Status of new hadronic currents for tau lepton decay Monte Carlo generator
TAUOLA was revieved in other talks of the conference. Efforts on comparison
with BaBar and Belle collaboration data were carefully discussed. Also use of
the program in phenomenology of W decays measured by ATLAS collaboration was
presented in these talks as well. That is why, in my talk, I will concentrate
on other aspects of our work necessary for development of tau lepton Monte
Carlo programs and their phenomenological use.
  Presented results illustrate the status of the projects performed in
collaboration with Swagato Banerjee, Zofia Czyczula, Nadia Davidson, Jan
Kalinowski, Wojciech Kotlarski Tomasz Przedzinski, Olga Shekhovtsova, Elzbieta
Richter-Was, Pablo Roig, Jakub Zaremba, Qingjun Xu and others.Comment: 4 pages, Presented at International workshop on Tau Lepton Physics,
  TAU12 Nagoya, Japan, September, 201

Was, Z.

English

arXiv

Status of new hadronic currents for tau lepton decay Monte Carlo generator TAUOLA was revieved in other talks of the conference. Efforts on comparison with BaBar and Belle collaboration data were carefully discussed. Also use of the program in phenomenology of W decays measured by ATLAS collaboration was presented in these talks as well. That is why, in my talk, I will concentrate on other aspects of our work necessary for development of tau lepton Monte Carlo programs and their phenomenological use. Presented results illustrate the status of the projects performed in collaboration with Swagato Banerjee, Zofia Czyczula, Nadia Davidson, Jan Kalinowski, Wojciech Kotlarski Tomasz Przedzinski, Olga Shekhovtsova, Elzbieta Richter-Was, Pablo Roig, Jakub Zaremba, Qingjun Xu and others

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IFJPAN-IV-2012-15Status of TAUOLA and relatedprojectsZ. Wa¸sa,ba Institute of Nuclear Physics, PAN, Krako´w, ul. Radzikowskiego 152, Polandb CERN PH-TH, CH-1211 Geneva 23, Switzerland.ABSTRACTStatus of new hadronic currents for τ lepton decay Monte Carlo generator TAUOLA wasrevieved in other talks of the conference. Efforts on comparison with BaBar and Bellecollaboration data were carefully discussed. Also use of the program in phenomenology ofW decays measured by ATLAS collaboration was presented in these talks as well.That is why, in my talk, I will concentrate on other aspects of our work necessary fordevelopment of τ lepton Monte Carlo programs and their phenomenological use.Presented results illustrate the status of the projects performed in collaboration withSwagato Banerjee, Zofia Czyczula, Nadia Davidson, Jan Kalinowski, Wojciech KotlarskiTomasz Przedzin´ski, Olga Shekhovtsova, Elz˙bieta Richter-Wa¸s, Pablo Roig, Jakub Zaremba,Qingjun Xu and others.Presented at International Workshop on Tau Lepton Physics,TAU12 Nagoya, Japan, September, 2012IFJPAN-IV-2012-15December, 2012arXiv:1212.5556v1  [hep-ph]  21 Dec 20121 IntroductionThe TAUOLA package [1, 2, 3, 4] for simulation of τ -lepton decays and PHOTOS [5, 6, 7] forsimulation of QED radiative corrections in decays, are computing projects with a ratherlong history. Written and maintained by well-defined (main) authors, they nonethelessmigrated into a wide range of applications where they became ingredients of complicatedsimulation chains. As a consequence, a large number of different versions are presently inuse. Those modifications, especially in case of TAUOLA, are valuable from the physics pointof view, even though they often did not find the place in the distributed versions of theprogram. From the algorithmic point of view, versions may differ only in details, but theyincorporate many specific results from distinct τ -lepton measurements or phenomenologicalprojects. Such versions were mainly maintained (and will remain so) by the experimentstaking precision data on τ leptons. Interesting from the physics point of view changesare still developed in FORTRAN. That is why, for convenience of such partners, part of theTAUOLA