,Andreas Morsch, CERN EP/AIP CHEP 2003,Click to edit the title text format,Click to edit the outline text format,Second Outline Level,Third Outline Level,Fourth Outline Level,Fifth Outline Level,Sixth Outline Level,Seventh Outline Level,Eighth Outline Level,Ninth Outline Level,Simulation in ALICE,Andreas Morsch,For the ALICE Offline Project,2003 Conference for,Computing in High Energy and Nuclear Physics,Topics,ALICE Simulation Strategy,Simulation in the AliRoot Framework,Virtual MC,Event Generator Interfaces,ALICE Simulation Strategy (1),Coherent simulation framework for detector and physics performance studies in the AliRoot Framework based on ROOT,Physics simulation,Detailed detector response simulation,Fast simulation,Use of Transport MC transparent to the user,Virtual MC Interface,Maximum reuse of user code,One single development line (in C+),ALICE Simulation Strategy (2),Event Generator Interface tailored to the needs of the Heavy Ion Physics Community,Soft Uncorrelated Background,Correlations,Hard Processes,Maximum of flexibility and user configuration capabilities,Monte Carlo Truth,Full history from primary particles (partons) to hits available after simulation.,Root based Event Display,Root Based Interface to,G3 Geometry and Physics,AliRoot,Components Used in Simulation,run management,interface classes,detector base classes,data structure base classes,Detectors,ITS,PMD,PHOS,MUON,TPC,RICH,ZDC,CRT,TOF,TRD,FMD,STEER,EVGEN,PYTHIA,TGeant3,Geant3,MiniCERN,TGeant4,Geant4,User code for detector,simulation.,User code for,primary event,generation,Transport MC,START,EMCAL,VZERO,HIJING,TFluka,FLUKA,External Packages,Virtual Monte Carlo (VMC),User Code,VMC,Virtual Geometrical Modeller,G3,G3 transport,G4 transport,G4,FLUKA transport,FLUKA,Geometrical Modeller,Reconstruction,Visualisation,See presentation by Ivana Hrivnacova,See presentation by Andrei Gheata,Virtual Monte Carlo Status,TGeant3,Used in production,TGeant4,Used for Geant4 physics validation,See talk by Isidro Gonzalez,TFluka,Under development,Full chain from primary particle generation, transport, hits running,See also talk by Alberto Fasso on FLUKA physics,Simulation of Heavy Ion Collisions,Shortcomings of existing generators,None of the existing generators do give detailed account of the expected multiplicities, pt and rapidity dependence at LHC energies,Most of the hard probes (heavy flavor, jets .) are not properly reproduced by existing generators.,Existing generators do not provide for event topologies like momentum correlations, azimuthal flow etc.,The small cross-section of hard processes would demand prohibitively long runs to simulate a number of events that is commensurable with the expected number of detected events in the experiment,The ALICE Approach,The simulation framework provides an interface to external generators, like HIJING.,A parameterised “signal free underlying event with multiplicity as a parameter is provided.,Rare signals can be generated using,External generators like PYTHIA,Libraries of parameterised pt and rapidity distributions,The framework provides a tool to assemble events from different signal generators,On the primary particle level (cocktail),On the digit level (merging),After-Burners are used to introduce particle correlations.,Interface to external generators,Event Generator Interfaces,Interface to parametrisations,and decayer,Event Generator Interfaces,Container class for generators,Afterburner Processors,Introduction of correlations in otherwise uncorrelated events,2 particle correlations,Flow,Assembling of new events,Design of classes involved in event generation (,AliRun,AliStack,AliGenerator,) supports requirements for Afterburner,Example: Several objects of type,AliStack,containing the input events can be connected to the Afterburner (of type,AliGenerator,) to fill a stack connected to,AliRun,(output event),Fast Simulation,As many approaches as subdetectors.,Two main applications in ALICE:,Very fast simulation,Smearing of track parameters from paramterisation obtained from slow simulation,Combined slow and fast simulation,Detailed simulation of inner detector system (vertexing) and fast simulation of TPC response (momentum resolution),Conclusions,The ALICE Offline Project has developed a coherent simulation framework for detector and physics performance studies in the AliRoot Framework based on ROOT,The main simulation components are,Virtual MC Interface,TGeant3 (production),TGeant4 (physics validation),TFluka (implementation ongoing),Event generator interfaces tailored to the needs of the heavy ion community,