1. ALICE Simulation Framework Ivana Hrivnacova 1 and Andreas Morsch 2 1 NPI ASCR, Rez, Czech Republic 2 CERN, Geneva, Switzerland For the ALICE Collaboration International Conference on COMPUTING IN HIGH ENERGY AND NUCLEAR PHYSICS Padova, February 9, 2000

2. 9 February 2000CHEP 2000, Padova2 Outline  Setting the scene ¦ goals and priorities ¦ AliRoot framework  Interfaces to simulation components ¦ Monte Carlo ØGeant4 application status in this context ¦ event generator ¦ segmentation

3. 9 February 2000CHEP 2000, Padova3 Strategy  Distinction between immediate and long-term requirements.  Assure coherence of the whole simulation process: ¦ event generation ¦ particle tracking ¦ signal generation ¦ digitization ¦ fast simulation  Reuse of existing code and knowledge (people): ¦ Geant3 based simulation code ¦ users come with FORTRAN+PAW+CERNLIB background

4. 9 February 2000CHEP 2000, Padova4 Strategy Short And Long Term Goals  Short term requirements: ¦ simulations are needed for: ØTechnical Design Reports, detector design optimization, integration of new detectors ¦ profit from OO design as early as possible ¦ allow for evolution  Long term goals: ¦ smooth transition to Geant4 ¦ reuse of Geant3 based simulation user code: ¦ possible integration of other tracking codes Ø fast simulators, FLUKA,...

5. 9 February 2000CHEP 2000, Padova5 AliRoot  AliRoot = the ALICE off-line framework for simulation, reconstruction, and analysis ¦ OO design, C++ ¦ Geant3 and some legacy code in FORTRAN  Based on ROOT framework

6. 9 February 2000CHEP 2000, Padova6 run management interface classes detector base classes data structure base classes AliRoot Components Used in Simulation Detectors ITSPMDPHOSMUONTPCRICH ZDCCASTORTOFTRDFMD STEER EVGEN PYTHIA TGeant3 Geant3MiniCERN g4mcaliceG4 Geant4

7. 9 February 2000CHEP 2000, Padova7 Monte Carlo Interface  Pure abstract class AliMC  It has been developed as generalization of G3 functions for definition of simulation task  Provides methods for ¦ geometry description definition ¦ physics process control ¦ access functions to tracking particle properties ¦ visualization

8. 9 February 2000CHEP 2000, Padova8 Monte Carlo Interface Implementations  For Geant3 = TGeant3 class ¦ up and running  For Geant4 = g4mc package ¦ in development ¦ each domain is covered by its manager class: geometry, physics, stepping, visualization, run ¦ each manager uses corresponding category(ies) of G4  For FLUKA = no implementation yet ¦ on the wish list

9. 9 February 2000CHEP 2000, Padova9 Monte Carlo Interface Implementation for Geant4

10. 9 February 2000CHEP 2000, Padova10 MC Implementation for G4 Geometry (1)  Geometry manager as client of g3tog4 (stand-alone package provided by Geant4 for automatic conversion of G3 geometry)  This development resulted to our contribution to g3tog4 in Geant4  In difference from standard usage of g3tog4 the input geometry is not the ZEBRA file (converted to ASCII file) but the C++ code in detector classes in AliRoot ¦ for debugging reasons the ASCII file can be generated from AliRoot, read back and process by standard g3tog4 tool, too

11. 9 February 2000CHEP 2000, Padova11 MC Implementation for G4 Geometry (2)  Almost all G3 options for geometry definition are supported ¦ passing parameters from mother volume to its daughters ¦ divided volumes - represented by replicated physical volumes in G4 (G4PVReplica)  Unsupported option: “MANY” ¦ “MANY” option substitutes lack of Boolean operations in G3 geometry

12. 9 February 2000CHEP 2000, Padova12 MC Implementation for G4 Physics  Physics manager provides G4 physics list construction from G3 cuts and physics process control parameters  G3 tracking media parameters are applied to G4 logical volumes with usage of ¦ user limits (derived class from G4UserLimits) ¦ special cuts process (derived class from G4VProcess) ¦ special flags (process control) process (derived class from G4VProcess)  In development ¦ only subset of G3 parameters is supported ¦ more testing needed

13. 9 February 2000CHEP 2000, Padova13 MC Implementation for G4 Stepping, Visualization, Run  Stepping ¦ step manager class works as adapter between the MC interface (AliMC) and G4 step manager (G4StepManager) ¦ access to properties of the tracking particle during stepping ¦ complete  Visualization ¦ visualization manager class is designed to adapt the MC interface methods to G4 visualization ¦ work has been started recently  Run Management ¦ run manager class provides G4 run control to the application main program or its manager (AliRun in AliRoot)

14. 9 February 2000CHEP 2000, Padova14 Monte Carlo Interface ALICE Geant4 Geometry Detectors: TPC, RICH, FMD, CASTOR, MUON, PHOS, PMD, ZDC Structures: HALL, ABSO, DIPO, FRAME, MAG, PIPE, SHIL

15. 9 February 2000CHEP 2000, Padova15 Event Generator Interface  Class AliGenerator  Purpose: to generate primary particles to be tracked and to put them on the stack  Functions: ¦ make generator known to the run manager (AliRun) ¦ set kinematic selection (momentum, pT, phi, theta, y) ¦ set vertex position and smearing (sigma, per event, per track) ¦ set child particle and parent particle weight  It can be also used ¦ to write primary particle event files ¦ as input to fast physics simulation

16. 9 February 2000CHEP 2000, Padova16 Event Generator Interface Implementations  External generators: Pythia  External event files  Parameterizations (y, p T, particle cocktail)  Boundary sources as interface to FLUKA  Testing tools: particle guns, …

17. 9 February 2000CHEP 2000, Padova17 Event Generator Interface Generator Cocktail  Recursive implementation of AliGenerator  Enables to compose event from more different generators

18. 9 February 2000CHEP 2000, Padova18 Event Generator Interface Interface to FLUKA FLUKA AliRoot ALIFE Boundary Source

19. 9 February 2000CHEP 2000, Padova19 Segmentation Interface  Class AliMUONSegmentation  Common “behavior” of detector segmentation: ¦ pad to real coordinate transformation ¦ iteration over pads ¦ providing pad neighbors ¦ access functions to geometry  Segmentation of Muon Chambers are used in ¦ signal generation (spreading charge over pads) ¦ recursive cluster finding ¦ hit reconstruction from clusters ¦ visualization of hits together with resulting clusters

20. 9 February 2000CHEP 2000, Padova20 Segmentation Interface Muon-arm Hit Reconstruction  irregular segmentation  the same technology, different segmentation layout

21. 9 February 2000CHEP 2000, Padova21 Summary  ALICE uses ROOT based OO framework for simulation and reconstruction (AliRoot)  interface classes provide modularity and coherence of the simulation process  the Monte Carlo interface allows: ¦ to build Geant3 and Geant4 application from the same user code ¦ to test Geant4 under the same conditions: geometry, signal generation, output data structures ¦ to define Geant3 application in C++  interface classes can be reused in other architectures