The Monte Carlo for lepton pair production and tau decays consist of KKMC for lepton pair production, tauola for tau lepton decays and photos for radiative corrections in decays. An effort for adaptation of the system for precision data to be collected at Belle II experiment lead to extension of phase space generation modules both in photos and tauola to enable decays and/or radiative corrections of additional light lepton pairs. The phase-space and matrix element parts of the programs are separated, that is why extension to processes where lepton pair is produced through narrow resonances, like dark photon, was straight forward. In the present version of tauola, list of tau decay channels is enriched with multitude of exotic ones, useful for searches of new physics. The hadronic currents parametrizations of main decay channels is prepared for basic simulation in the experiment. The basis for future work on precise fits of hadronic currents including Machine Learning is retained, but development of necessary software solutions is left for the forthcoming years. Presented programs versions are available in stand-alone format from gitlab or through the basf2 system of Belle II software. Official distribution web pages, documenting programs tests, are retained but not necessarily up to the date.

This dissertation focuses on the development process of scientific software. It presents a methodology that has emerged over time during development of Monte Carlo tools for high energy physics experiments. A short description of the physics background needed to understand the subjects presented in this dissertation is included and the different types of software created for the physics experiments are outlined. Challenges related to the scientific software development are presented. The development process of several projects is described. The development of subsequent milestones of these projects follow the cycle of improving the physics model, describing the model using mathematical formalism, implementing the model with numerical approximations, creating the software framework, documenting and validating results. The relation between increased precision of the results and increased complexity of tests and test frameworks is also demonstrated based on these projects. The subject of scientific software testing is addressed and the taxonomy of the scientific software tests is presented including testing techniques used in the development of this software. Author of this dissertation co-authored tools presented in it. Some of these tools have been introduced into the HEP community. Some gained large user base and are in active use by the community. Some of them are part of analyses performed by experiments around Large Hadron Collider. The analysis of the development process of these tools can help estimate the effort needed to improve the design and precision of complex algorithms.

We present the HepMC3 library designed to perform manipulations with event records of High Energy Physics Monte Carlo Event Generators (MCEGs). The library is a natural successor of HepMC and HepMC2 libraries used in the present and in the past. HepMC3 supports all functionality of previous versions and significantly extends them. In comparison to the previous versions, the default event record has been simplified, while an option to add arbitrary information to the event record has been implemented. Particles and vertices are stored separately in an ordered graph structure, reflecting the evolution of a physics event and enabling usage of sophisticated algorithms for event record analysis. The I/O functionality of the library has been extended to support common input and output formats of HEP MCEGs, including formats used in Fortran HEP MCEGs, formats used in HepMC2 library and ROOT. The functionality of the library allows the user to implement a customised input or output format. The library is already supported by popular modern MCEGs (e.g. Sherpa and Pythia8) and can replace the older HepMC versions in many others.

In the present paper we describe the set of form factors for hadronic τ decays based on Resonance Chiral Theory. The technical implementation of the form factors in FORTRAN code is also explained. It is shown how it can be installed into TAUOLA Monte Carlo program. Then it is rather easy to implement into software environments of not only Belle and BaBar collaborations but also for FORTRAN and C++ applications of LHC. The description of the current for each τ decay mode is complemented with technical numerical tests. The set is ready for fits, parameters to be used in fits are explained. Arrangements to work with the experimental data not requiring unfolding are prepared. Hadronic currents, ready for confrontation with the τ decay data, but not yet ready for the general use, cover more than 88 % of hadronic τ decay width. IFJPAN-IV-2011-6 UAB-FT/695 FTUV/2011-09-29 IFIC/11-53 CERN-PH-TH/2012-016 March, 2012

The Monte Carlo for lepton pair production andtau decays consist of KKMC for lepton pair production, tauola for tau lepton decays and photos for radiative corrections in decays. An effort for adaptation of the system for precision data being collected at the Belle II experiment included simulation of additional light lepton pairs. Extension to processes where lepton pair is produced through narrow resonances, like dark photon or dark scalar phi resonances, was straight forward. Modified programs versions are available in stand-alone format from gitlab repository or through the basf2 system of Belle II software. It was explained recently during the International Workshop on Tau Lepton Physics September, 2021, Bloomington IN. Now we concentrate on simulations for phi resonance, a hypothetical object which could be responsible for anomalous moment g-2 in Z-τ-τinteractions through virtual contributions.

