Gerhard A. Schuler

Combined QED and QCD radiative effects in deep inelastic lepton-proton scattering: the Monte Carlo generator DJANGO6

We describe the event generator DJANGO6, which simulates deep inelastic lepton-proton scattering including both QED and QCD radiative effects. DJANGO6 is an interface of the programs HERACLES 4.4 and LEPTO 6.1. The LUND-string fragmentation is used to obtain the complete hadronic final state. DJANGO6 is an update, which now also allows to use the matrix element options of LEPTO, which means that non-logarithmic corrections of O(αs) can be taken into account.

Parton distributions of the virtual photon

We propose a generic ansatz for the extension of parton distributions of the real photon to those of the virtual photon. Alternatives and approximations are studied that allow closed-form parametrizations.

Towards a complete description of high-energy photoproduction

A real photon has a dual nature, as a pointlike elementary particle and as a qq fluctuation, in the latter case often with hadron-like properties. Therefore high-energy γp interactions have a rich and not yet well explored structure. In this paper, we propose a consistent formulation, which is based on a subdivision of the total cross section into three distinct event classes: direct, VMD and anomalous. The VMD class, in its turn, contains the subclasses familiar from hadron-hadron physics. Within this approach, we calculate all the partial cross sections. Many other aspects of the event classes are also considered, such as proton and photon structure functions, jet rates and beam remnant structures. A major role is played by two distinct transverse momentum cut-off scales, which separate the classes. When all the ingredients are put together, we obtain a detailed model for photoproduction events. In order to test this approach, we also propose several alternative scenarios, each of which emphasizes different aspects of the photon. Predictions are presented for HERA events.

Low- and High-Mass Components of the Photon Distribution Functions *

AbstractThe structure of the general solution of the inhomogeneous evolution equations allows the separation of a photon structure function into perturbative (“anomalous”) and non-perturbative contributions. The former part is fully calculable, and can be identified with the high-mass contributions to the dispersion integral in the photon mass. Properly normalized “state” distributions can be defined, where the

Two-photon physics with GALUGA 2.0

\gamma \to q\bar q

Systematics of quarkonium production

splitting probability is factored out. These state distributions are shown to be useful in the description of the hadronic event properties, and necessary for a proper eikonalization of jet cross sections. Convenient parametrizations are provided both for the state and for the full anomalous parton distributions. The non-perturbative parts of the parton distribution functions of the photon are identified with the low-mass contributions to the dispersion integral. Their normalizations, as well as the value of the scaleQ0 at which the perturbative parts vanish, are fixed by approximating the low-mass contributions by a discrete, finite sum of vector mesons. The shapes of these hadronic distributions are fitted to the available data onF2γ(x, Q2). Parametrizations are provided forQ0=0.6 GeV andQ0=2 GeV, both in the DIS and the

Meson-photon transition form factors and resonance cross-sections in e+e− collisions

\overline {MS}