This analysis studies the reaction ep → e′p′ϕ in the kinematical range 1.6 ≤ Q² ≤ 3.8 GeV² and 2.0 ≤ W ≤ 3:0 GeV at CLAS. After successful signal identification, total and differential cross sections are measured and compared to the world data set. Comparisons are made to the predictions of the Jean-Marc Laget(JML) model based on Pomeron plus 2-gluon exchange. The overall scaling of the total cross section was determined to be 1/Q^4.6±1.7 which is compatible within errors to the Vector Meson Dominance prediction of 1/Q⁴ as well as to the expected behavior of a quark and gluon exchange-dominated model described by Generalized Parton Distributions of 1/Q⁶. The differential cross section dσ/dφ was used to determine that the s-channel helicity conservation (SCHC) assumption is valid within the precision of the current data. SCHC leads to a simple expression for the decay angular distribution from which R, the ratio of the longitudinal to the transverse cross section, can be extracted. Under the assumption of SCHC, we determine R = 1.33 ± 0.18 at an average Q² of 2.21 GeV² which leads to a determination of the longitudinal cross section σ_L = 5.3 ± 1.3 nb for exclusive ϕ production. / Ph. D.

We studied the reaction 𝑒𝑝 → 𝑒′𝑝′𝜙 with a 4.2 GeV incident electron beam in the region of the electroproduction variables Q² from 0.7 to 2.2 GeV² and W from 2.0 to 2.6 GeV. The data were taken and analyzed at the Thomas Jefferson National Accelerator Facility. For the first time, we observe the expected t-slope dependence on Q² and Δ𝜏 in 𝜙 vector meson production. We find that the width of the forward 𝜙-meson diffraction peak increases rapidly as the interaction time decreases below cΔ𝜏 ≈ 1 fm. Within a simple optical model framework, the data show that 𝜙 meson has a smaller size than the 𝜌. The measured 𝜙 cross-section dependence on Q² is in a good agreement with previous measurements and well-described by the phenomenological Pomeron-exchange model. Our cross-section data do not favor the standard Vector Meson Dominance and 𝑠𝑠̅-knockout model predictions. From the angular distribution of the decay 𝜙 → 𝐾⁺𝐾⁻, assuming the 𝑠-channel helicity conservation, we extracted the longitudinal-to-transverse cross-section ratio, 𝑅, and Vector Meson Dominance scaling parameter, 𝜉², which are consistent with the previous measurements and the model expectations. / Ph. D.

Using data recorded by the CLEO II detector operating at the Upsilon(4S) resonance at the Cornell Electron Storage Ring, several properties of B mesons are measured using a partially reconstructed tag of the decay mode bar{B0} -> D*+ l- bar{nu}. Using 2.38 fb**{-1} of on-resonance data and the averaged B meson semileptonic branching fraction through inclusive lepton momentum spectrum obtained by previous CLEO analysis, we measure the B0 and B- semileptonic branching fraction to be (10.78 +/- 0.60 +/- 0.69)% and (10.25 +/- 0.57 +/- 0.65)% respectively, which yields the lifetime ratio tau_+/tau_0 = 0.950 +0.117-0.080 +0.091-0.068, assuming the equality of semileptonic partial branching width for bar{B0} and B-. With a larger dataset of 3.1 fb**{-1}, we measured the B0-bar{B0} mixing parameter chi_d to be 0.189 +/- 0.019 +/- 0.006. / Ph. D.

