Initial-state showering based on colour dipoles connected to incoming parton lines
Jan-Christopher Winter, Frank Krauss
TL;DR
This work extends the Colour Dipole Model to a fully perturbative initial-state radiation framework by formulating emissions as colour-dipole splittings linking incoming partons. It defines a generalized, Lorentz-invariant kinematic scheme with unified evolution variables and derives dipole splitting cross sections for FF, II, and FI dipoles, incorporating PDFs and recoil handling. The complete shower algorithm is built around a Sudakov form factor and a veto-based Monte Carlo emission generation, with scale choices and initializations tailored to different hard processes, and is implemented in SHERPA. First results across $e^+e^-$ annihilation, Drell–Yan, and jet production show encouraging agreement with data and other models, highlighting the approach’s potential for improved coherence and matrix-element matching in hadron-collider physics.
Abstract
A parton-shower model for hadronic collisions based on the emission properties of QCD dipoles is proposed. This proposal therefore extends the well-known radiation pattern of pure final-state colour dipoles to QCD initial-state radiation, both of which are treated perturbatively. Corresponding dipole splitting functions are derived and the kinematics of all dipole splittings is discussed. Application to hadron production in electron-positron annihilation, to Drell-Yan lepton-pair and QCD jet production yields encouraging results.