$$\uptau $$ -leptons produced in pp collisions allow to measure Standard Model parameters and offer probes for New Physics. The TauSpinner program can be used to modify spin (or production matrix elements) effects in any $$\uptau $$ sample. It relies on the kinematics of outgoing particles: $$\uptau $$ lepton(s) (also $$\upnu _\uptau $$ in case of W-mediated processes, optionally also four-moments of accompanying hard jets) and $$\uptau $$ decay products. No other information is required from the event record. With calculated spin (or production/decay matrix element) weights, attributed on the event-by-event basis, modifications to the spin/decay/production features, is possible without the need for regenerating events. With TauSpinner algorithms, the experimental techniques developed over years since LEP 1 times are already used and extended for LHC applications. The purpose of the present publication is to systematically document physics basis of the program, and to overview its application domain and systematic errors.

We present 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 remains 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 solution may simplify preparation of new hadronic currents and may be useful for fitting to the experimental data as well. We have implemented as default for TAUOLA a set of hadronic currents, which is compatible with the default initialization used by BaBar collaboration. Options for currents available in previous releases are still stored in the code, sometimes left defunct or activated by internal flags only. The new version of the program, includes also implementation of Lepton Flavour Violating tau decays. Finally, we present, as an example, a set of C++ methods for handling user-provided currents, matrix elements or complete new decay channels initialization which can be performed at the program execution time.

For five years now, PHOTOS Monte Carlo for bremsstrahlung in the decay of particles and resonances has been available with an interface to the C++ HepMC event record. The main purpose of the present paper is to document the technical aspects of the PHOTOS Monte Carlo installation and present version use. A multitude of test results and examples are distributed together with the program code. The PHOTOS C++ physics precision is better than its FORTRAN predecessor and more convenient steering options are also available. An algorithm for the event record interface necessary for process dependent photon emission kernel is implemented. It is used in Z and W decays for kernels of complete first order matrix elements of the decays. Additional emission of final state lepton pairs is also available. Physics assumptions used in the program and properties of the solution are reviewed. In particular, it is explained how the second order matrix elements were used in design and validation of the program iteration procedure. Also, it is explained that the phase space parametrization used in the program is exact.

For five years now, PHOTOS Monte Carlo for bremsstrahlung in the decay of particles and resonances has been available with an interface to the C++ HepMC event record. The main purpose of the present paper is to document the technical aspects of the PHOTOS Monte Carlo installation and present version use. A multitude of test results and examples are distributed together with the program code. The PHOTOS C++ physics precision is better than its FORTRAN predecessor and more convenient steering options are also available. An algorithm for the event record interface necessary for process dependent photon emission kernel is implemented. It is used in Z and W decays for kernels of complete first order matrix elements of the decays. Additional emission of final state lepton pairs is also available. Physics assumptions used in the program and properties of the solution are reviewed. In particular, it is explained how the second order matrix elements were used in design and validation of the program iteration procedure. Also, it is explained that the phase space parameterization used in the program is exact. Program title: Photos++ Catalogue identifier: AEYF_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEYF_v1_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 53720 No. of bytes in distributed program, including test data, etc.: 1297747 Distribution format: tar.gz Programming language: C++. Computer: PC. Operating system: Linux, MacOS. RAM: Bytes. Libraries take less than 2 MB. Memory complexity is O(n) with around 2–4 MB for events with 10 k particles. Classification: 11.1, 11.2. Nature of problem: Algorithm described in this paper can be used to add final state radiation to the event generated by external software using selected event record format. It can also be used on a sample of events loaded from data file. User can define parts of the decay tree on which algorithm can be invoked. The influence of the next-to-leading-order corrections, along with other options regarding electron–positron pair, muon pair and photon emission, can be studied. Solution method: The event record is traversed and a list of all decaying particles is created. Decays where program is not supposed to act and decays excluded by the user are removed from the list. The photon and pair adding algorithm is invoked separately on each remaining decay. If one or more particle is added to the decay, the kinematic of the whole decay tree is updated. Restrictions: Application of the algorithm strongly depends on the content on the event record. Insufficient precision or missing information may deteriorate quality of the results of the algorithm or prevent algorithm from working on the event or its parts. See Section 2 for more details. Running time: 10-30 s per 100k events for small events (less than 1k particles). The complexity strongly depends on the event content and user selection of excluded decays. The theoretical pessimistic complexity of the algorithm is O(n2). However, such cases are highly unrealistic. In our tests, the average complexity is around O(n1.2).

