PHOTOS as a pocket parton shower: flexibility tests for the algorithm

In this note we will recall the main tests that document robustness and flexibility of the PHOTOS design. This aspect may be of broader use and may find extensions in future applications, also outside the simple case of purely QED bremsstrahlung in decays. The components of the PHOTOS algorithm will...

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Autores principales: Golonka, Piotr, Was, Zbigniew
Lenguaje:eng
Publicado: CERN 2005
Materias:
Particle Physics - Phenomenology
Acceso en línea:http://cds.cern.ch/record/865014
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author Golonka, Piotr
Was, Zbigniew
author_facet Golonka, Piotr
Was, Zbigniew
author_sort Golonka, Piotr
collection CERN
description In this note we will recall the main tests that document robustness and flexibility of the PHOTOS design. This aspect may be of broader use and may find extensions in future applications, also outside the simple case of purely QED bremsstrahlung in decays. The components of the PHOTOS algorithm will be presented using operator language. The results of some flexibility tests, not documented before, will also be presented.
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institution Organización Europea para la Investigación Nuclear
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spelling cern-8650142023-09-15T02:06:42Zhttp://cds.cern.ch/record/865014engGolonka, PiotrWas, ZbigniewPHOTOS as a pocket parton shower: flexibility tests for the algorithmParticle Physics - PhenomenologyIn this note we will recall the main tests that document robustness and flexibility of the PHOTOS design. This aspect may be of broader use and may find extensions in future applications, also outside the simple case of purely QED bremsstrahlung in decays. The components of the PHOTOS algorithm will be presented using operator language. The results of some flexibility tests, not documented before, will also be presented.In this note we will recall the main tests that document robustness and flexibility of the PHOTOS design. This aspect may be of broader use and may find extensions in future applications, also outside the simple case of purely QED bremsstrahlung in decays. The components of the PHOTOS algorithm will be presented using operator language. The results of some flexibility tests, not documented before, will also be presented.In this note we will recall the main tests that document robustness and flexibility of the PHOTOS design. This aspect may be of broader use and may find extensions in future applications, also outside the simple case of purely QED bremsstrahlung in decays. The components of the PHOTOS algorithm will be presented using operator language. The results of some flexibility tests, not documented before, will also be presented.PHOTOS is widely used for generation of bremsstrahlung in decays of particlesand resonances in LHC applications. We document here its recent tests andvariants. Special emphasis is on those aspects which may be useful for newapplications in QED or QCD. Recently version 2.14 of the PHOTOS Monte Carloalgorithm, written for bremsstrahlung generation in decays became available. InRef. [1] detailed instructions on how to use the program are given. With respectto older versions [2,3] of PHOTOS, it now features: improved implementation ofQED interference and multiple-photon radiation. The numerical stability of thecode was significantly improved as well. Thanks to these changes, PHOTOSgenerates bremsstrahlung corrections in Z and W decays with a precision of 0.1%.This precision was established in [4] with the help of a multitude ofdistributions and of a specially designed numerical test (SDP), see Ref. [1],section 5 for the definition. The tests for other channels, such as semileptonicK decays and leptonic decays of the Higgs boson and the τ-lepton, are presentedin [4] as well. In those cases the level of theoretical sophistication for thereference distribution was lower though. In this note we will not repeat adiscussion of the design properties, but we will recall the main tests thatdocument robustness and flexibility of the PHOTOS design. The results of thecomparisons of PHOTOS running with different options of separation of itsphysical content into functional parts of the algorithm will be shown. Thedesign of the program, i.e. the relation between the parts of the algorithmremained unchanged for these tests. This aspect may be of broader use and mayfind extensions in future applications, also outside the simple case of purelyQED bremsstrahlung in decays. In the calculations that led to the constructionof PHOTOS we had to deal with the diagrams generated by photon couplings to thecharged fermions, scalars or vectors. They were definitely simpler than the onesrequired for the QCD, nonetheless they offered a place to develop solutionswhich may be of some use there as well. Having such possibility in mind, yet nothaving any extension to QCD at hand, we have called PHOTOS a pocket partonshower. We hope that the methods we developed would be useful for QCD at leastas pedagogical examples. We begin with a presentation of the components of thePHOTOS algorithm using operator language. The consecutive approximations used inthe construction of the crude distribution for photon generation, and thecorrecting weights used to construct the physically complete distributions arelisted, but can not be defined in detail here. Instead, we present thevariations of the algorithm. Comparisons between different options of thealgorithm provide an important class of technical tests, and also help toexplore the limits of the universality of the PHOTOS solution. The results ofsome of these tests will be listed later in the contribution (for the remainingones and the details we address the reader to refs. [1, 4]). In the comparisonswe use the SDP universal test based on MC-TESTER [5] as in Ref. [1]. We skip itsdefinition here as well. The starting point for the development of PHOTOS wasthe observation that, at first order, the bremsstrahlung corrections in the Z →µ + µ − process can be written as a convolution of the Born-level distributionwith the single-photon emission kernels for the emission from µ + and µ −. *Supported in part by the EU grant MTKD-CT-2004-510126, in partnership with theCERN Physics Department, and the Polish State Committee for Scientific Research(KBN) grant 2 P03B 091 27 for the years 2004–2006.CERNhep-ph/0508015IFJPAN-V-2005-8CERN-PH-TH-2005-139CERN-PH-TH-2005-139IFJPAN-V-2005-08oai:cds.cern.ch:8650142005-08-01
spellingShingle Particle Physics - Phenomenology
Golonka, Piotr
Was, Zbigniew
PHOTOS as a pocket parton shower: flexibility tests for the algorithm
title PHOTOS as a pocket parton shower: flexibility tests for the algorithm
title_full PHOTOS as a pocket parton shower: flexibility tests for the algorithm
title_fullStr PHOTOS as a pocket parton shower: flexibility tests for the algorithm
title_full_unstemmed PHOTOS as a pocket parton shower: flexibility tests for the algorithm
title_short PHOTOS as a pocket parton shower: flexibility tests for the algorithm
title_sort photos as a pocket parton shower: flexibility tests for the algorithm
topic Particle Physics - Phenomenology
url http://cds.cern.ch/record/865014
work_keys_str_mv AT golonkapiotr photosasapocketpartonshowerflexibilitytestsforthealgorithm
AT waszbigniew photosasapocketpartonshowerflexibilitytestsforthealgorithm

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