simulations for cbm cbm-india meeting, jammu, 12 february 2008

Simulations for CBM

CBM-India Meeting, Jammu, 12 February 2008V. Friese

[email protected]

SQM03 Atlantic Beach

Simulations: Why?


Simulations for detector designConsequences:Many different detector designs / setups need being investigatedThe simulation framework must be flexible enough to enable an easy switch between geometries / digitisationsChallenge in particular for reconstruction (data structures, ...)


Simulation stepsExperiment DAQStepData levelData structures


CBMROOTCBMROOT is the CBM software framework for simulation, reconstruction and analysisIt is based on (FAIR)ROOT and VMCExecution via ROOT macrosCode is written in C++Documentation system is DOXYGENThe (current) build system is cmake, the distribution system is subversionSupported platforms are (almost) all Linux flavoursExternal packages used:GEANT3GEANT4ROOTCLHEPVMCPYTHIA


CBMROOT and FAIRROOTdetector specific (geometry, digitisation, ...)core (run manager, I/O, ...)CBMROOTFAIRROOTCBMROOTPANDAROOT

MVDSTSRICHTracking....basegeobaseparbase

MVDSTSRICHTracking....

basegeobaseparbase


Event generatorsProduces a list of particles, each with type, start vertex and momentum at start vertex, as input for the transportAvailable generator interfaces:Standalone (outside of the framework, with intermediate file)UrqmdGenerator (UrQMD output ftn14, ASCII)PlutoGemerator (PLUTO output, ROOT)ShieldGenerator (SHIELD output, ASCII)AsciiGenerator (self-written ASCII, defined format)Integrated (inside the framework, on the fly, without intermediate file)ParticleGenerator (single particles)BoxGenerator (particles with flat distribution in p, pt, y, )An arbitrary number of generators can be used at the same time


MC transportFAIRROOT employs the concept of Virtual Monte Carlo (VMC): The user can choose between different transport enginesAvailable engines:GEANT3GEANT4(FLUKA in preparation)The simulation run is controlled by the manager class CbmRunSimThe output is a ROOT tree. Branches are CbmMCTrack (input + secondary tracks) and objects derived from CbmMCPointCbmMvdPointCbmStsPoint....


MC Transport step by step1. Choose engine and create run CbmRunSim* fRun = new CbmRunSim(); fRun->SetName("TGeant3"); // Transport engine fRun->SetOutputFile(outFile); // Output file CbmRuntimeDb* rtdb = fRun->GetRuntimeDb(); fRun->SetMaterials/"media.geo");2. Define detector geometry CbmDetector* sts = new CbmSts("STS", kTRUE); sts->SetGeometryFileName(stsGeom); fRun->AddModule(sts);

3. Define magnetic field CbmFieldMap* magField = new CbmFieldMapSym3(fieldMap); magField->SetPosition(0., 0., fieldZ); magField->SetScale(fieldScale); fRun->SetField(magField);4. Define inputCbmPrimaryGenerator* primGen = new CbmPrimaryGenerator();CbmUrqmdGenerator* urqmdGen = new CbmUrqmdGenerator(inFile);primGen->AddGenerator(urqmdGen);fRun->SetGenerator(primGen);

5. ... and runfRun->Run(nEvents);


Detector simulation (digitisation)describes the detector response to the simulated MCTracksto be defined according to knowledge on the detectoroutput: CbmDigi for each active channelworkaround: HitProducer (e.g. Gaussian smearing of point)CbmStsPointCbmStsDigiCbmStsHitCbmStsDigitizeCbmStsFindHitsCbmStsPointCbmStsHitCbmStsHitProducer


The CBM setup: electronsmagnetRICHTRDTOFSTS + MVDECAL


The CBM setup: muonsSTS + MVDmagnetTRDECAL


Status of detector description

DetectorGeometry (MC)DigitisationMVDMonolithic stationsHitProducerSTSSegmented (sectors), support, cablesProjective strip geometry, hit finderRICHMonolithic (PM plane)HitProducerMUCHMonolithic stationsProjective pad geometry, avalanche simulation, cluster reconstructionTRDSegmented (sectors)HitProducerTOFSegmentedHitProducerECALOver-segmentedShower parameterisation


Example: STS


Example: MUCH


Event reconstructionis currently done in one step with digitisation (macro)manager class is CbmRunAnainput is MC data (output of transport simulation)The user defines tasks which areinitialised at the beginning of the runexecuted for each eventfinalised after the last eventoutput is a ROOT tree with branches for all data structures registered to the run manager by the class


Reconstruction step by step1. Create runCbmRunAna *run= new CbmRunAna();run->SetInputFile(inFile);run->SetOutputFile(outFile);

2. Register task(s)CbmTask* stsDigitize = new CbmStsDigitize(iVerbose);run->AddTask(stsDigitize);3. Initialise and start run run->LoadGeometry(); run->Init(); run->Run(0,nEvents);


Available reconstruction algorithms

TaskAlgorithmsOutputLocal STS trackingCellular AutomatonHough TransformCbmStsTrackLocal TRD trackingCellular AutomatonTrack followingCbmTrdTrackLocal MUCH trackingTrack followingCbmMuchTrackRICH ring findingHough TransformElastic NetCbmRichRingGlobal trackingGlobal TrackerCbmGlobalTrackMain vertex findingKalman FilterCbmVertex


Some resultsTrack reconstruction efficiency in MVD+STS, CA algorithm


Some more resultsRICH ring reconstruction with Hough transform


Electron identification capabilitiesComposition of identified electronsPion suppression


Performance of di-electron measurementsLow-mass vector mesonsAcceptance for meson


Performance of di-electron measurements (2)CharmoniaAcceptance for J/ meson


Open charm resultsD0, c=127 mK-+


Open charm results (2)c+ pK-+D0 ->K- - ++D+ ->K- ++
