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.

No description available.

The null result of December 2004 Sub-threshold photoproduction of J/$psi$ experiment has motivated this thesis. This monte-carlo predicts the cross-section for sub-threshold photoproduction process and provides an insight on the cross-section range of these processess. The experiment was also conducted as a calibration run for Omega and Eta mesons for the verification of correctness of experimental procedure. The results from this experiment are compared with the monte-carlo simulation for the number of omega meson events. This is primarily done as the models for photoproduction of omega meson are well tested. The monte-carlo provides satisfactory results for the photoproduction models and with a crude a spectrometer model predicts the number of events which are off by a factor less than two. A refined model from Jefferson lab will eliminate this discrepancy.

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.

The environment inside the atomic nucleus is one of the most fascinating arenas for the study of quantum chromodynamics (QCD). The strongly-interacting nature of the nuclear medium affects the nature of both QCD processes and the quark-gluon structure of hadrons, allowing several unique aspects of the strong nuclear force to be investigated in reactions involving nuclear targets. The research presented in this dissertation explores two aspects of nuclear QCD: firstly, the partonic structure of the nucleus itself; and secondly, the use of the nucleus as a micro-laboratory in which QCD processes can be studied. The partonic structure of the nucleus is calculated in this work by deriving and utilizing a convolution formula. The hadronic structure of the nucleus and the quark-gluon structure of its constituent nucleons are taken together to determine the nuclear partonic structure. Light cone descriptions of short range correlations, in terms of both hadronic and partonic structure, are derived and taken into account. Medium modifications of the bound nucleons are accounted for using the color screening model, and QCD evolution is used to connect nuclear partonic structure at vastly different energy scales. The formalism developed for calculating nuclear partonic structure is applied to inclusive dijet production from proton-nucleus collisions at LHC kinematics, and novel predictions are calculated and presented for the dijet cross section. The nucleus is investigated as a micro-laboratory in vector meson photoproduction reactions. In particular, the deuteron is studied in the break-up reaction γd → Vpn, for both the ϕ(1020) and J/ψ vector mesons. The generalized eikonal approximation is utilized, allowing unambiguous separation of the impulse approximation and final state interactions (FSIs). Two peaks or valleys are seen in the angular distribution of the reaction cross section, each of which is due to an FSI between either the proton and neutron, or the produced vector meson and the spectator nucleon. The presence and size of the latter FSI valley/peak contains information about the meson-nucleon interaction, and it is shown that several models of this interaction can be distinguished by measuring the angular distribution for the deuteron breakup reaction.

No description available.

No description available.

The radiative &amp / #969 / &amp / #8594 / &amp / #960 / 0&amp / #960 / 0&amp / #947 / , &amp / #961 / &amp / #8594 / &amp / #960 / 0&amp / #960 / 0&amp / #947 / , &amp / #969 / &amp / #8594 / &amp / #960 / +&amp / #960 / &amp / #8722 / &amp / #947 / and &amp / #961 / &amp / #8594 / &amp / #960 / +&amp / #960 / &amp / #8722 / &amp / #947 / decays are studied by adding the effect of vector meson mixing to the amplitude of these decays. For the above decays we consider only &amp / #961 / &amp / #8722 / &amp / #969 / mixing. In addition to the &amp / #961 / &amp / #8722 / &amp / #969 / mixing, we also analyse the contributions coming from different intermediate states to examine the decay mechanism of these decays in a phenomenological framework. For &amp / #969 / &amp / #8594 / &amp / #960 / 0&amp / #960 / 0&amp / #947 / decay, we consider the contributions of the &amp / #961 / -meson and &amp / #963 / -meson intermediate states and of the kaon-loop, and for the &amp / #961 / &amp / #8594 / &amp / #960 / 0&amp / #960 / 0&amp / #947 / decay we calculate the amplitude using the contributions of the &amp / #969 / -meson and &amp / #963 / -meson intermediate states and pion-loop. Moreover, the radiative &amp / #969 / &amp / #8594 / &amp / #960 / +&amp / #960 / &amp / #8722 / &amp / #947 / decay is studied by considering the contributions of &amp / #963 / -meson and &amp / #961 / -meson intermediate states and the decay &amp / #961 / &amp / #8594 / &amp / #960 / +&amp / #960 / &amp / #8722 / &amp / #947 / is investigated by taking into account the contributions of bremmsstrahlung, pion-loop and &amp / #963 / - meson intermediate state amplitude. We also estimate the coupling constant g&amp / #969 / &amp / #963 / &amp / #947 / utilizing the latest experimental value of the branching ratio &amp / #969 / &amp / #8594 / &amp / #960 / 0&amp / #960 / 0&amp / #947 / .