Study of the $pp \to np\pi^+$ reaction at 1.25 GeV with HADES

Abstract

In pp collisions at 1.25 GeV kinetic energy, the HADES collaboration aimed at investigating the di-electron production related to $\Delta$ (1232) Dalitz decay ($\Delta^+ \to pe^+e^-$). In order to constrain the models predicting the cross section and the production mechanisms of $\Delta$ resonance, the hadronic channels have been measured and studied in parallel to the leptonic channels. The analyses of $pp\to np\pi^+$ and $pp\to pp\pi^0$ channels and the comparison to simulations are presented in this contribution, in particular the angular distributions being sensitive to $\Delta$ production and decay. The accurate acceptance corrections have been performed as well, which could be tested in all the phase space region thanks to the high statistic data. These analyses result in an overall agreement with the one-$\pi$ exchange model and previous data.