Abstract
In this paper we report on the investigation of baryonic resonance production in proton-proton collisions at the kinetic energies of 1.25 GeV and 3.5 GeV, based on data measured with HADES. Exclusive channels npπ+ and ppπ0 as well as ppe+e- were studied simultaneously in the framework of a one-boson exchange model. The resonance cross sections were determined from the one-pion channels for Δ(1232) and N(1440) (1.25 GeV) as well as further Δ and N∗ resonances up to 2 GeV/c2 for the 3.5 GeV data. The data at 1.25 GeV energy were also analysed within the framework of the partial wave analysis together with the set of several other measurements at lower energies. The obtained solutions provided the evolution of resonance production with the beam energy, showing a sizeable non-resonant contribution but with still dominating contribution of Δ(1232)P33. In the case of 3.5 GeV data, the study of the ppe+e- channel gave the insight on the Dalitz decays of the baryon resonances and, in particular, on the electromagnetic transition form-factors in the time-like region. We show that the assumption of a constant electromagnetic transition form-factors leads to underestimation of the yield in the dielectron invariant mass spectrum below the vector mesons pole. On the other hand, a comparison with various transport models shows the important role of intermediate ρ production, though with a large model dependency. The exclusive channels analysis done by the HADES collaboration provides new stringent restrictions on the parameterizations used in the models.
Highlights
A path to understanding nuclear forces usually begins with the studies of nucleon-nucleon reactions
Over the years various approaches were studied within the one-boson exchange (OBE) model successfully describing the data
The analysis of one-pion production channels in reactions pp → ppπ0 and pp → npπ+ leads to a good description of various differential distributions, yet the total cross sections predicted by the model are lower than the reconstructed from the experimental data
Summary
A path to understanding nuclear forces usually begins with the studies of nucleon-nucleon reactions. The analysis of one-pion production channels in reactions pp → ppπ0 and pp → npπ+ (see [9,10,11,12]) leads to a good description of various differential distributions, yet the total cross sections predicted by the model are lower than the reconstructed from the experimental data Another model describing the data in the npπ+ channel in the quite wide energy range 0.97 − 4.0 GeV (see [13,14,15]), introduced by Dmitriev, Sushkov and Gaarde [16], had essentially similar assumptions of one-pion exchange but different vertex parameterization. In this work we discuss the results from the exclusive hadronic channels pp → npπ+, pp → ppπ0 investigated at the kinetic beam energies of 1.25 and 3.5 GeV and a dilepton channel pp → ppe+e− investigated at the kinetic beam energy of 3.5 GeV
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