The Physics Analysis eXpert (PAX) is an open source toolkit for high energy
physics analysis. The C++ class collection provided by PAX is deployed in a
number of analyses with complex event topologies at Tevatron and LHC. In this
article, we summarize basic concepts and class structure of the PAX kernel. We
report about the most recent developments of the kernel and introduce two new
PAX accessories. The PaxFactory, that provides a class collection to facilitate
event hypothesis evolution, and VisualPax, a Graphical User Interface for PAX
objects

Erdmann, M.

Felzmann, U.

Flossdorf, A.

Kappler, S.

Kirsch, M.

Mueller, G.

Quast, G.

Saout, C.

Schmidt, A.

Weng, J.

English

arXiv

Kappler, Steffen

Erdmann, Martin

Kirsch, Matthias

Müller, G.

Floßdorf, A.

RWTH Publications

Concepts, developments and advanced applications of the PAX toolkit

The Physics Analysis eXpert (PAX) is an open source toolkit for high energy physics analysis. The C++ class collection provided by PAX is deployed in a number of analyses with complex event topologies at Tevatron and LHC. In this article, we summarize basic concepts and class structure of the PAX kernel. We report about the most recent developments of the kernel and introduce two new PAX accessories. The PaxFactory, that provides a class collection to facilitate event hypothesis evolution, and VisualPax, a Graphical User Interface for PAX objects.The Physics Analysis eXpert (PAX) is an open source toolkit for high energy physics analysis. The C++ class collection provided by PAX is deployed in a number of analyses with complex event topologies at Tevatron and LHC. In this article, we summarize basic concepts and class structure of the PAX kernel. We report about the most recent developments of the kernel and introduce two new PAX accessories. The PaxFactory, that provides a class collection to facilitate event hypothesis evolution, and VisualPax, a Graphical User Interface for PAX objects

Muller, G.

