In einer systematischen Analyse wird die Produktion von ω-Mesonen in Proton-Proton-Kollisionen pp → ppω untersucht. Die Messung der experimentellen Daten wurde mit dem Flugzeitspektrometer COSY-TOF am Forschungszentrum Jülich für vier verschiedene Überschussenergien (ε = 92, 128, 129 und 173 MeV, ε = √s − 2 · mp − mω) durchgeführt. In der Analyse werden Ereignisse, in denen das kurzlebige ω-Meson über den Hauptzerfallskanal ω → π+π−π0 in drei Pionen zerfällt, gegenüber denen anderer Reaktionskanäle angereichert. Die Reaktion pp → ppω wird anschließend anhand der Signale in den Spektren der Missing Mass, das ist die im Ausgangskanal neben der invarianten Masse des Proton-Proton-Systems fehlenden Masse, untersucht. Totale sowie differentielle Wirkungsquerschnitte werden in verschiedenen Bezugssystemen bestimmt, u. a. die Winkelverteilungen der Protonen und ω-Mesonen im Schwerpunktsystem, Verteilungen von Jackson- und Helizitätswinkeln sowie die Spektren der invarianten Massen. Darüber hinaus wird mit Hilfe der Bestimmung der Zerfallsebenen der ω-Mesonen die Polarisation der ω-Mesonen ermittelt. Im Dreiteilchenausgangszustand ppω werden Bahndrehimpulse l > 0 nur für die ω-Mesonen gefunden. Aus der Messung folgt, dass bei ε = 92, 128 und 129 MeV maßgeblich Endzustände mit Bahndrehimpulsen lω = 0 ħ und lω = 1 ħ sowie bei ε = 173 MeV zusätzlich solche mit lω = 2 ħ zum Reaktionsprozess beitragen. Weitere Informationen über die beteiligten Partialwellen werden aus der Messung der Polarisation der ω-Mesonen gewonnen. Direkte Hinweise auf Beiträge von Nukleonresonanzen zum Produktionsprozess werden in keiner der untersuchten Observablen gefunden. Ein Szenario, in dem ω-Mesonen ausschließlich über Nukleonresonanzen produziert werden, kann anhand der Winkelverteilungen von Protonen und ω-Mesonen ausgeschlossen werden. / A systematic analysis of the production of ω mesons in proton-proton collisions pp → ppω is carried out. The experimental data were taken at Forschungszentrum Jülich with the COSY-TOF spectrometer at four different excess energies (ε = 92, 128, 129 and 173 MeV, ε = √s − 2 · mp − mω). In the analysis events with ω-mesons decaying via the main decay channel ω → π+π−π0 are enriched in relation to other reaction channels. Afterwards, the reaction pp → ppω is analysed based on the ω-signals in the spectra of the missing mass, i. e. the mass missing in the exit channel beside the proton-proton system. Total as well as differential cross sections are determined in different reference systems (angular distributions of ω-mesons and protons in CMS, distributions of Jackson and helicity angles, and invariant mass spectra). In addition the polarisation of the ω-mesons is determined. In the three particle exit channel ppω angular momenta l > 0 are seen only for ω-mesons. It is found that final states with angular momenta lω = 0 ħ and lω = 1 ħ contribute at excess energies ε = 92, 128 and 129 MeV. In addition states with lω = 2 ħ are seen at ε = 173MeV. Further informations on partial waves follows for the polarisation of the ω-meson. No observable shows direct signs of resonant contributions to the production process. In contrast, using the informations from the angular distributions of ω-mesons and protons a scenario with the exclusive production of ω-mesons through N* resonances can be excluded.

Universiẗat, Diss., 1997--Gießen.

University, Diss., 2005--Heidelberg.

No description available.

This Thesis presents measurements of the decays \Bm\to\Xi_c^0\bar{\Lambda}_c^-, \Bzb\to\Xi_c^+\bar{\Lambda}_c^- , \Bm\to\Lambda_c^+\bar{\Lambda}_c^-\Km, and \Bzb\to\Lambda_c^+\bar{\Lambda}_c^-\Kzb based on 228 million \upsbb decays collected with the \babar\ detector at the SLAC \pep2\ asymmetric-energy \B factory. The branching fraction of \Bm\to\Lambda_c^+\bar{\Lambda}_c^-\Km is measured to be $(1.22\pm0.16\pm 0.14\pm0.63)\times 10^{-3}$, and the branching fraction of $\Bz\to\Lambda_c^+\bar{\Lambda_c^-\Kzb$ is $(0.40\pm 0.33\pm 0.05 \pm 0.21)\times 10^{-3}$. The product $\BR(\Bm\to\Xi_c^0\bar{Lambda}_c^-)\times \BR(\Xi_c^0\to\Xi^-\pi^+)$ is measured to be $(2.04\pm0.59\pm0.26\pm0.53)\times 10^{-5}$, and $\BR(\Bzb\to\Xi_c^+\bar{\Lambda}_c^-)\times\BR(\Xi_c^+\to\Xi^-\pi^+\pi^+)$ is $(1.50\pm 1.07\pm 0.19 \pm 0.39)\times 10^{-5}$, where the uncertainties are statistical, systematic, and the uncertainty from the branching fraction $\BR(\Lambda_c^+\to\proton K^-\pi^+)$, respectively.