The TOF-spectrometer located at the proton accelerator COSY (Juelich) stands out for experimental versatility. This is due to its modular setup: about ten subdetectors can be be arranged to satisfy the individual requirements of specific experiments. However, this flexibility hampers the calibration and the data analysis, since for each new detector setup the software has to be adjusted as well. Therefore, a new analysis framework (TofRoot) has been developed. A set of concepts is used that enables teamwork and leads to an efficient data-analysis, even for different beamtimes. Using TofRoot, three reactions are analyzed - each for two different beam momenta (2950 MeV/c, 3200 MeV/c): Firstly, the elastic proton-proton scattering. It is used to determine the luminosity and to extract benchmark results for the detector performance. Secondly, the reaction pp->deutoron-piplus is studied. Total as well as differential cross sections are presented, which nicely fit into the word data set. Finally, the vector-meson production (omega) is investigated which is the scientific focus of this work. Here, the theoretical and experimental knowledge is presently rather scarce. However, the elementary reaction dynamics is needed as an inevitable prerequisite in many fields of physics; e.g. the short range part of the nucleon-nucleon force, the description of extremely dense matter, the strangeness content of nucleons. After a detailed description of the analysis strategies, total cross sections, angular distributions, and invariant-mass spectra are presented. Some of the findings are completely new, and all provide smaller experimental uncertainties with respect to the available word data set. Finally, the results are embedded into the existing body of data and their implication on the theoretical models is discussed. / Das TOF-Spektrometer am Protonen-Beschleunigerring COSY (Juelich) besticht durch seine experimentelle Vielseitigkeit, da der modulare Aufbau aus ca.~zehn Subdetektoren eine individuelle Anpassung an spezifische experimentelle Erfordernisse ermoeglicht. Diese Flexibilitaet erschwert jedoch die Kalibrierung und die Datenauswertung, da die Software nach jedem Umbau angepasst werden muss. Daher wurde das Analyseframework TofRoot entwickelt, welches durch einen Satz von Strategien eine effiziente und teamorientierte Auswertung ermoeglicht, sogar fuer verschiedene Strahlzeiten. Mit Hilfe von TofRoot wurden drei Reaktionskanaele analysiert, jeweils fuer zwei Strahlimpulse (2950 MeV/c, 3200 MeV/c): Zuerst die elastische Proton-Proton Streuung, welche der Luminositaetsbestimmung dient und an Hand derer die Guete des Detektorsystems und der Kalibration veranschaulicht wird. Anschliessend folgt die Reaktion pp->deuteron-piplus, bei der die extrahierten Winkelverteilungen und totalen Wirkungsquerschnitte sich widerspruchsfrei in die vorhandene Datenbasis einordnen. Schliesslich wird die Vektormesonenproduktion (omega) untersucht, die den wissenschaftlichen Fokus dieser Arbeit darstellt. In diesem Kanal ist die experimentelle Datenbasis duenn und die theoretische Beschreibung bislang unvollstaendig. Ein gutes Verstaendnis der omega-Produktionsdynamik ist aber unabdingbar fuer die theoretische Beschreibung vieler Felder moderner Physik, z.B. des kurzreichweitigen Teils der Nukleon-Nukleon-Wechselwirkung, extrem dichter Materie und des Strangenessanteils im Nukleon. Nach einer detailierten Beschreibung der Analysestrategien werden totale Wirkungsquerschnitte, Winkelverteilungen und Spektren invarianter Massen vorgestellt. Verglichen mit vorhandenen Daten sind alle Angaben mit kleineren experimentellen Unsicherheiten behaftet, und zum Teil erschliessen sie zuvor nicht zugaengliche Groessen. Abschliessend werden die Ergebnisse in die vorhandene experimentelle Datenbasis eingeordnet, und ihre Auswirkung auf theoretische Modelle wird diskutiert.

This thesis describes a search for the rare radiative decay of a B meson to two photons. where the charged congugate mode is implied throughout. These decays are highly suppressed in the Standard Model where the branching fraction is expected to be of order 10^-8. In some new physics scenarios this could be enhanced by up to an order of magnitude to 10^-7. Therefore an observation of a significant signal above the Standard Model prediction could be a sign of new physics. The search for this rare decay was performed using the data collected with the BaBar detector at the SLAC National Accelerator Laboratory PEP-II storage ring operating at the Upsilon(4S) resonance. The analysis uses a dataset with an integrated luminosity of 425.7 fb-1 corresponding to 467 million BB pairs. A signal yield of 21.3 +12.8 -11.8 events with a significance of 1.88 sigma was measured using an unbinned extended maximum likelihood fit. An upper limit on the branching fraction is set at the 90% confidence level of less than 3.2 times 10^-7. This is about two times more stringent than the best upper limit of less than 6.2 times 10^-7 published by the Belle collaboration. / text

The composite structure of the nucleon leads to a spectrum of excited states, or resonances, which contain important constraints on the dynamics and interactions of its constituents. A major world programme measuring meson photoproduction from the nucleon is currently under way to improve our knowledge of this fundamental spectrum. These new generation of measurements exploit polarisation degrees of freedom of the incident photon along with spin degrees of freedom in the target and recoiling nucleons. The meson photoproduction process can be described by 16 independent experimental observables. To fully constrain the four underlying complex photoproduction amplitudes requires the measurement of a least 8 of these. Measurements of double polarisation observables, where the photon beam and nucleon target are polarised are crucial to achieve this requirement. This thesis will present the analysis and extraction of the first preliminary measurement of the double polarisation observable. F in the single pion photoproduction reaction γ→ + p →n + π+ was undertaken to measure both F and T. The resulting measurement of polarisation observables from this reaction in conjunction with with those from the Pπ0 channel will provide stringent constraints on partial wave analyses aiming to extract precision information on the properties of the low lying nucleon resonances.

