QCD parton showers and NLO EW corrections to Drell-Yan
P. Richardson, R. R. Sadykov, A. A. Sapronov, M. H. Seymour, P. Z. Skands
TL;DR
The paper demonstrates a practical interface that combines complete NLO electroweak corrections from the SANC framework with QCD parton-shower Monte Carlos (Pythia8 and Herwig++), including crucial photon-induced initial-state contributions. It implements backward evolution of photons in both shower programs, enabling realistic Drell–Yan predictions at the LHC with EW effects embedded in the showering. Validation shows reasonable agreement across setups, while residual differences between shower algorithms persist, underscoring the importance of matching to higher-order QCD matrix elements for jet-rich regions. The work provides a pathway toward more precise, EW-consistent DY simulations and sets the stage for future QCD-EW matching developments and comparisons with POWHEG-based approaches.
Abstract
We report on the implementation of an interface between the SANC generator framework for Drell-Yan hard processes, which includes next-to-leading order electroweak (NLO EW) corrections, and the Herwig++ and Pythia8 QCD parton shower Monte Carlos. A special aspect of this implementation is that the initial-state shower evolution in both shower generators has been augmented to handle the case of an incoming photon-in-a-proton, diagrams for which appear at the NLO EW level. The difference between shower algorithms leads to residual differences in the relative corrections of 2-3% in the p_T(mu) distributions at p_T(mu)>~50 GeV (where the NLO EW correction itself is of order 10%).