CERN Document Server

arXiv:physics/0605063 v1   7 May 2006Concepts, Developments and Advanced Applications of the PAX ToolkitS. Kappler∗, M. Erdmann, M. Kirsch, G. Mu¨ller (RWTH Aachen university, Germany),J. Weng (CERN, Geneva, Switzerland), A. Floßdorf (DESY, Hamburg, Germany),U. Felzmann, G. Quast, C. Saout, A. Schmidt (Karlsruhe university, Germany)AbstractThe Physics Analysis eXpert (PAX) is an open sourcetoolkit for high energy physics analysis. The C++ class col-lection provided by PAX is deployed in a number of analy-ses with complex event topologies at Tevatron and LHC. Inthis article, we summarize basic concepts and class struc-ture of the PAX kernel. We report about the most recentdevelopments of the kernel and introduce two new PAXaccessories. The PaxFactory, that provides a class collec-tion to facilitate event hypothesis evolution, and VisualPax,a Graphical User Interface for PAX objects.INTRODUCTIONPhysics analyses at modern collider experiments enter anew dimension of event complexity. At the LHC, for in-stance, physics events will consist of the final state prod-ucts of the order of 20 simultaneous collisions. In addition,a number of todays physics questions is studied in channelswith complex event topologies and configuration ambigui-ties occurring during event analysis.The Physics Analysis eXpert toolkit (PAX) is a continu-ously maintained and advanced C++ class collection, spe-cially designed to assist physicists in the analysis of com-plex scattering processes [1, 2, 3, 4]. PAX is realized inthe C++ programming language [5]. It provides additionalfunctionality in top of the vector algebra of the widely-spread libraries CLHEP [6] (default) or ROOT [7]. ThePAX container model as well as file I/O are based on theC++ Standard Template Library (STL) [5].THE PAX KERNELThe class collection of the PAX kernel allows the defi-nition of an abstraction layer beyond detector reconstruc-tion by providing a generalized, persistent HEP event con-tainer with three types of physics objects (particles, verticesand collisions), relation management and file I/O scheme.The PAX event container is capable of storing the com-plete information of multi-collision events (including de-cay trees with spatial vertex information, four-momenta aswell as additional reconstruction data). An automated copyfunctionality for the event container allows the analyst toconsistently duplicate event containers for hypothesis evo-lution, including its physics objects and relations. PAXphysics objects can hold pointers to an arbitrary number ofinstances of arbitrary C++ classes, allowing the analyst to∗Corresponding author: Steffen.Kappler@cern.chkeep track of the data origin within the detector reconstruc-tion software. Further advantages arising from the usageof the PAX toolkit are a unified data model and nomencla-ture, and therefore increased code lucidity and more effi-cient team work. The application of the generalized eventcontainer provides desirable side-effects, such as protectionof the physics analysis code from changes in the underly-ing software packages and avoidance of code duplicationby the possibility of applying the same analysis code tovarious levels of input data.PAX physics objectsThe three types of generalized physics objects providedby the PAX kernel are:• Particles (or reconstructed objects), i.e. Lorentz-vectors, are represented by the class PaxFourVector.• Vertices, i.e. three-vectors, represented by the classPaxVertex, are foreseen to realize particle decays.• Collisions, represented by the class PaxCollision, areforeseen to allow the separation of multiple interac-tions in high-luminostity environments.The vector characteristics of the classes PaxFourVector andPaxVertex is inherited from the corresponding classes ofthe CLHEP or ROOT libraries. Commonly needed, addi-tional properties such as a name, particle-id, status, charge,a workflag etc. can be stored in data members. Specificinformation complementary to data members, such as b-tags, jet cone sizes or energy corrections, for instance, canbe stored in the so-called user records (i.e. collections ofstring-double pairs).Each PAX physics object can record pointers to an ar-bitrary number of instances of arbitrary C++ classes. Thisway, the user can keep track of the data origin within thedetector reconstruction software, for instance. Access tothe pointers is possible at the same runtime during any laterstage of the analysis.Copy constructors are provided to perform deep copiesof PAX physics objects. When copying a PAX physics ob-ject, all pointers are copied as well. For the convenienceof reconstructing particle decay chains, PAX physics ob-jects are enabled to establish relations and can be organizedin containers based on the STL class templates map<key,item> and multimap<key, item>, respectively.Event containerPAX provides a generalized event container for storageand handling of the complete information of one multicolli-sion event including decay trees, spatial vertex information,four-momenta as well as additional reconstruction data inthe user records.This container is represented by the class PaxEventIn-terpret. This class is so named, because it is intended torepresent a distinct interpretation of an event configuration(e.g. connecting particles to the decay tree according toone out of a number of hypotheses, applying different jetenergy corrections, etc.). To facilitate