should remain in FORTRAN for a few forthcoming years.Many new applications were developed in C++, often requiring a program interface toother packages (e.g., generating events for LHC, LC, Belle or BaBar physics processes).For the manipulation of matrix element, techniques of re-weighting events were furtherdeveloped. This required attention on numerical stability issues.The program structure did not change significantly since previous τ conference [8]. Letus concentrate on physics extentions and novel applications. We will only mention work onnew hadronic currents based on the Resonance Chiral approach. This topic was covered inother talks of the conference [9, 11, 10]. Important results are already obtained, but suffi-ciently good agreement with the experimental data is not yet achieved. New currents arenot integrated into main distribution tar-balls for FORTRAN and C++ applications. Furtherwork is on-going, weighted event techniques useful for fits are used. Analyses of high preci-sion, high-statistics data from Belle and BaBar are expected to profit from these solutions.Other aspects of the project such as interfaces for applications based on HepMC [12] eventrecord or new tests and weighting algorithms for spin effects in production processes shouldbe mentioned as well. In this context numerical stability of solutions used in re-weightingevents stored in datafiles is of importance.Our presentation is organized as follows: Section 2 is devoted to the discussion ofoptional weights in TAUOLA and their use for fits to experimental data. In section 3 we con-centrate on PHOTOS Monte Carlo for radiative corrections in decays. Section 4 is devoted tonew interfaces of TAUOLA and PHOTOS based on HepMC and written in C++. Work on inter-face to genuine weak corrections, transverse spin effects and new tests and implementationbremsstrahlung kernels will be presented as well. Comments on changes in MC-TESTER; theprogram designed for semi-automatic comparisons of simulation samples originating fromdifferent programs and heavily used in our projects are also given. Section 5 Summarycloses the talk.Because of the limited space of the contribution, some results will not be presented inthe proceedings. They find their place in publications, prepared with coauthors listed inthe Abstract. For these works, the present paper may serve as an advertisement.12 Approach of Resonance Chiral lagrangians and TAUOLAMonte CarloIn other talks [9, 11, 10] of the conference, Resonance Chiral Lagrangian approach wasused for calculations of new hadronic currents to be installed TAUOLA. That is why, we donot need to repeat its description here. In Ref. [13] implementation of those currents isdocumented in a great detail.Physics of τ lepton decays requires sophisticated strategies for the confrontation of phe-nomenological models with experimental data. On one hand, high-statistics experimentalsamples are collected, and the obtained precision is high, on the other hand, there is asignificant cross-contamination between distinct τ decay channels. Starting from a certainprecision level all channels need to be analyzed simultaneously. Change of parameteriza-tion for one channel contributing to the background to another one may be important forthe fit of its currents. This situation leads to a complex configuration where a multitudeof parameters (and models) needs to be simultaneously confronted with a multitude ofobservables. One has to keep in mind that the models used to obtain distributions in thefits may require refinements or even substantial rebuilds as a consequence of comparisonwith the data. The topic was covered in detail in the τ Section of Ref. [14]. At present ourcomparison with the data still do not require such refined methods.We enable calculation for each generated event (separately for decay of τ+ and/or τ−)alternative weights; the ratios of the matrix element squared obtained with new currents,and the one actually used in