Colour: A Computer Program for QCD Colour Factor Calculations

A computer program for evaluating colour factors of QCD Feynman diagrams is presented, and illustrative examples on how to use the program to calculate non trivial colour factors are given. The program and the discussion in this paper is based on a diagrammatic approach to colour factors.Comment: 12 pages, Latex and postscript figures in an uuencode packag

LDCMC version 1.0

We present the LDCMC program implementing the Linked Dipole Chain model for deeply inelastic ep scattering within the framework of the Ariadne event generator. 1 Introduction The large energies of the colliding positron and proton at the HERA accelerator enables a detailed study of the proton structure. Data is available for a wide kinematical region from very large virtualities Q 2 of the photon probe, to very small values of the Bjorken x-variable. We will here present a Monte Carlo event generator which covers the whole of this kinematical region and gives a theoretically well founded description of both the proton structure and the hadronic final state properties in the collision events. Theoretical description of the proton structure has since long been available through the DGLAP evolution equations [1], valid for large values of Q 2 , and the BFKL equations [2] which cover the very soft part of the proton structure (the x ! 0 limit). A third theoretical approach has been..

The Linked Dipole Chain Monte Carlo

We present an implementation of the Linked Dipole Chain model for deeply inelastic ep scattering into the framework of the Ariadne event generator. Using this implementation we obtain results both for the inclusive structure function as well as for exclusive properties of the hadronic final state. The original publication was based on results from an implementation containing an error. In this revised version this error has been corrected, some of the beyond leading-log assumptions have been revised and so have some of the results. 1 Introduction With the HERA collider, a new kinematical regime has been opened up for studying deeply inelastic ep scattering (DIS) on partons carrying a very small momentum fraction x of the proton. Much theoretical and experimental effort has been made to increase our understanding of the dynamics of such small-x partons, and much progress has been made, although many problems still need to be solved. On the theoretical side, a major issue is how to ..

The Linked Dipole Chain Monte Carlo

. We are working on a full-scale Monte Carlo simulation program [1] for describing e-p collisions. This MC is based on the Linked Dipole Chain (LDC) model which, in turn, is a modification and generalization of the CCFM model. Here I will start by explaining the basic model, then describe the MCimplementation and finish with some preliminary results. INTRODUCTION Generally in perturbative e-p DIS models one assumes that a parton is picked up from a proton parton distribution at low virtuality. After some perturbative emissions, called Initial State Bremsstrahlung (ISB), one ends up with a quark which interacts with the electron. More partons are then emitted from the initial ladder and those are called Final State Bremsstrahlung (FSB). In a realistic model one must also include a hadronization process where the partons become jets of colour singlet hadrons. With the Linked Dipole Chain (LDC) model [2], one can perform both the ISB, to evaluate the structure function or the cross secti..

The Metropolis algorithm for on-shell four momentum phase space

We present several implementations of the Metropolis method, an adaptive Monte Carlo algorithm, which allow for the calculation of multi-dimensional integrals over arbitrary on-shell four-momentum phase space. The Metropolis technique reveals itself very suitable for the treatment of high energy processes in particle physics, particularly when the number of final state objects and of kinematic constraints on the latter gets larger. We compare the performances of the Metropolis algorithm with those of other programs widely used in numerical simulations.Comment: 28+3 pages, To appear in Computer Physics Communications. One proof revised, to appear as Erratum in CP

The LDC Event Generator

: We describe briefly a Monte Carlo implementation of the Linked Dipole Chain model and an interface of it to the Ariadne program for simulation of complete DIS events at HERA. Using this new tool we make some preliminary comparisons to HERA data and find reasonable agreement. The Linked Dipole Chain model We here give a brief sketch of the properties of the Linked Dipole Chain (LDC) model, developed by the Lund group. A more detailed description is presented in Refs. [1, 2]. The model is a reformulation and generalization of the formalism developed by Ciafaloni, Catani, Marchesini and Fiorani (CCFM) [3], which interpolates smoothly between the DGLAP and BFKL regions. In the CCFM model there is a specific recipe, which for each possible final state specifies a separation of the produced gluons in what can be called initial-state and final-state radiation. The initial state radiation can be described by a ladder diagram as in Fig. 1. Each set of final states, specified by a definite la..