KKMChh: matching CEEX photonic ISR to a QED-corrected parton shower

TL;DR

KKMChh is a Monte Carlo tool that integrates CEEX formalism for photon radiation with QED-corrected PDFs to improve precision in Z boson production modeling in hadron collisions.

Contribution

It introduces a new method for matching initial state radiation in KKMChh to QED-corrected PDFs, enhancing accuracy in electroweak calculations.

Findings

QED-corrected PDFs improve the modeling of initial state radiation.

The new matching procedure aligns KKMChh with QED effects in PDFs.

Comparison shows better consistency with electroweak corrections.

Abstract

KKMChh adapts the CEEX (Coherent Exclusive Exponentiation) formalism of the Monte Carlo Program KKMC for Z boson production and decay to hadron scattering. Amplitude-level soft photon exponentiation of initial and final state radiation, together with initial-final interference, is matched to a perturbative calculation to second order next-to-leading logarithm, and electroweak corrections to the hard process are included via DIZET. The first release of KKMChh included complete initial state radiation calculated with current quark masses. This version assumes idealized pure-QCD PDFs with negligible QED contamination. Traditional PDFs neglect QED evolution but are not necessarily free of QED influence in the data. QED-corrected PDFs provide a firmer starting point for precision QED work. We describe a new procedure for matching KKMChh's initial state radiation to a QED-corrected PDF, and compare this to earlier approaches.