generation. Then, the vector of weights can be obtained andused in fits. We have checked that such a solution not only can be easily installed intoTAUOLA as a stand-alone generator, but it can also be incorporated into the simulationframeworks of Belle and BaBar collaborations. The weights can be calculated after thesimulation of detector response is completed. Only then choice of parameters for thehadronic currents has to be performed and the fits completed. This idea was also behindTauSpinner for LHC applications, described in Section 4.3 PHOTOS Monte Carlo for bremsstrahlung and its sys-tematic uncertaintiesThanks to exponentiation properties and factorization, the bulk of the final state QEDbremsstrahlung can be described in a universal way. However, the kinematic configura-tions caused by QED bremsstrahlung are affecting in an important way signal/backgroundseparation. It may affect selection criteria and background contaminations in quite complexand unexpected ways. In many applications, not only in τ decays, such bremsstrahlungcorrections are generated with the help of the PHOTOS Monte Carlo. That is why it is ofimportance to review the precision of this program as documented in Refs. [5, 6, 7]. Forthe C++ applications, the version of the program is available now. It is documented inRef. [15].2In C++ applications, the complete first-order matrix elements for the two-body decaysof the Z [16] and W [17] decays into a lepton pair are now available. Kernels with completematrix elements, for the decays of scalar B mesons into a pair of scalars [18] are availablefor the C++ users as well. For K → lνpi and for γ∗ → pi+pi− decays [17, 19] matrix elementbased kernels are still available for tests only. Properly oriented reference frames are neededin those cases. It will be rather easy to integrate those NLO kernels into the main version ofthe program, because of better control of the decay particle rest frame than in the FORTRANinterface.In all of these cases the universal kernel of PHOTOS is replaced with the one matching anexact first-order matrix element. In this way terms necessary for the NLO/NLL precisionlevel are implemented1. A discussion relevant for control of program systematic uncertaintyin τ → piν decay can be found in Ref. [21].The algorithm covers the full multiphoton phase-space and becomes exact in the softlimit. This is rather unusual for NLL compatible algorithms. One should not forgetthat PHOTOS generates weight-one events, and does not exploit any phase space ordering.There is a full phase space overlap between the one where a hard matrix element is usedand the one for iterated photon emission. All interference effects (between consecutiveemissions and emissions from distinct charged lines) are implemented with the help ofinternal weights.The results of all tests of PHOTOS with a NLO kernel confirm sub-permille precisionlevel. This is very encouraging, and points to the possible extension of the approachoutside of QED (scalar QED). In particular, to the domain of QCD or to QED whenphenomenological form factors for interactions of photons need to be used. For that workto be completed, spin amplitudes need to be studied. Let us point to Ref. [22] as anexample.New tests of PHOTOS are available from Ref. [23]. In those tests, in particular, resultsfrom the second-order matrix element calculations embedded in KKMC [31] Monte Carloare used in case of Z decay. For W decays comparisons with electroweak calculations ofRefs. [24, 25] are shown.4 TAUOLA universal interface and PHOTOS interface inC++In the development of packages such as TAUOLA or PHOTOS, questions of tests and ap-propriate relations to users’ applications are essential for their usefulness. In fact, userapplications may be much larger in size and human efforts than the programs discussedhere. Good example of such ‘user applications’ are complete environments to simulate1Note that here the LL (NLL) denotes collinear logarithms (or in case of differential