Since the KKMC program was published for the first time over 20 years ago, it has gained popularity and was exploited in a broad spectrum of applications. The core part of the program itself did not change much. In contrast, some of the libraries have evolved substantially.The aim of this publication is to archive four versions, alternative to the one published 20 years ago versions of the electroweak libraries (or just parameter initialization versions), which were instrumental for the precision Standard Model calculation from the end of LEP era till now and for the sake of the future applications/comparisons for the future electron–positron colliders, in particular for the FCC-ee related studies. These electroweak libraries are useful for the hadron collider applications as well, for instance for KKMC-hh or TauSpinner projects. New version program SummaryProgram Title: KKMCCPC Library link to program files:http://dx.doi.org/10.17632/8w4vrpttpc.1Licensing provisions: GPL-3.0Programming language: FORTRAN 77Journal reference of previous version: Comput. Phys. Commun. 130 (2000) 260Does the new version supersede the previous version?: NoReasons for the new version: The basic reason is the upgrade of the DIZET electroweak library. The KKMC Monte Carlo [1] is designed to simulate two fermion production process in the electron–positron colliders, e+e−→2fnγ, (f=μ,τ,u,d,c,s,b,ν,f≠e ). It is armed with the most advanced QED matrix element based on the coherent exclusive exponentiation (CEEX) of the initial and final state bremsstrahlung, valid up to the highest FCC-ee energies [2,3]. The detailed description of how to use the KKMC Monte Carlo program can be found in Ref. [1]. The physics content of the version 4.16 which we will use in the present paper as a reference is explained in Ref. [3]. For further details see references therein and KKMC webpage [4], where up to date development versions of KKMC can also be found. For novel applications and for further references see e.g. Ref. [5]. The differences of the new KKMC program versions, with respect to the published ones, are not big – the structure of the program and user interface have not changed. In particular the methodology of interfacing electroweak corrections calculation to the core KKMC code still follows the prescription given in Ref. [1]. Now, when the FCC effort takes momentum, it is a good time to archive the KKMC program, its cross-checks and documentation, for the future references. The important first step in this direction is the proper archiving of the variants of electroweak libraries used in KKMC program over the past two decades and at present. Let us keep in mind that the recently developed offspring program KKMC-hh [6] for Z production in hadron collider applications also uses the same electroweak (EW) libraries. In addition, TauSpinner of Ref. [7] exploits EW results obtained from the EW libraries update presented here. The present paper may be treated as an appendix to [1] rather than as an independent publication. Already nowadays, work on experimental tests of Standard Model in ATLAS turned out to pose some challenges for proper adjustment of electroweak software and to conventions of LEP 1 and LEP 2 times [8]. This experience contributes also to our motivation. This may be even more important in the future, when expertise of people involved in LEP efforts will be less available than now.Summary of revisions: In the revision are included three versions of the DIZET electroweak library: the original version 6.21 but with updated input parameters, version 6.42 with the updated vacuum polarization and the latest version 6.45. The electroweak library DIZET version 6.21 [9,10] was installed in the KKMC from the very beginning in versions of Refs. [1,3]. Since then the KKMC code includes WW and ZZ boxes and other non-QED corrections such as top loop/vertex corrections important for precision predictions. The basics of the original DIZET interface did not require modifications and is the same until the present days.11Note however that the interface of the DIZET library to the function calculating the contribution of low energy e+e−→hadrons data varies between version 6.21 and later versions. Luckily, the pretabulation procedure (interface) of the electroweak form factors, that is in the form of the lookup tables in the disk files, used in KKMC offers an easy way for the upgrades with the newer versions of the DIZET library. In the KKMC program these lookup tables can be also optionally produced in flight, instead of being stored in text disk files. However, for the sake of archivization, the version with lookup tables on the disk is included in the present distribution because it demonstrates manifestly how well the EW library is independent from the rest of the MC code and also has some practical advantages — the electroweak initialization can be more easily adjusted locally for each electroweak library variant.Using the pretabulating algorithm for the DIZET version 6.21 of Ref. [1] the presented distribution package includes KKMC version 4.16d compatible with Ref. [1] and several versions of the DIZET library: •[1.] Version 6.21 with updated input parameters, directory dizet-6.21. A thorough verification of the implementation DIZET 6.21 into KKMC was performed in Ref. [11].•[2.] Version 6.42 [12] used at the time when final LEP data was analyzed, directory dizet-6.42-cpc. This code was published with the version of hadronic contribution to virtual photon vacuum polarization [13], obsolete already at that publication time. However, its importance is that it is the last published version of the code and could be useful to reproduce some old published benchmarks [1,11].•[3.] Version 6.42 with the updated vacuum polarization of Ref. [14], directory dizet-6.42.•[4.] Version 6.45 of Ref. [15], directory dizet-6.45. It should be stressed that each variant of the DIZET library includes a specific variant for the dizet-xxx/input.data file, which redefines a few default input parameters defined in the .KK2f_defaults file.22In case of the use of predefined EW lookup tables, these redefinitions have to be repeated one more time in the user input file of KKMC used for the Monte Carlo generation run. Version specific parameters in the .KK2f_defaults of KKMC are for version 6.21, but constants like masses the of Z boson, Higgs boson and top quark, masses of other fermions and the QCD coupling constant are already updated to the present PDG values.33The original version is kept for the record as .KK2f_defaults-2000.At the lower energies, e.g. those of Belle-II it is required that the EW calculations are replaced by the fine tuned prediction for the photon vacuum polarization. Related issues are covered in the work of Ref. [16], being the most up to date version of the public archivization. It is not integrated into presented upgrade, as this is mainly targeting the needs of future high energy projects, while Belle-II is an on-going project.Nature of problem: Spin polarization of the τ in the process e+e−→τ+τ−(nγ),τ±→X± is used as an important data point for precise tests of the standard electroweak theory. The effects due to QED bremsstrahlung and apparatus efficiency have to be subtracted from the data. The program applies, as well, to the muon and neutrino pair production processes. It can simulate also the electron positron annihilation into u, d, s, c, b quark pairs. An important segment of the calculations rely on electroweak loop effects provided by the appropriate program library.Solution method: The Monte Carlo simulation of the combined τ production and decay process is used to calculate the spin effects and effects of radiative corrections, including hard bremsstrahlung, simultaneously. Any experimental cut and apparatus efficiency may easily be introduced by rejecting some of the generated events. Electroweak effects are provided with an external library with the help of disk stored lookup tables.Additional comments including restrictions and unusual features: The high precision of the program is assured in the region near the Z resonance. For other energy ranges it varies. At low energies predictions from electroweak libraries need to be replaced with an appropriate dedicated code.We document variants of electroweak libraries introduced over the years since KKMC was published [1] leaving other changes to further publications. The distribution package provided now corresponds to KKMC version 4.16 and its physics content is documented in Ref. [3]. Details other than the electroweak details of this version are not addressed, they do not differ from those of Ref. [1]. See also README.pdf file in the distribution directory for instruction how to install and run the present version. Note that the SANC project [17,18] is now the vigorous continuation of the DIZET and ZFITTER project.AcknowledgmentsWe acknowledge work of E. Richter-Was which was important for the completion of the present work. We would like to thank all authors of libraries used in the program for their cooperation and support, especially the authors of DIZET. This work is partly supported by two Polish National Science Center grants: 2016/23/B/ST2/03927 and DEC-2017/27/B/ST2/01391. Partial support of the CERN FCC Design Study Programme, USA is acknowledged. A. Arbuzov is grateful for support to the RFBR, Russia grant 20-02-00441.