the development ofnumerous parallel or subsequent event interpretations, thePaxEventInterpret class features a copy constructor, whichprovides a deep copy of the event container with all datamembers, physics objects, and their redirected relations.The PAX toolkit offers a file I/O scheme for persistentstorage of the event container, based on STL streams. Itallows the user to write the contents of PaxEventInterpretinstances with all contained physics objects as well as theirrelations to PAX data files. When restoring the data fromfile, an empty PaxEventInterpret instance is filled with thestored data and objects and all object relations are repro-duced.The PAX data file format is multi-version and multi-platform compatible and consists of binary data chunks,that allow file structure checks and fast positioning.PAX also provides the possibility to write/read Pax-EventInterpret instances to/from strings. This way, the usercan store PAX objects to any data format supporting stringsor binary data fields like databases or experiment specificdata formats.All classes of the PAX kernel can be used in compiledmode within the C-interpreter of ROOT. A more detaileddescription of the PAX kernel functionalities can be foundin reference [4].THE PAX ACCESSORIESThe PAX factoryThe PaxFactory is an accessory to the PAX kernel thatfacilitates the bookkeeping of event hypothesis evolution.The class PaxProcess is designed to allow the evolu-tion of different combinatorial hypotheses (event interpre-tations) of an event according to a certain physics process.This task arises during the a priori ambiguous partonic re-construction of processes with multiple reconstructed ob-jects of the same type. Figure 1 gives single top productionwith leptonic top decay for illustration: permuting the plot-ted three jets from figure 1.b at the t→Wb vertex in figure1.a provides three different hypotheses. In addition, thenormally two-fold ambiguity of the longitudinal neutrinomomentum, as provided by a W-mass constraint, doublesthe number of combinatorial hypothesis for the t-quark.With the PaxProcess class, the analyst can store and man-age an arbitrary number of event-interpretations includingtheir physics objects and relations. Like all other PAX ob-jects, a PaxProcess instance allows to store data in the userrecords and can record pointers to an arbitrary number ofinstances of arbitrary C++ classes.Figure 1: a) Schematic view of single top production withleptonic top decay. b) The visible reconstructed partons ofthis channel.A higher degree of automation at the evolution of com-binatorial hypotheses is provided by the class PaxAutoPro-cess. This derivative of the PaxProcess class features au-tomatic evolution of all possible combinatorial hypothesesof an event. The rules, according to which these hypothe-ses are evolved, are defined by user-defined static process-model, that is passed to the PaxAutoProcess instance atconstruction time. This process-model is a PaxEventInter-pret instance containing a prototype of the process decay-chain with parameters customizing the behaviour of thePaxAutoProcess class. The remaining step, to be done bythe analyst, is to further process the evolved event interpre-tations in standard decision techniques, for instance.Figure 2: Schematic view of a) single top production andits main backgrounds b) top-pair production and c) jet-associated W production.A further aspect of hypothesis evolution, besides the res-olution of combinatorial ambiguities, is the parallel evo-lution of different physics process hypotheses of an event.As illustrated in figure 2 for the analysis of single top pro-duction, the analyst might want to distinguish the signalchannel (figure 2.a) from its main backgrounds individu-ally (figure 2.b and 2.c).To allow easy management of different physics processhypotheses of an event, the The class PaxProcessFactoryprovides storage and easy access to an arbitrary number ofprocesses (i.e. instances of the class PaxProcess or deriva-tives) as well as user records and recording of arbitrary C++pointers.While the PaxEventInterpret instances with their physicsobjects are intented to remain in memory for one event, theclasses of the PaxFactory accessory are designed for life-times of up to one computing job. Therefore, the classesPaxProcess and PaxProcessFactory provide virtual mem-ber functions to be called at the beginning and end of a job,at the beginning and end of a run, and, of course, at eventanalysis and event finishing time. By default, the methodsof the PaxProcessFactory class invoke the correspondingmethods of all managed PaxProcess instances.The PaxFactory accessory provides the class Pax-EventInterpretTTree, which allows to automatically copyselected observables from PaxEventInterpret instances onan event-by-event basis into the TTree of a ROOT file.Those observables may be kinematic data or user records ofcertain contained physics objects as well as user-records ofthe event-interpretation. The automatic copy is performedaccording to a user-defined, static copy-model in the formof a PaxEventInterpret instance, that is passed to the Pax-EventInterpretTTree instance at construction time.Figure 3: The Graphical User-Interface of VisualPax al-lows browsing of PAX I/O files and editing of PaxEventIn-terpret instances.Visual PAXVisualPax is a recenlty developed accessory to the PAXkernel that allows browsing of PAX