The perfect reconstruction of the well-known ${\pi }^0$ Dalitz decay serves as a proof of the consistency of the analysis. The $\mathrm{\Delta }$ Dalitz decay is identified for the first time and the sensitivity to $N-\mathrm{\Delta }$ transition form factors is tested. The $\mathrm{\Delta }$(1232) Dalitz decay branching ratio is also determined for the first time; our result is (4.19 $\pm$ 0.62 syst. $\pm$ 0.34 stat.) $\times {10}^{-5}$, albeit with some model dependence.

• Received 24 March 2017

DOI:https://doi.org/10.1103/PhysRevC.95.065205