TAUOLA of tau lepton decays—framework for hadronic currents, matrix elements and anomalous decays
This paper presents an update of the Monte Carlo event generator TAUOLA for tau lepton decays, with substantially increased list of decay channels and new initialization options. The core of the program is still written in FORTRAN, but necessary arrangements have been made to allow handling of the user-provided hadronic currents and matrix elements at the execution time. Such a solution allows for simple preparation of new hadronic currents. In addition the solution is useful for fitting to experimental data. By default, TAUOLA features a set of hadronic currents which are compatible with the default initialization used by the BaBar collaboration. Options for currents available in previous releases are available through internal flags. The new version of the program also includes an implementation of Lepton Flavor Violating tau decays. We present, as an example, a set of C++ methods for handling user-provided currents, matrix elements or new decay channels initialization. Documentation is not only for the physicists involved in analysis of high-statistics tau decay samples, but also for future contributors, preparing new hadronic current parameterizations with different model assumptions and arrangements facilitating fits and estimates of their uncertainties. The program is now ready for migration from FORTRAN to a different programming language. Already now, it cannot be expected that user is fluent in FORTRAN. For such users, certain aspects of the project required particularly detailed documentation.