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- Doctoral Thesis (1) (remove)
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The production of _j63 [eta] and _w63 [omega] mesons in 3.5 GeV p+p interaction in HADES
(2011)
- The study of meson production in proton-proton collisions in the energy range up to one GeV above the production threshold provides valuable information about the nature of the nucleon-nucleon interaction. Theoretical models describe the interaction between nucleons via the exchange of mesons. In such models, different mechanisms contribute to the production of the mesons in nucleon-nucleon collisions. The measurement of total and differential production cross sections provide information which can help in determining the magnitude of the various mechanisms. Moreover, such cross section information serves as an input to the transport calculations which describe e.g. the production of e+e− pairs in proton- and pion-induced reactions as well as in heavy ion collisions. In this thesis, the production of ω and η mesons in proton-proton collisions at 3.5 GeV beam energy was studied using the High Acceptance DiElectron Spectrometer (HADES) installed at the Schwerionensynchrotron (SIS 18) at the Helmholtzzenturm f¨ur Schwerionenforschung in Darmstadt. About 80 000 ω mesons and 35 000 η mesons were reconstructed. Total production cross sections of both mesons were determined. Furthermore, the collected statistics allowed for extracting angular distributions of both mesons as well as performing Dalitz plot studies. The ω and η mesons were reconstructed via their decay into three pions (π+π−π0) in the exclusive reaction pp −→ ppπ+π−π0. The charged particles were identified via their characteristic energy loss, via the measurement of their time of flight and momentum, or using kinematics. The neutral pion was reconstructed using the missing mass method. A kinematic fit was applied to improve the resolution and to select events in which a π0 was produced. The correction of measured yields for the effects of spectrometer acceptance was done as a function of four variables (two invariant masses and two angles). Systematic studies of the acceptance for different input distributions were performed. The measured yields were normalized to the number of measured events of elastic scattering. Systematic errors due to the methods of the data analysis and the background subtraction were investigated. Production angular distributions of ω and η mesons were measured. Both mesons exhibit a slightly anisotropic angular distribution. The Dalitz plot of ω meson production shows indications of resonant production. However, the deviation of the distribution from the one expected by phase space simulations is not large. The Dalitz plot of η meson production shows a signal of the production via the N(1535) resonance, The contribution of N(1535) to the production was quantified to be about 47%. The angular distribution of η mesons does not show significant differences between resonant and non resonant production. The total production cross section of ω mesons in the reaction pp −→ ppω was determined to be 106.5 ± 0.9 (stat) ± 7.9 (sys) [μb] where stat indicates statistical error and sys indicates systematic error, while that of η mesons was determined to be 136.9 ± 0.9 (stat) ± 10.1 (sys) [μb] in the reaction pp −→ ppη