Quantum chromodynamics (QCD) is the modern theory of strong interactions. Quarks and antiquarks interact extit{via} gluons, the gauge bosons, and form well-know bound states, namely mesons and baryons. This non-Abelian gauge theory predicts the existence of unconventional states of quarks and gluons: Exotic hadrons. Their observation remains a difficult task since their properties are poorly known. Their theoretical study is a challenging task and will guide experimentalists in their work. This thesis is devoted to two main types of exotic hadrons: Hybrid mesons and glueballs. Hybrid mesons are mesons in which the gluon field is in an excited state. In constituent models, the excitation of the flux tube is interpreted in term of a constituent gluon. In this thesis, the connection between the two pictures, flux tube excitation and constituent gluon, is demonstrated. Using the technique of the auxiliary field, we reproduce, from the three-body system quark-antiquark-gluon, the excitations of the quark-antiquark potential observed in lattice QCD. We complete our study of mesons with exotic quantum numbers by performing a analysis of the low-lying spectrum. Glueballs are hadronic states with no valence quarks. Theoretical developments suggests that confined gluons gain a constituent mass inside glueballs. According to this, a gluon can be considered as a heavy spin-1 particle. Two- and three-gluon glueballs are then similar of heavy meson and baryon systems. We preformed a complete study of the low-lying spectrum of these glueballs. The comparison with the pure gauge results from lattice QCD showed a disagreement and led us to the conclusion that the gluon degree-of-freedom was not correctly taken into account. Indeed, the implementation of transverse gluons at the level of the wave functions solved this problem for two-gluon glueballs. For both systems, hybrid mesons and glueballs, we used semi-relativistic Hamiltonians since they remain valid for massless particles. A code in Gaussian basis was developed to solve our eigenvalue problems. For this purpose, we found the matrix elements between Gaussian functions for various operators.

This report explores a novel application of the initial state radiation (radiative return) method in an electron-positron collider, to measure the electron-positron annihilation into a neutral pion and a photon  reaction cross section at low energies. The challenge of using ISR events for analysis is due to the combinatorics issue presented by the extra photon(s) in the final state. Through measuring the cross section, access is gained to the time-like electromagnetic transition form factor (TFF) of the neutral pion. This can be used to constrain theoretical models of the hadronic light-by-light scattering contribution to the anomalous magnetic moment of the muon (AMM). The aim of this project was to determine if existing, or expected, data samples at the experiments KLOE-2 in Frascati and BES-III in Beijing could provide competitive results for the time-like TFF slope parameter. The analysis was performed through the construction of an event generator, where events were generated for three different reaction models. Considering the amount of data available at low energies, this study indicates that the ISR approach could be a viable option to enhance the data sample in the low energy region. The most promising experiment for further analysis is here indicated to be KLOE-2. Compared to tabulated values for the form factor slope parameter, the uncertainty retrieved here is roughly on the same order of magnitude or smaller. / I denna rapport behandlas en ny metod för analys av ISR-data från experiment vid elektron-positron-kolliderare, så som KLOE-2 och BES-III. Strålning i form av en eller flera fotoner som strålats ut från elektronen eller positronen innan kollision kallas ISR. Då en foton strålas ut  från initialtillståndet sänks reaktionens nominella energi. Detta möjliggör analys av reaktioner över ett kontinuerligt energispektrum. Utmaningen med ISR analys ligger i kombinatoriken som uppstår då det återfinns ytterligare fotoner i sluttillståndet för reaktionen.I rapporen beskrivs processen elektron-positron-annihilation till en neutral pion och en foton. Denna reaktion är intressant då kunskap om dess reaktionstvärsnitt ger tillgång till den elektromagnetiska formfaktorn för den neutrala pionen. Formfaktorn beskriver hur reaktionen i fråga avviker från en punkt-lik elektromagnetisk växelverkan. Den elektromagnetiska fromfaktorn för den neutrala pionen är i sin tur en viktig del i beräkningarna för det hadroniska bidraget till myonens anomala magnetiska moment (AMM). Eftersom AMM är experimentellt uppmätt till mycket god noggrannhet kan jämförelser med teoretiska modeller göras med hög precision.  Vid låg reaktionsenergi kan formfaktorn beskrivas med endast en parameter, lutningsparametern. Från Monte Carlo genererad ISR-data har i denna rapport lutningsparametern bestämts med noggrannhet som är likvärdig eller bättre än tabulerade värden, beroende på mängd analyserad data samt val av analysmetod.

Frankfurt (Main), Univ., Diss., 1998

Techn. Universiẗat, Diss., 2001--München.

Universiẗat, Diss., 1998--Frankfurt (Main).