In this note we present a new parametrization of the hadronic current for the decay τ → πππvτ derived from the chiral lagrangian with explicit inclusion of resonances. We have included both scalar, vector and axial-vector resonances. For the first time, the lowest tensor resonance (f2(1270)) is included as well. Both single and double-resonance contributions to the hadronic form factors are taken into account. To satisfy the correct high energy behaviour of the hadronic form factors, constraints on numerical values of the vertex constants are obtained.

After developing a Resonance Chiral Lagrangian (RχL) model to describe hadronic τ lepton decays [18], the model was confronted with experimental data. This was accomplished using a fitting framework which was developed to take into account the complexity of the model and to ensure the numerical stability for the algorithms used in the fitting. Since the model used in the fit contained 15 parameters and there were only three 1-dimensional distributions available, we could expect multiple local minima or even whole regions of equal potential to appear. Our methods had to thoroughly explore the whole parameter space and ensure, as well as possible, that the result is a global minimum. This paper is focused on the technical aspects of the fitting strategy used. The first approach was based on re-weighting algorithm published in [17] and produced results in around two weeks. Later approach, with improved theoretical model and simple parallelization algorithm based on Inter-Process Communication (IPC) methods of UNIX system, reduced computation time down to 2-3 days. Additional approximations were introduced to the model decreasing time to obtain the preliminary results down to 8 hours. This allowed to better validate the results leading to a more robust analysis published in [12].

The tau-lepton plays an important role in the physics program at LHC. Its spin can be used for separation of signal from background or in measuring properties of New Particles decaying to tau leptons. The TauSpinner package represents a tool to modify tau spin effects in any sample containing tau leptons. Generated events, featuring taus produced from intermediate state W, Z, H bosons can be used as an input. The information on the polarization and spin correlations is reconstructed from the kinematics of the tau lepton(s) (nutau in case of W-mediated processes) and tau decay products. By weights, attributed on the event-by-event basis, it enables numerical evaluation and/or modification of the spin effects. We review distributions to monitor spin effects in leptonic and hadronic tau decays with up to three pions, to provide benchmarks for validation of spin content of the event sample and to visualize the tau lepton spin polarization and correlation effects. The demonstration examples for use of TauSpinner libraries, are documented. New validation methods of such an approach are provided. Other topics, like TauSpinner systematic errors or sensitivity of experimental distributions to spin, are addressed in part only. This approach is of interest for implementation of spin effects in embedded tau lepton samples, where Z to mu mu events from data of muons are replaced by simulated tau leptons. Embedding is used at LHC for estimating Z to tau tau background to H to tau tau signatures.

We present the results of a partial upgrade to the Monte Carlo event generator TAUOLA using Resonance Chiral Theory for the two and three meson final states. These modes account for 88% of total hadronic width of the tau meson. The first results of the model parameters have been obtained using Preliminary BaBar data for 3π mode.

In this paper, we discuss application of the TauSpinner package as a simulation tool for measuring the CP state of the newly discovered Higgs boson using the transverse spin correlations in the H →ττ decay channel. We discuss application for its main background Z/γ ^* →ττ as well. The TauSpinner package allows to add, with the help of weights, transverse spin correlations corresponding to any mixture of scalar/pseudoscalar state, on already existing events using information from the kinematics of outgoing τ leptons and their decay products only. This procedure can be used when polarimetric vectors of the τ s decays and density matrix for τ -pair production are not stored with the event sample. We concentrate on the well-defined effects for the Higgs (or Higgs-like scalar) decays, which are physically separated from the production processes. TauSpinner also allows to reintroduce (or remove) spin correlations to events from Drell–Yan Z/γ ^* →ττ process, the main background for the Higgs parity observables, again with the help of weights only. From the literature, we recall well-established observables, developed for measuring the CP of the Higgs, and use them as benchmarks for illustrating applications of the TauSpinner package. We also include a description of the code and prepared testing examples.

