TAUOLA of τ lepton decays—framework for hadronic currents, matrix elements and anomalous decays

Abstract This paper presents an update of the Monte Carlo event generator TAUOLA for τ 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 τ 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 τ 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. Program summary Program Title: tauola-bbb Program Files doi: http://dx.doi.org/10.17632/7jx9ysfy7c.1 Licensing provisions: GPLv2 Programming language: FORTRAN/C++ Supplementary material: TAR BALL with benchmark results Journal reference of previous version: Comp. Phys. Comm., 183 (2012) 821–843 Does the new version supersede the previous version?: No Reasons for the new version: Meeting the needs of present day experiments. Nature of problem: Present day experiments have the capability to measure extremely rare, not yet measured τ decays, as well as precise measurements of known decay channels. They require a Monte Carlo generator capable of generating all desired decays. They also need the possibility to modify and test new models for such decays. At the same time the default initialization of the MC generator should contain decent modeling of known τ decays. Solution method: The new version is a continuation of [1, 2] and TAUOLA [3]. It has an extended decay channel list with methods for modification. An initialization equivalent to heritage BaBar one is provided. A framework for adding/replacing hadronic currents/matrix elements with a user-defined function has been introduced. Additional comments including Restrictions and Unusual features: A mixed-language environment is used, where interfacing and initialization data are placed in C++ structs, which can be accessed as F77 common blocks. The program is ready for full migration to C . TAR BALL of the program is available from: http://annapurna.ifj.edu.pl/~jzaremba/resources/tauola-bbb.html and also from: http://wasm.web.cern.ch/wasm/f77.html [1] Z. Was and P. Golonka. Nucl. Phys. Proc. Suppl, 144:88–94, 2005. [, 88(2004)]. [2] P. Golonka and B. Kersevan and T. Pierzchala and E. Richter-Waas and Z. Was and M. Worek Comput. Phys. Commun., 174:818-835, 2006. [3] S. Jadach, Z. Was, R. Decker, and Johann H. Kuhn. Comput. Phys. Commun., 76:361–380, 1993.