predictions termsintegrating into such logarithms). The logarithms of soft singularities are taken into account to all orders.This is resulting from mechanisms of exclusive exponentiation [20] of QED. The algorithm used in PHOTOSMonte Carlo is compatible with exclusive exponentiation. Note that our LL/NLL precision level wouldeven read as respectively NLL/NNNLL level in some naming conventions of QCD.3MC-TESTEREvent Record(HepMC 2.03, 2.05, 2.06)(HEPEVT)PYTHIA 8Tauola C++InterfaceTAUOLAFORTRAN ROOTSANCmodulePhotos C++InterfacePHOTOSFORTRANTauSpinnerAlgebraicManipulationFigure 1: Scheme of Monte Carlo simulation system with communication based on event record.Each segment feature contribution from different people, may be coded in distinct programinnglanguage and/or be developped with the help of algebraic manipulation systems.physics process and control detector response at the same time. Distributions of final stateparticles are not always of direct interest. Often properties of intermediate states, such asa spin state of τ -lepton, coupling constants or masses of intermediate heavy particles areof prime interest. As a consequence, it is useful that such intermediate state properties areunder direct control of the experimental user and can be manipulated to understand detec-tor responses. Our programs worked well with FORTRAN applications where HEPEVT eventrecord is used. For the C++ HepMC [12] case, interfaces were rewritten, both for TAUOLA [26]and for PHOTOS [15]. The interfaces and as a consequence the programs themselves wereenriched; for PHOTOS new Matrix element kernels are available; for TAUOLA interface, a com-plete (not longitudinal only) spin correlations are available for Z/γ∗ decay. Electroweakcorrections taken from Refs. [24, 25] are also used. For the scheme of programs communi-cations see Fig. 1. In this spirit an algorithm of TauSpinner [27] to study detector responseto spin effects in Z,W and H decays, was developed. Recently TauSpinner was enriched[28] with the option to study effects of New Physics, such as effects of spin-2 states in τ+τ−pairs produced at LHC. Modular organization opens ways for further efficient algorithmsto understand detector systematics, but at the same time responsibility to control softwareprecision must be shared by the user. Automated tests of MC-TESTER were prepared [29].New functionalities were introduced into the testing package [30]. In particular, it worksnow with the HepMC event record, the standard of C++ programs, spectrum of availabletests is enriched and events stored on datafiles are easier to test.The program is available through the LHC Computing Grid (LCG) Project. See GENSERwebpage, Ref. [32], for details. This is the case for TAUOLA C++ and for PHOTOS C++ as well.The FORTRAN predecessors are available in this way too.45 Summary and future possibilitiesVersions of the hadronic currents available for the TAUOLA library until now, are all basedon old models and experimental data of 90’s. The implementation of new currents, basedon the Resonance Chiral Lagrangian approach is now prepared and tested from the tech-nical side. Methods for efficient confrontation with the experimental data are prepared aswell. Once comparison with Belle and BaBar data is successfully completed, new parame-terizations will be straightforward for use in a spectrum of applications in FORTRAN or C++environments.The status of associated projects: TAUOLA universal interface and MC-TESTER wasreviewed. Also the high-precision version of PHOTOS for radiative corrections in decays, waspresented. All these programs are available now for C++ applications thanks to the HepMCinterfaces.New results for PHOTOS were mentioned. For the leptonic Z and W decays the com-plete next-to-leading collinear logarithms effects can now be simulated in C++ applications.However, in most cases these effects are not important, leaving the standard version suffi-cient. Thanks to this work the path for fits to the