$��$(1232) Dalitz decay in proton-proton collisions at T=1.25 GeV measured with HADES

We report on the investigation of $��$(1232) production and decay in proton-proton collisions at a kinetic energy of 1.25 GeV measured with HADES. Exclusive dilepton decay channels $ppe^{+}e^{-}$ and $ppe^{+}e^{-}��$ have been studied and compared with the partial wave analysis of the hadronic $pp��^{0}$ channel. They allow to access both $��^+ \to p��^0(e^+e^-��)$ and $��^+ \to pe^+e^-$ Dalitz decay channels. The perfect reconstruction of the well known $��^0$ Dalitz decay serves as a proof of the consistency of the analysis. The $��$ Dalitz decay is identified for the first time and the sensitivity to N-$��$ transition form factors is tested. The $��$(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.
13 pages, 7 figures