Matching parton showers to NLO computations

TL;DR

The paper presents a method to attach parton showers to NLO jet cross sections in e+e- annihilation by marrying Catani–Seymour dipole subtraction with CKKW-like m-jet/m+1-jet matching. It develops a detailed PS/NLO framework where cross sections are partitioned into partial sigma_m with a jet-resolution parameter d_ini, and showers are incorporated through a reweighting factor W, dipole-based splitting functions, and dedicated Monte Carlo interface functions I and tilde{I}. The construction ensures the first two perturbative coefficients of each partial cross section are reproduced and avoids double counting between shower splittings and fixed-order contributions, achieving NLO accuracy for infrared-safe N-jet observables while yielding fully hadronized final states. The work also discusses Sudakov factors, kinematics, and practical considerations for selecting d_ini, and outlines alternative LO paths and future directions for extending to initial-state radiation and further shower sophistication. Overall, this PS/NLO matching framework integrates hard NLO corrections with realistic parton showers to provide reliable predictions across both perturbative and jet-structure regimes, with explicit formulas and steps for implementation.

Abstract

We give a prescription for attaching parton showers to next-to-leading order (NLO) partonic jet cross sections in electron-positron annihilation. Our method effectively extends to NLO the scheme of Catani, Krauss, Kuhn, and Webber for matching between m hard jets and (m+1) hard jets. The matching between parton splitting as part of a shower and parton splitting as part of NLO matrix elements is based on the Catani-Seymour dipole subtraction method that is commonly used for removing the singularities from the NLO matrix elements.}