data of electromagnetic form factors isopened [19], e.g. in the case of Kl3 decays.The presentation of the TAUOLA general-purpose interface in C++ was given. It is morerefined than the FORTRAN predecessor. Electroweak corrections can be used in calculation ofcomplete spin correlations in Z/γ∗ mediated processes. An algorithm for study of detectorresponses to spin effects in Z, W and H decays was shown.The present version of MC-TESTER is stable now. It works with C++ event record HepMCand enables user defined tests in experiments’ software environments. We used the toolregularly in our projects.6 AcknowledgementThis research was supported in part by the funds of Polish National Science Centre underdecision DEC-2012/04/M/ST2/00240 and DEC-2011/03/B/ST2/00107 and by the PolishGovernment grant NN202127937 (years 2009-2011).References[1] S. Jadach, J. H. Kuhn, and Z. Was, Comput. Phys. Commun. 64 (1990) 275.[2] M. Jezabek, Z. Was, S. Jadach, and J. H. Kuhn, Comput. Phys. Commun. 70 (1992)69.[3] S. Jadach, Z. Was, R. Decker, and J. H. Kuhn, Comput. Phys. Commun. 76 (1993)361–380.[4] P. Golonka et al., Comput. Phys. Commun. 174 (2006) 818–835, hep-ph/0312240.5[5] E. Barberio, B. van Eijk, and Z. Was, Comput. Phys. Commun. 66 (1991) 115.[6] E. Barberio and Z. Was, Comput. Phys. Commun. 79 (1994) 291–308.[7] P. Golonka and Z. Was, Eur. Phys. J. C45 (2006) 97–107, hep-ph/0506026.[8] Z. Was, Nucl. Phys. Proc. Suppl. 218, 249 (2011) [arXiv:1101.1652 [hep-ph]].[9] O. Shekhovtsova talk at International Workshop on Tau Lepton Physics, TAU12Nagoya, Japan, September, 2012.[10] I. Nugent talk at International Workshop on Tau Lepton Physics, TAU12 Nagoya,Japan, September, 2012.[11] P. Roig talk at International Workshop on Tau Lepton Physics, TAU12 Nagoya, Japan,September, 2012.[12] M. Dobbs and J. B. Hansen, Comput. Phys. Commun. 134 (2001) 41–46,https://savannah.cern.ch/projects/hepmc/.[13] O. Shekhovtsova, T. Przedzinski, P. Roig and Z. Was. “Resonance chiral Lagrangiancurrents and tau decay Monte Carlo,” 1203.3955 , Phys. Rev. D in print. alsohttp://annapurna.ifj.edu.pl/˜wasm/RChL/RChL.htm[14] S. Actis et al., Eur. Phys. J. C66 (2010) 585–686, 0912.0749.[15] N. Davidson, T. Przedzinski, and Z. Was, 1011.0937.[16] P. Golonka and Z. Was, Eur. Phys. J. C50 (2007) 53–62, hep-ph/0604232.[17] G. Nanava, Q. Xu, and Z. Was, Eur. Phys. J. C70 (2010) 673–688, 0906.4052.[18] G. Nanava and Z. Was, Eur. Phys. J. C51 (2007) 569–583, hep-ph/0607019.[19] Q. Xu and Z. Was, Eur. Phys. J. C 72, 2158 (2012) [arXiv:1201.0189 [hep-ph]].[20] S. Jadach, B. F. L. Ward, and Z. Was, Phys. Rev. D63 (2001) 113009,hep-ph/0006359.[21] Z. -H. Guo and P. Roig, Nucl. Phys. Proc. Suppl. 218, 122 (2011) [arXiv:1010.2838[hep-ph]].[22] A. van Hameren and Z. Was, 0802.2182.[23] P. Golonka, G. Nanava, and Z. Was, Tests of PHOTOS HardBremsstrahlung, http://mc-tester.web.cern.ch/MC-TESTER/PHOTOS-MCTESTER/ and A. Arbuzov, T. Przedzinski, R. Sadykov, Z. Washttp://annapurna.ifj.edu.pl/˜wasm/phNLO.htm, also A. Arbuzov, T. Przedzin-ski, R. Sadykov, Z. Was CERN-PH-TH/2012-3546[24] A. Andonov et al., 0812.4207.[25] A. Andonov et al., Comput. Phys. Commun. 174 (2006) 481–517, hep-ph/0411186.[26] N. Davidson, G. Nanava, T. Przedzinski, E. Richter-Was and Z. Was, Comput. Phys.Commun. 183, 821 (2012) [arXiv:1002.0543 [hep-ph]].[27] Z. Czyczula, T. Przedzinski and Z. Was, Eur. Phys. J. C 72, 1988 (2012)[arXiv:1201.0117 [hep-ph]].[28] S. Banerjee, J. Kalinowski, W. Kotlarski, T. Przedzinski and Z. Was, arXiv:1212.2873[hep-ph].[29] P. Golonka, T. Pierzchala, and Z. Was, Comput. Phys. Commun. 157 (2004) 39–62,hep-ph/0210252.[30] N. Davidson, P. Golonka, T. Przedzinski and Z. Was, Comput. Phys. Commun. 182,779 (2011) [arXiv:0812.3215 [hep-ph]].[31] S. Jadach, B. Ward, and Z. Was, Comput.Phys.Commun. 130 (2000) 260–325,hep-ph/9912214.[32] M. Kirsanov, A. Ribon, and O. Zenin, PoS ACAT08 (2008) 114.7

Status of TAUOLA and related projects

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