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The cross section for coherent $\omega$-meson photoproduction off the deuteron has been measured for the first time as a function of the momentum transfer $t = (P_{\gamma}-P_{\omega})^2$ and photon energy $E_{\gamma}$ using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The cross sections are measured in the energy range $1.4 < E_{\gamma} < 3.4$ GeV. A model based on $\omega-N$ rescattering is consistent with the data at low and intermediate momentum transfer, $|t|$. For $2.8 < E_{\gamma} < 3.4$ GeV, the total cross-section of $\omega-N$ scattering, based on fits within the framework of the Vector Meson Dominance model, is in the range of 30-40 mb., Comment: 8 pages, 5 figures

Two sets of experiments have been performed with the WASA detector at COSY. The intention is to compare the quality of the data between the pd->^3He omega and pp->pp omega reactions, in the sense of a feasibility and background study for omega -> pi^0e^+e^- decays. The aim of the physics program is to determine the transition form factor of the omega meson which does not agree with standard Vector Meson Dominance. As a first step towards the omegapi transition form factor, we study the decay with a real photon, omega -> pi^0gamma. The status of the analysis is presented.

We present a new, model-independent method to analyze radiative decays of mesons to a vector, isovector pair of pions of invariant mass square below the first significant pion-pion threshold in the vector channel. It is based on a combination of chiral perturbation theory and dispersion theory. This allows for a controlled inclusion of resonance physics without the necessity to involve vector meson dominance explicitly. As an example, the method is applied to an analysis of the reactions eta -> pi+ pi- gamma and eta'->pi+ pi- gamma., Comment: 16 pages, 4 figures

Quasielastic production of J / ψ mesons has been measured in muon interactions with hydrogen, deuterium, carbon and tin targets at incident muon energies of 200 and 280 GeV. The hydrogen and deuterium data were used to study the transverse momentum distribution of the J / ψ 's. These data have been analysed together with previously published ϱ 0 data in the framework of the vector meson dominance model. The radii of the Jψ and the ϱ 0 as well as the total J / ψ - N and ϱ 0 - N cross sections were deduced. From the tin and carbon data the ratio of the quasielastic J / ψ production cross sections, R qe (Sn/C), has been extracted and found to be less than unity. In the Glauber approach this suppression can be related to the J / ψ absorption probability in nuclei. The suppression is also compared to those predicted by various colour transparency models.

It is shown that the relative sign between the $NN\omega$ and $\pi\rho\omega$ coupling constants can be determined most sensitively from $\omega$ production processes in $NN$ collisions. Recent data on these reactions clearly favor the sign of the $\pi\rho\omega$ coupling constant which is opposite to that inferred from studies of the photoproduction reaction in combination with the vector meson dominance assumption and used by many authors. Implication of this finding in the description of other reactions is discussed., Comment: 6 pages, 4 figures, REVTeX, to be published in Phys. Lett. B

Experimental results from HERA on diffractive vector meson production and their theoretical interpretation within microscopic QCD are reviewed with an emphasis on the BFKL color dipole and kt-factorization approaches., Comment: 178 pages including 78 figures

We estimate the rates for radiative transitions of the lightest scalar mesons f_0(980) and a_0(980) to the vector mesons rho and omega. We argue that measurements of the radiative decays of those scalar mesons can provide important new information on their structure., Comment: 20 pages, 5 figures; appendix added, to be published in Phys. Rev. C

Universität Hamburg, Diss., 2003; 154 pp., (2003). doi:10.3204/DESY-THESIS-2003-040, Published by Deutsches Elektronen-Synchrotron, DESY, Hamburg

Humboldt Universität Berlin, Diss., 2002; 115 pp., (2002). doi:10.3204/DESY-THESIS-2002-018, Published by Deutsches Elektronen-Synchrotron, DESY, Hamburg

Columbia University, Diss., 2002; 162 pp. (2002). = Columbia University, Diss., 2002

Universität Hamburg, Diss., 2001; 135 pp. (2001). = Universität Hamburg, Diss., 2001

8 pp. (2000)., A parametrization of the real photon structure function $F_2^\gamma$ in the low $Q^2$, low $x$ region is formulated. It includes both the vector meson dominance (VMD) and the QCD components, the latter suitably extrapolated to the low $Q^2$ region and based on arbitrary parton distributions in the photon. The parametrization used together with the Gluck, Reya, and Vogt (GRV) and Gluck, Reya, and Schienbein (GRS) parton densities describes reasonably well the existing high energy data on $F_2^\gamma$, $\sigma_{\gamma\gamma}$, and the low $Q^2$ data on $\sigma_{\gamma^* \gamma}$. Predictions for $\sigma_{\gamma\gamma}$ and for $\sigma_{\gamma^*\gamma}$ for energies which may become accessible in future linear colliders are also given.

Universität Hamburg, Diss., 1998; 264 pp. (1998). = Universität Hamburg, Diss., 1998

DESY, Diplomarbeit, 1998; 46 pp., (1998). doi:10.3204/PUBDB-2016-02733

Universität Hamburg, Diss., 1998; 133 pp., (1998). doi:10.3204/PUBDB-2016-02640, We calculate the leading power corrections to the decay rates, distributions and hadronic spectral moments in rare inclusive \bxsll decays in the standard model, using heavy quark expansion (HQE) in $(1/m_b)$ and a phenomenological model implementing the Fermi motion effects of the b-quark bound in the B-hadron. We include next-to-leading order perturbative QCD corrections and work out the dependences of the spectra, decay rates and hadronic moments on the model parameters in either HQE and the Fermi motion model. In the latter, we take into account long-distance effects via $B \to X_s +(J/\psi, \psi^\prime,...) \to X_s \ell^+ \ell^- $ with a vector meson dominance ansatz and study the influence of kinematical cuts in the dilepton and hadronic invariant masses on branching ratios, hadron spectra and hadronic moments. We present leading logarithmic QCD corrections to the $b \to s \gamma\gamma$ amplitude. The QCD perturbative improved $B_{s}\to\gamma\gamma$ branching ratio is given in the standard model including our estimate of long-distance effects via $B_s \to \phi \gamma \to \gamma \gamma$ and $B_s \to \phi \psi \to \phi \gamma \to \gamma \gamma$ decays. The uncertainties due to the renormalization scale and the parameters of the HQE inspired bound state model are worked out.

University of Warsaw, Diss., 1996; 95 pp. (1996). = University of Warsaw, Diss., 1996

8 pp. (1994)., Recently, the ZEUS Collaboration has reported on several remarkable properties of events with a large rapidity gap in deep inelastic scattering. We suggest that the mechanism underlying these events is the scattering of electrons off lumps of wee partons inside the proton. Based on an effective lagrangian approach the Q 2 -, x - and W -distributions are evaluated. For sufficiently small invariant mass of the detected hadronic system, the mechanism implies leading twist behaviour. The x - and W -distributions are determined by the Lipatov exponent which governs the behaviour of parton densities at small x .

24 pp. (1991)., We have measured the cross section and $Q^2$-dependence of the reaction γγ→ multihadrons, using the CELLO detector at DESY, for visible final-state masses between 4 and 9 GeV. The data are well fitted by an incoherent sum of Generalised Vector Meson Dominance and Quark Parton Model terms, but at lowQ2 require the addition of a third component which resembles the QPM but is less two-jet-like. With and without this term, the GVDM cross section atQ2=0 is found to be 200±20 and 250±25 nb, respectively.

42 pp. (1990).