Dilepton production in pp and np collisions at 1.25 GeV

Abstract

The inclusive reactions $pp\to e^{+}{e}^{-}X$ and $np\to e^{+}{e}^{-}X$ at the laboratory kinetic energy of 1.25 GeV are investigated in a model of dominance of nucleon and $\Delta$ resonances. Experimental data for these reactions have recently been reported by the HADES Collaboration. In the original model, the dileptons are produced either from the decays of nucleon and $\Delta$ resonances $R\to N{e}^{+}{e}^{-}$ or from the Dalitz decays of ${\pi }^0$- and $\eta$-mesons created in the $R\to N{\pi }^0$ and $R\to N\eta$ decays. We found that the distribution of dilepton invariant masses in the $pp\to e^{+}{e}^{-}X$ reaction is well reproduced by the contributions of $R\to N{e}^{+}{e}^{-}$ decays and $R\to N{\pi }^0$, ${\pi }^0\to \gamma e^{+}{e}^{-}$ decays. Among the resonances, the predominant contribution comes from the $\Delta (1232)$, which determines both the direct decay channel $R\to N{e}^{+}{e}^{-}$ and the pion decay channel. In the collisions $np\to e^{+}{e}^{-}X$, additional significant contributions arise from the $\eta$-meson Dalitz decays, produced in the $np\to np\eta$ and $np\to d\eta$ reactions, the radiative capture $np\to d{e}^{+}{e}^{-}$, and the $np\to np{e}^{+}{e}^{-}$ bremsstrahlung. These mechanisms may partly explain the strong excess of dileptons in the cross section for collisions of $np$ versus $pp$, which ranges from 7 to 100 times for the dilepton invariant masses of 0.2 to 0.5 GeV.

References in corpus (4)

• ABC Effect in Basic Double-Pionic Fusion --- Observation of a new resonance?
• Origin of the low-mass electron pair excess in light nucleus-nucleus collisions
• Dilepton production in proton-proton and quasifree proton-neutron reactions at 1.25 GeV
• Dilepton production in nucleon-nucleon collisions reexamined

Cited by in corpus (5)

• Measurement of the $pn\to pp{\pi }^0{\pi }^{-}$ Reaction in Search for the Recently Observed Resonance Structure in $d{\pi }^0{\pi }^0$ and $d{\pi }^{+}{\pi }^{-}$ systems
• Dilepton production in proton-induced reactions at SIS energies with the GiBUU transport model
• Dilepton production and resonance properties within a new hadronic transport approach in the context of the GSI-HADES experimental data
• On a Possible Explanation of the DLS-Puzzle
• Analysis of the exclusive final state npe${}^{+}$e${}^{-}$ in quasi-free np reaction