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

Abstract

We report on the investigation of $\Delta$(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 ${\Delta }^{+}\to p{\pi }^0(e^{+}{e}^{-}\gamma )$ and ${\Delta }^{+}\to p{e}^{+}{e}^{-}$ 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 $\Delta$ Dalitz decay is identified for the first time and the sensitivity to N-$\Delta$ transition form factors is tested. The $\Delta$(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.

13 pages, 7 figures

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• Two-Pion production in the second resonance region in ${\pi }^{-}p$ collisions with HADES
• Covariant model for the Dalitz decay of the $N(1535)$ resonance
• Analysis of the exclusive final state npe${}^{+}$e${}^{-}$ in quasi-free np reaction
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• ${\Sigma }^0$ production in proton nucleus collisions near threshold
• Correlated pion-proton pair emission off hot and dense QCD matter
• Meson cloud contributions to the Dalitz decays of decuplet to octet baryons
• Quark model calculations of transition form factors at high photon virtualities