The Linked Dipole Chain Monte Carlo

TL;DR

This paper introduces the first Monte Carlo implementation of the Linked Dipole Chain (LDC) model for small-x DIS, reformulating the CCFM evolution to remove the non-eikonal form factor and to describe exclusive hadronic final states. The approach couples ISB and FSB within a colour-dipole cascade, yielding simple emission weights and an interpolation between DGLAP and BFKL across kinematic regimes. Through fits to F2 data and comparisons with hadronic final-state observables at HERA, the authors demonstrate that unordered ISB emissions are important but much of the forward activity can be captured by DGLAP-like chains with certain photon-end kinematics. While informative, the work highlights uncertainties in input parton densities and Sudakov regularization, and it outlines future enhancements to tighten these predictions and extend the framework to broader collision environments.

Abstract

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.)

Figures (11)

• Figure 1: Lepton proton scattering with $n$ perturbative ISB emissions. The emitted ISB partons are denoted $\{ q_i \}$ and the propagators are denoted $\{ k_i \}$.
• Figure 2: CCFM $\rightarrow$ LDC: The emission $q$ is regarded as ISB in the CCFM model but in LDC model it is regarded as FSB. This is illustrated (above) with fan diagrams and (below) in a $\log p_\perp^2-$rapidity diagram. Rapidity here is defined as $\log (p_+/p_\perp )$ and the dashed lines indicate equal $p_+$.
• Figure 3: The decrease of log of the parton density with $\ln p_\perp^2$ at a certain rapidity, for different $x$-values, for running (solid line) and constant (dashed line) coupling.
• Figure 4: (a) The phase space of parton emission from a $q-{\bar{q}}$ pair. (b) After the first emission, the phase space is split into two triangle which radiate gluons independently, but under a $p_\perp$-ordering condition. (c) An event with four emissions.
• Figure 5: (a) ISB emissions plotted in a dipole triangle. (b) The solid circles are ISB emissions and the dashed circles are FSB emissions.