In this paper, we discuss application of the TauSpinner package as a simulation tool for measuring the CP state of the newly discovered Higgs boson using the transverse spin correlations in the \(H \rightarrow \tau \tau \) decay channel. We discuss application for its main background \(Z/\gamma ^* \rightarrow \tau \tau \) as well. The TauSpinner package allows to add, with the help of weights, transverse spin correlations corresponding to any mixture of scalar/pseudoscalar state, on already existing events using information from the kinematics of outgoing \(\tau \) leptons and their decay products only. This procedure can be used when polarimetric vectors of the \(\tau \)s decays and density matrix for \(\tau \)-pair production are not stored with the event sample. We concentrate on the well-defined effects for the Higgs (or Higgs-like scalar) decays, which are physically separated from the production processes. TauSpinner also allows to reintroduce (or remove) spin correlations to events from Drell–Yan \(Z/\gamma ^* \rightarrow \tau \tau \) process, the main background for the Higgs parity observables, again with the help of weights only. From the literature, we recall well-established observables, developed for measuring the CP of the Higgs, and use them as benchmarks for illustrating applications of the TauSpinner package. We also include a description of the code and prepared testing examples.

Evidence of a new particle with mass ~125 GeV decaying into a pair of tau leptons at the Large Hadron Collider spurs interest in ascertaining its spin in this channel. Here we present a comparative study between spin-0 and spin-2 nature of this new particle, using spin correlations and decay product directions. The TauSpinner algorithm is used to re-weight distributions from qqbar -> gamma/Z -> tau+ tau- sample to simulate a spin-2 state exchange. The method is based on supplementing the Standard Model matrix elements with those arising from presence of a new interaction. Studies with simulated samples demonstrate the discrimination power between these spin hypotheses based on data collected at the Large Hadron Collider.

In this paper we document the modifications introduced to the previous version of the resonance chiral Lagrangian current [Phys. Rev. D 86, 113008 (2012)] of the tau(-) ->pi(-)pi(-)pi(+)nu(tau) decay which enable the one-dimensional distributions measured by the BABAR Collaboration to be well modeled. The main change required to model the data is the addition of the sigma resonance. Systematic errors, theoretical and experimental ones, limitations due to fits of one-dimensional distributions only, and resulting difficulties and statistical/ systematic errors for fitted parameters are addressed. The current and fitting environment is ready for comparisons with the fully exclusive experimental data. The present result for tau(-) ->pi(-)pi(-)pi(+)nu(tau) is encouraging for work on other tau decay modes and resonance chiral Lagrangian based currents.

Final states involving tau leptons are important components of searches for new particles at the Large Hadron Collider (LHC). A proper treatment of tau spin effects in the Monte Carlo (MC) simulations is important for understanding the detector acceptance as well as for the measurements of tau polarization and tau spin correlations. In this note we present a TauSpinner package designed to simulate the spin effects. It relies on the availability of the four-momenta of the taus and their decay products in the analyzed data. The flavor and the four-momentum of the boson decaying to the τ−τ+ or τ±ν pair need to be known. In the Z/γ∗ case the initial state quark configuration is attributed from the intermediate boson kinematics, and the parton distribution functions (PDF’s). TauSpinner is the first algorithm suitable for emulation of tau spin effects in tau-embedded samples. It is also the first tool that offers the user the flexibility to simulate a desired spin effect at the analysis level. An algorithm to attribute tau helicity states to a previously generated sample is also provided. (Submitted to Eur. Phys. J. C ) 1Institute of Nuclear Physics, Cracow, Poland 2Institute of Physics, Jagiellonian University, Cracow, Poland 3CERN, CH-1211, Geneva 23, Switzerland, Theory Group, Physics Department 4Yale University, New Haven, USA *The work of Tomasz Przedzinski was supported in part by the Polish Government grant NN202127937 (years 2009-2011). 1 ar X iv :1 20 1. 01 17 v2 [ he pph ] 1 7 M ar 2 01 2

Evidence of a new particle with mass ∼125 GeV decaying into a pair of tau leptons at the Large Hadron Collider spurs interest in ascertaining its spin in this channel. Here we present a comparative study between spin-0 and spin-2 nature of this new particle, using spin correlations and decay product directions. The TauSpinner algorithm is used to re-weight distributions from q q̅→γ/Z →τ^+τ^- sample to simulate a spin-2 state exchange. The method is based on supplementing the Standard Model matrix elements with those arising from presence of a new interaction. Studies with simulated samples demonstrate the discrimination power between these spin hypotheses based on data collected at the Large Hadron Collider.