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User-friendly extensions of KKMCee output and applications

Status of the work, as of \(27^{th}\) September 2025, by Ananya and Jim (advices from ZW too).

New attributes have been added to the HepMC3 output of KKMCee to make the spin information of the τ system easy to use. These are

  • (1) helicity like attributes
  • (2) tau decay polarimetric vectors
  • (3) spin weights (primarily for tests on ambiguities of helicity like attributes).

All this is to enable fits of SM parameters or new physics effects through weight calculations, also to facilitating new-physics studies. The newly added attributes enables fast validation of the spin modeling and (ambiguities behind) and the helicity-only approximation directly in user analyses, without re-running the generator and timely detector response. For validation, effort has been made to reproduce and extend the work of Korchin et. al. and also some plots from old ALEPH paper on fitting of Z boson couplings.

What we document

  • Physics details of the implemented quantities (definitions, frames, and conventions).
  • Examples of applications: fast reweighting with a stand alone code and systematic variations.
  • Ambiguities in weight calculations, which are being examined and documented.
  • A detailed description of this work is available in the paper Ananya et. al.

What is documented

  • Published version of KKMCee is Computer Physics Communications 283(2023) 108556
  • Algorithm described here require version 5.01.00 which is not yet (September \(27^{th}\) 2025) available from the distribution github.
  • KKMCee, some code versions, are at present available from github
  • At present (27 Sep 2025), to run explained here applications, the files TauPair.cxx , TauPair.h and KKceex.cxx have to be updated manually.
  • Some of the applications are documented already with papers on KORALZ and ALEPH papers. See also our paper Ananya et. al..

Contact

  • Ananya - ananya.tapadar@ifj.edu.pl
  • Jim - jim.john@ifj.edu.pl