I/O files and editing ofPaxEventInterpret instances in a Graphical User-Interface.VisualPax is based on the wxWidgets open source, cross-platform native user-interface framework [8]. As shownFigure 4: Example scheme for the use of the PAX kernelplus accessories in advanced physics analyses. The samesoftware is used in different configurations when runningover a) experiment data and b) Monte-Carlo data.in figure 3, VisualPax allows to graphically display andmodify event interpretations including properties and de-cay chains of the contained physics objects. Therefore,with the help of VisualPax and PAX I/O files, the process-models for PaxAutoProcess instances as well as the copy-models for PaxEventInterpretTTree instances can be man-aged in a comfortable way.PAX ADVANCED ANALYSIS EXAMPLEAdvanced physics analyses realized with the PAX kerneland accessories can be designed according to the schemashown in figure 4.When running over experiment data, a dedicated,experiment-specific interface class for filling the PAX con-tainers (i.e. PaxEventInterpret instances) represents the in-terface between detector reconstruction software and thePAX factory. Once all relevant information is filled, the ob-jects are passed to a PaxProcessFactory instance that man-ages PaxAutoProcess instances for each of the physics pro-cesses under study. Each of the PaxAutoProcess instancesnow evolves the combinatorial hypotheses for each eventaccording to its process-model, that has been prepared ear-lier, e.g. with VisualPax. The virtual method finishEvent()of the PaxProcessFactory class then can be used to processthe resulting event hypotheses of all processes with deci-sion techniques such as Likelihood methods, Neural Net-works, Decision Trees etc. The results of the analysis canbe written to PAX I/O files or selected observables can bewritten to a TTree of a ROOT file by using the PaxEventIn-terpretTTree class.When running over Monte-Carlo data, the generator in-formation can be passed to the PAX factory in addition.Furthermore, the PaxProcessFactory can be extended byPaxProcess derivatives exploiting the Monte-Carlo truth inorder to train the deployed decision techniques in terms ofambiguity resolution and background-process suppression.VisualPax can be used at any stage of the analysis to re-define process-models or monitor the results.PAX PROJECT INFRASTRUCTUREThe PAX kernel and its officially supported accessoriesare continuously maintained and further developed by cur-rently eight core developers and undergoes regular qualityensurance [9]. The PAX webpage [10] provides the PAXUsers Guide [11], a comprehensive text documentation ofthe PAX toolkit, as well as class reference and fast naviga-tor pages for download or online use. Version managementof the software project is handled with a web-browsableVersion Control System (CVS) [12][13].ACKNOWLEDGEMENTSThe authors would like to thank Dominic Hirschbuehl,Yves Kemp, Patrick Schemitz, and Thorsten Walter, forhelpful contributions and feedback.REFERENCES[1] M. Erdmann et al., Physics Analysis Expert, Proceedings ofthe 14th Topical Conference on Hadron Collider Physics,HCP2002, Karlsruhe, Germany, 2002.[2] M. Erdmann, D. Hirschbu¨hl, C. Jung, S. Kappler, Y. Kemp,M. Kirsch et al., Physics Analysis Expert PAX: First Ap-plications, Proceedings of the conference on Computingin High Energy and Nuclear Physics (CHEP03), La Jolla,USA, physics/0306085, 2003.[3] M. Erdmann, U. Felzmann, D. Hirschbu¨hl, C. Jung, S. Kap-pler, M. Kirsch et al., New Applications of PAX in PhysicsAnalyses at Hadron Colliders, Proceedings of the confer-ence on Computing in High Energy and Nuclear Physics(CHEP04), Interlaken, Switzerland, 2004.[4] S. Kappler, M. Erdmann, U. Felzmann, D. Hirschbu¨hl,M. Kirsch, G. Quast et al., The PAX Toolkit and its Appli-cations at Tevatron and LHC, IEEE Trans. Nucl. Sci., vol.53, no. 2, 2006.[5] B. Stroustrup, The C++ Programming Language, AddisonWesley, ISBN 0-201-88954-2, 1997.[6] CLHEP library, documentation online available:http://proj-clhep.web.cern.ch/proj-clhep/, 2006.[7] R. Brun et al., ROOT, an object oriented data analysisframework, Proceedings of the 23rd CERN School of Com-puting, Marathon (Greece), 2000.[8] wxWidgets: open source, cross-platform native UI frame-work, online available: http://www.wxwidgets.org/, 2004-2006.[9] Borland Together Architect, Borland Software Corporation,20450 Stevens Creek Blvd., Cupertino, CA 95014, USA,2005.[10] M. Erdmann, S. Kappler, M. Kirsch, A. Schmidt, PAX –Physics Analysis eXpert, online documentation and support:http://cern.ch/pax, 2006.[11] M. Erdmann, S. Kappler, M. Kirsch, A. Schmidt, PAX UsersGuide, online available: http://cern.ch/pax, 2006.[12] CVS - Concurrent Version System, documentation onlineavailable: http://www.nongnu.org/cvs/, 2006.[13] PAX CVS Repository, online available:http://isscvs.cern.ch/cgi-bin/viewcvs-all.cgi/?cvsroot=pax,2006.01020304050607080Format Problems, source editedBad or no PostScript fileBad FontsFigure ProblemsUnreadable disks/missing filesPaper too longEquation problemsAuthor requested changesPages numbered/empty etc241mmA4 paper (21.0 x 29.7 cm)US letter paper (8.5 x 11 in)0.2 in3.25 in9.5 in19mm (0.75 in)20mm (0.79 in)82.5mm5.0mm

Concepts, Developments and Advanced Applications of the PAX Toolkit

Concepts, Developments and Advanced Applications of the PAX Toolkit

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