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

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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.