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The CMS Simulation Software

The CMS Simulation Software. Julia Yarba, Fermilab (for the CMS Collaboration) IEEE/NSS 2006 Oct 30 – Nov 2 2006 San Diego, California (USA). Overview.

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The CMS Simulation Software

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  1. The CMS Simulation Software Julia Yarba, Fermilab (for the CMS Collaboration) IEEE/NSS 2006 Oct 30 – Nov 2 2006 San Diego, California (USA)

  2. Overview • Though in operation for a number of years, it’s a live system – goals, requirements, tools evolve throughout the lifetime of the experiment • Based on Geant4 (7.1; in transition to 8.1): • physics processes: electro-magnetic and hadronic interactions • tools for detector geometry and sensitive element response • interfaces for tuning and monitoring particle tracking • New CMS offline framework and Event Data Model: • Manages application control at run time • Relies on the concept of event processing module (EDProducer) • Interface to common tools (generators, mag.field, MC truth…) • Ensures provenance tracking and event immutability Julia Yarba, FNAL – IEEE/NSS 2006

  3. Simulation Software – CMS Solution CMSSW – the new framework - ties pieces together Application control Object browsing Event generation PYTHIA, Particle Gun, … User Actions HepMC Visualization Mixing Module User Actions User Actions User Actions Simulation Geant4 (+FAMOS+GFlash) SimHit Data File (Hit level information, linked to MC truth) Validation Suite Geometry Detector Description Database (XML & C++) + Sensitive Volumes Interface Digitization subsystem-specific packages Digi data file (Data-like, linked to MC truth) Misalignment Simulation (under development) ROOT – based persistency format Reconstruction Julia Yarba, FNAL – IEEE/NSS 2006

  4. Interface to Geant4 • Core application = framework-based Event Data Producer + customized RunManager as interface between Geant4 and CMS Event Data Model • Geometry record is available to either simulation or reconstruction via the framework EventSetup; uses XML-based Detector Description machinery, configurable at run time via a hierarchy of XML files; converts DD solids and materials to Geant4 counterparts • Sensitive detectors associated with geometrical volumes through XML configuration files at run time • Magnetic field based on dedicated geometry of magnetic volumes; provided by independent subsystem via EventSetup; field selection, propagation tuning configurable at run time Julia Yarba, FNAL – IEEE/NSS 2006

  5. Interface to Geant4 (cont.) • Variety of lists (LHEP, QGSP/QGSP_EMV, QGSC, FTFP,…) for modeling physics processes; run-time selection of physics list and production cuts, activation/tailoring of individual processes; • Variety of Physics event generators (particle guns, Pythia, Herwig,…); generator information stored in HepMC format and interfaced to G4Event • User actions allow access to Geant4 objects at any stage (run, event, track, step); used for tuning, diagnostics, custom bookkeeping • Monte Carlo truth record with decay/interaction history of the generator’s particles and selected tracks from Geant4 simulation Julia Yarba, FNAL – IEEE/NSS 2006

  6. The CMS Detector Different subsystems have different simulation requirements  Region based optimization • 22 m long, 15 m in diameter • Over a million geometrical volumes • Many complex shapes Julia Yarba, FNAL – IEEE/NSS 2006

  7. Central Detector Subsystems Simulated tracks and hits in CMS Tracker • Tracker (talk by F.Ambroglini): • Critical region, due to its own physics • significance, and the effect on the overall • simulation accuracy • Detailed geometry description of active and • passive volumes • Extensive validation – single particle, minbias, • physics channels Simulated tracks and energy deposition in CMS ECAL • Electromagnetic calorimeter (talk by F.Cossutti): • Resolution dominated by effects not included in • shower simulation • Excellent agreement between test beam and • Geant4 simulation • Highly sensitive to changes in radiation, showering • in tracker Julia Yarba, FNAL – IEEE/NSS 2006

  8. Central Detector Subsystems (cont.) • Hadronic calorimeter: • Test beam data available (2002-2004, • various HCAL modules, preceded • by ECAL prototype; e, π, and μ beams) • Agreement with simulation within large • systematic uncertainties of the data • Sensitive to accuracy of the Geant4 • modeling of hadronic showers; results • depend on the choice of physics list HCAL response linearity vs energy H(150)ZZ4µ • Muon system: • Comparison G3/G4 with single  10-104GeV • Improvements in Geant4: µ brem., e+e- prod., • µ-nuclear interactions, multiple scattering • Test beam setup: • 2 chambers with or without iron slab, to study • effect of  showers in passive material Julia Yarba, FNAL – IEEE/NSS 2006

  9. Forward Subsystems • Essential for diffractive and Heavy Ion programs: • CASTOR calorimeter • Totem telescopes • Zero Degree Calorimeter • Simulation to study energy resolution, leakage; analysis of test beam data (Nov.05) • Other components • Roman Pots • Luminosity Monitor Totem Telescopes at 7.5 < z < 13.5m Castor Calorimeter at 14.37 m (5.3 <h< 6.7) Julia Yarba, FNAL – IEEE/NSS 2006

  10. Event Mixing and Digitization • In-time pileup : LHC will produce ~3 (“low lum.”) or ~25 (“high lum.”) minbias interactions/crossing, on top of the trigger event • Out-of-time pileup: Coming from bunch crossings before/after the trigger event • Pileup events simulated separately from the physics events; merge of simulation outputs at hit level (reuse) • Performed by a dedicated module, in a separate step • Followed by simulation of the electronic readouts (Digi’s) • Dedicated Digi module for each subsystem (separate steps) Julia Yarba, FNAL – IEEE/NSS 2006

  11. …… Tracks Muon Vertex Performance Global Global Electron Jet/MET Mix Generator Sample Simulated Hits Digitized Hits Reconstructed Hits/Objects Geometry ECal Track ECal Track ECal Track Field HCal Muon HCal Muon HCal Muon Software Validation (talk by X.Huang) • Validation of physics processes modeling, via dedicated test beam setup simulation compared vs test beam data – feedback to Geant4 • Software Validation Suite, to ensure simulation (or other) software reliability, release-to-release, when changing Geant4 version, etc… • Proved very useful, in particular in recent tests of Geant4.8.1-based version Julia Yarba, FNAL – IEEE/NSS 2006

  12. Performance and Production • With the new/upgraded software: over 60 millions events simulated by the production team since July 2006 (CSA06) • Failure rate: ~1/104 Expected to improve as we switch to Geant4.8.1 • Speed (3.6GHz CPU, Geant4.8.1 with QGSP_EMV physics list, interactive testing) very preliminary : Minimum bias events : 37 seconds per event H  eeμμ : 197 seconds per event • CMS strategy: equal number of simulated and real events (~ 1.5x109/year) Aim to achieve this with a mixture of full and fast simulation Julia Yarba, FNAL – IEEE/NSS 2006

  13. Summary and Outlook • In CMS, the Geant4-based Object Oriented simulation has been successfully implemented • Ported to the new framework, widely validated (feedback reported to Geant4), used for physics and detector studies • Proven to be robust, powerful, maintainable • Capable to fulfill emerging requirements • Further developments : • Finalize geometry updates (ECAL,…) • Include shower parametrization (GFlash, hadronic) • Performance improvement (Geant4.8.1, local magnetic field stepper…) Julia Yarba, FNAL – IEEE/NSS 2006

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