Multi-photon Monte Carlo event generator KKMCee for lepton and quark pair production in lepton colliders

TL;DR

The paper introduces KKMCee 5.00.2, a modern C++ Monte Carlo event generator for lepton and quark pair production in electron-positron collisions, enhancing precision and compatibility for future collider experiments.

Contribution

It presents a re-written C++ version of KKMC with improved algorithms, new interfaces, and extended features for high-precision simulations at future lepton colliders.

Findings

Rewritten source code in C++ for better integration.

Includes higher order QED and weak corrections.

Provides interfaces for parton showers and detector simulation.

Abstract

We present the {\tt KKMCee 5.00.2} Monte Carlo event generator for lepton and quark pair production for the high energy electron-positron annihilation process. It is still the most sophisticated event generator for such processes. Its entire source code is re-written in the modern C++ language. It reproduces all features of the older \kkmc\ code in Fortran 77. However, a number of improvements in the Monte Carlo algorithm are also implemented. Most importantly, it is intended to be a starting point for the future improvements, which will be mandatory for the future high precision lepton collider projects. As in the older version, in addition to higher order QED corrections, it includes so-called \order{\alpha^{1.5}} genuine weak corrections using a version of the classic {\tt DIZET} library and polarized $\tau$ decays using {\tt TAUOLA} program. Both {\tt DIZET} and {\tt TAUOLA} external libraries are still in Fortran 77. In addition, a {\tt HEPMC3} interface to other MC programs, like parton showers and detector simulation, replaces the older {\tt HepEvt} interface. The {\tt HEPMC3} interface is also exploited in the implementation of the additional photon final state emissions in $\tau$ decays using an external {\tt PHOTOS} library rewritten in C.