Elementary particles form hadrons through the strong interaction; one interpretation of a possible hadron bound-state is a hybrid meson which is composed of a quark-antiquark pair and gluonic content. Non-exotic hybrid mesons share spin <i>J</i>, parity <i>P</i> and charge conjugation <i>C</i> quantum numbers with quark-antiquark states while exotic hybrids do not. Aspects of particle physics, strong interactions, and quantum field theory necessary for calculating the correlation function for a hybrid meson will be reviewed. In particular, the perturbative part of the correlation function for a hybrid meson with <i>J</i>^PC=1^-- will be formulated in terms of Feynman rules and diagrams and calculated to next-to-leading order in the light (massless) quark case. Assuming the hybrid current renormalizes multiplicative, the next-to-leading order effects are found to be large, and are potentially important for future determinations of the light-quark non-exotic hybrid meson.

The role of scalar mesons in radiative vector meson decays is investigated. The effects of scalar-isoscalar f_{0}(980) and scalar-isovector a_{0}(980) mesons are studied in the mechanism of the radiative Phi-&gt / pi{+}pi{-}gamma and phi-&gt / pi{0}eta gamma decays, respectively. A phenomenological approach is used to study the radiative phi-&gt / pi{+}p{-}gamma decay by considering the contributions of sigma-meson, rho-meson and f_{0}-meson. The interference effects between different contributions are analyzed and the branching ratio for this decay is calculated. The radiative phi-&gt / pi{0}eta gamma decay is studied within the framework of a phenomenological approach in which the contributions of rho-meson, chiral loop and a_{0}-meson are considered. The interference effects between different contributions are examined and the coupling constants g_{phi a_{0} gamma} and g_{a_{0}K{+}K{-}} are estimated using the experimental branching ratio for the phi-&gt / pi{0}eta gamma decay. Furthermore, the radiative rho{0}pi{+}pi{-}gamma$ and rho{0}-&gt / pi{0}pi{0}gamma decays are studied to investigate the role of scalar-isoscalar sigma-meson. The branching ratios of the rho{0}-&gt / pi{+}pi{-}gamma and rho{0}-&gt / pi{0}pi{0}gamma decays are calculated using a phenomenological approach by adding to the amplitude calculated within the framework of chiral perturbation theory and vector meson dominance the amplitude of sigma-meson intermediate state. In all the decays studied the scalar meson intermediate states make important contributions to the overall amplitude.

Elementary particles form hadrons through the strong interaction; one interpretation of a possible hadron bound-state is a hybrid meson which is composed of a quark-antiquark pair and gluonic content. Non-exotic hybrid mesons share spin <i>J</i>, parity <i>P</i> and charge conjugation <i>C</i> quantum numbers with quark-antiquark states while exotic hybrids do not. Aspects of particle physics, strong interactions, and quantum field theory necessary for calculating the correlation function for a hybrid meson will be reviewed. In particular, the perturbative part of the correlation function for a hybrid meson with <i>J</i>^PC=1^-- will be formulated in terms of Feynman rules and diagrams and calculated to next-to-leading order in the light (massless) quark case. Assuming the hybrid current renormalizes multiplicative, the next-to-leading order effects are found to be large, and are potentially important for future determinations of the light-quark non-exotic hybrid meson.

<p>In recent years, the strangeness production reactions in NN collisions have attracted a considerable amount of interest. These reactions are expected to provide valuable information on the manifestation of Quantum chromodynamics (QCD) in the nonperturbative region. For example, the &phi; meson is expected to probe the admixture of strange quark pairs in the nucleon wave function. The near-threshold reactions are expected to provide valuable information about the meson-meson, meson-baryon,</p><p>and hyperon-nucleon interactions.</p><p>We report the differential and total cross sections for the pp &rarr; ppKK/&phi; reaction at Tp= 2.567 (below the &phi; meson threshold) and 2.83 GeV (above the &phi; meson threshold). We use detailed model descriptions to fit a variety of one dimensional distributions in order to separate the pp &rarr; pp&phi; cross section from that of non- &phi; production. The differential spectra show that higher partial waves represent the majority of the pp &rarr; pp &phi; total cross section at an excess energy of 76 MeV, whose energy dependence would then seem to require some s-wave &phi;p enhancement near threshold. On the other hand, strong preferences to the low Kp and Kpp invariant masses are observed in non- kaon pair productions. The cusp effect in the KK distribution at the K0 K0 threshold is clear and some evidence is also found for coupling between the Kp and K0n channels. Beside of the mentioned reactions, we also show the preliminary results for the search for a possible Kpp bound state in the pp &rarr; pK&Lambda; reaction at Tp=2.567 GeV.</p> / Dissertation