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Study of baryonic resonances in the channel pp->ppπ⁺π⁻ at 3.5 GeV beam energy with the HADES detector

Abstract : The subject of this thesis is the analysis of the pp->ppπ⁺π⁻ reaction measured at a beam energy of 3.5 GeV with the High Acceptance Di-Electron Spectrometer (HADES) at GSI. The aim is to provide additional information on the production of a pion and a kaon measured by HADES for the excitation of a resonance as well as new results for the production of two resonances and the ρ meson production. Such information is important, in particular, for the interpretation of the di-electron spectra measured by the HADES collaboration. The extraction of the signal for pp->ppπ⁺π⁻ production is based on the detection of one proton, one π⁺ and one π⁻ in the HADES detector and the calculation of the missing mass. Statistical errors are negligible and systematic errors are mainly due to the efficiency corrections which are based on simulations and to normalization. A simple model based on PLUTO event generator was built for the interpretation of the data, by including three main types of contributions: the production of one resonance decaying into pπ⁺π⁻ and the excitation of two resonances, decaying respectively into pπ⁺ and pπ⁻ and the direct ρ production. A fitting procedure is developed, using as constraint the information obtained for the single resonance excitation from one pion and one kaon production data. The contribution of the ρ meson was also extracted after applying necessary kinematical cuts. Among all the identified contributions, the main ones are the double Δ(1232) excitation and the N(1520) excitation. A Lagrangian model was developed for these two contributions, the calculations give a similar result to the simple model and predict a negligible interferences effect. Finally, the confrontation of the experimental results to the predictions of existing theoretical models shows the necessity to take into account these new data for the description of mesons and di-electron production in nuclear collisions above 1.5 GeV/nucleus.
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Submitted on : Wednesday, May 20, 2020 - 5:04:09 PM
Last modification on : Friday, May 29, 2020 - 4:01:59 AM

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  • HAL Id : tel-02614181, version 1

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Amel Belounnas. Study of baryonic resonances in the channel pp->ppπ⁺π⁻ at 3.5 GeV beam energy with the HADES detector. Nuclear Experiment [nucl-ex]. Université Paris-Saclay, 2019. English. ⟨NNT : 2019SACLS243⟩. ⟨tel-02614181⟩

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