H. G. Dosch

Nonperturbative QCD treatment of high-energy hadron-hadron scattering.

Total cross sections and logarithmic slopes of the elastic scattering cross sections for different hadronic processes are calculated in the framework of the model of the stochastic vacuum. The relevant parameters of this model, a correlation length and the gluon condensate, are determined from scattering data, and found to be in very good agreement with values coming from completely different sources of information. A parameter-free relation is given between total cross sections and slope parameters, which is shown to be remarkably valid up to the highest energies for which data exist.

Vector meson leptoproduction and nonperturbative gluon fluctuations in QCD

We present a nonperturbative QCD calculation of diffractive vector meson production in virtual photon nucleon scattering at high energy. We use the nonperturbative model of the stochastic QCD vacuum which yields linear confinement and makes specific predictions for the dependence of high-energy scattering cross sections on the hadron size. Using light cone wave functions of the photon and vector mesons, we calculate electroproduction cross sections for {rho}, {omega}, {phi}, and J/{psi}. We emphasize the behavior of specific observables such as the ratio of longitudinal to transverse production cross section and the t dependence of the differential cross section. {copyright} {ital 1997} {ital The American Physical Society}

Semileptonic D decay into scalar mesons: A QCD sum rule approach

Semileptonic decays of D mesons into scalar hadronic states are investigated. Two extreme cases are considered: (a) the meson decays directly into an uncorrelated scalar state of two mesons and (b) the decay proceeds via resonance formation. QCD sum rules including instanton contributions are used to calculate total and differential decay rates under the two assumptions.

Decomposition of the QCD string into dipoles and unintegrated gluon distributions

We present the perturbative and non-perturbative QCD structure of the dipole-dipole scattering amplitude in momentum space. The perturbative contribution is described by the two-gluon exchange and the non-perturbative contribution by the stochastic vacuum model which leads to confinement of the quark and antiquark in the dipole via a string of color fields. This QCD string gives important nonperturbative contributions to high-energy reactions. A new structure different from the perturbative dipole factors is found in the string-string scattering amplitude. The string can be represented as an integral over stringless dipoles with a given dipole number density. This decomposition of the QCD string into dipoles allows us to calculate the unintegrated gluon distribution of hadrons and photons from the dipole-hadron and dipole-photon cross section via

Semileptonic inclusive B decays and the determination of ||Vub|| from QCD sum rules.

|{k}_{\ensuremath{\perp}}|

Odd CP contributions to diffractive processes

factorization.

Semileptonic inclusive [ital B] decays and the determination of [vert bar][ital V][sub [ital u][ital b]][vert bar] from QCD sum rules

We calculate the electron spectrum of semileptonic decays of B mesons into noncharmed hadrons. The shape of the spectrum obtained from QCD sum rules is in general agreement with quark model calculations. At high electron energies the decrease of the spectrum is less steep than predicted by Altarelli et al. Our analysis yields a total decay rate Γ(B→Xueν )=(6.8±2.0)×1013|Vub|2 s-1. For the spectrum integrated over electron energies in the interval 2.4 GeV≤Ee≤2.6 GeV in the laboratory frame we obtain Γ(B→Xueν )=(5.0±1.6)×1012|Vub|2 s-1. Estimating all sorts of theoretical uncertainties, we obtain |Vub|=0.003±0.001 for the b→u weak transition matrix element from the new CLEO data.

γ(∗)γ(∗)-reactions at high energies

We investigate contributions to diffractive scattering, which are odd under C- and P-parity. Comparison of p-

Roles of photon and vector meson wave functions in photo‐ and electro‐production processes

\bar p

Non-perturbative QCD treatment of high energy hadron-hadron scattering

and p-p scattering indicates that these odderon contributions are very small and we show how a diquark clustering in the proton can explain this effect. A good probe for the odderon exchange is the photo- and electroproduction of pseudo-scalar mesons. We concentrate on the pi^0 and show that the quasi elastic pi^0-production is again strongly suppressed for a diquark structure of the proton whereas the cross sections for diffractive proton dissociation are larger by orders of magnitude and rather independent of the proton structure.