Mantis a framework and toolkit for Geant4 simulation in CMS

1. Mantisa framework and toolkit for Geant4 simulation in CMS M. Stavrianakou CERN Geant4 Workshop 02.10.2002

2. COBRA Mantis OSCAR • COBRA is the CMS “framework”; it implements the CMS OO architecture • Mantis is the COBRA interface to Geant4 • Mantis as a subsystem of COBRA is • a toolkit for building or interfacing to detector geometries and sensitive volumes, generators, physics, magnetic fields, actions etc • a framework for Geant4 simulation applications (interactive or batch) • relies on COBRA infrastructure and services for core application steering and control, persistency, histogramming etc • provides run and event management • provides interfaces for loading the specific libraries for geometry, magnetic field, generators, physics, tuning and monitoring actions • OSCAR is the CMS Geant4 simulation based on Mantis ———————————————————————————————————————————————— Mantis is also: • a human able to see the future: from the Greek word for seer, prophet • a rather nasty insect • a very cute and timid shrimp M. Stavrianakou, CMS/CERN

3. Mantis functionality Application Steering • Mantis application (G4Application) is a COBRA SimApplication; it relies on COBRA for the application main • Most if not all configurable/tunable aspects of the application (including persistency) are driven by COBRA “simple configurables” (kind of “datacard”mechanism) • Persistency, metadata management, histogramming services etc are available transparently via the underlying COBRA infrastructure • G4Application instantiates and launches • an event source factory based on a COBRA abstract event “reader”of simulated events • a run manager and handles generator, magnetic field and visualisation selection and instantiation • powerful key COBRA features (lazy instantiation, action on demand, etc) and patterns (factories, dispatchers-observers etc) are used extensively (but are probably not yet exploited to their full potential) M. Stavrianakou, CMS/CERN

4. Mantis functionality Run and Event Management Run and event management are implemented in order to work around (what we may consider) restrictive Geant4 mechanisms and facilitate synergy with COBRA • Run Manager (inherits from G4RunManager) takes over control for: • geometry initialization • UserInitialization of a G4VUserDetectorConstruction bypassed • generator initialization and Monte Carlo event conversion to G4Event • G4VUserPrimaryGeneratorAction bypassed • physics initialization • UserInitialization of a G4VUserPhysicsList bypassed • Event • is a COBRA SimEvent • analogous to its Geant3 counterpart • manages Monte-Carlo truth • raw event/particles from generator and G4 simulated tracks and vertices • does not directly depend on Geant4, butneeds EventAction and Tracking Action to retrieve G4 simulated tracks and vertices M. Stavrianakou, CMS/CERN

5. Mantis functionality Geometry and Magnetic Field • Geometry: uses the CMS Detector Description Database (DDD) • Setup selection • full CMS, partial, test beam etc driven by configuration (XML) • Geometry building • automated conversion from DDD to Geant4 solids, materials, volumes • User limits • step and track length, production, tracking and time cuts: • automatic conversion and assignment from DDD to Geant4work in progress • no code modification, no recompilation, loadable on demand • Magnetic Field: uses the COBRA infrastructure and several COBRA-provided types of field, allowing • selection (Uniform, 2D map, 3D map) • interface to G4 with • choice of integrator • tuning options • loadable on demand M. Stavrianakou, CMS/CERN

6. Mantis functionality Sensitive Detectors and Hits • Sensitive detectors: creation and assignment to geometrical (logical) volumes • any number of instances of a given sensitive detector, assignable to any type and number of logical volumes • loadable on demand • Hits: COBRA hits and hit collections that handle • creation • using Geant4 ProcessStep • formatting • persistency • hit modelling, numbering scheme, readout choice by CMS detector group experts (OSCAR-side) • hits directly digitizable and usable by the CMS OO reconstruction program ORCA M. Stavrianakou, CMS/CERN

7. Mantis functionality Generators • infrastructure based on COBRA mechanisms and the COBRA GeneratorInterface • to produce a CMS RawHepEvent • converted and passed to Geant4 using the G4HEPEvtInterface • HepMC/HepPDT have been evaluated • will be used following evolution in context of on-going RTAGs • preference/recommendation for physical decoupling from CLHEP • to allow selection and configuration at the application steering level • implementations • configurable particle gun with choice of vertex generator • CMS HepEvt ntuple • CMS text file with choice of vertex generator • Pythia6 on-the-fly • loadable on demand M. Stavrianakou, CMS/CERN

8. Mantis functionality Physics and User Actions Physics Lists and Cuts infrastructure for • building a concrete physics list • list selection configuration • active categories of processes • general, electromagnetic, hadronic, ion … • selection of production (range) cuts: default, from file • currently using cuts per material User Actions infrastructure for • tuning • monitoring • quantities of interest (Begin/End Of Run/Event, Step, Pre/Post Track) “dispatched” to potential “observers” using COBRA dispatcher- observer pattern • at present foresee only one CMS “stacking action” possibly emulating level 1 trigger • any number of (combinations of) observers may be present • no need for central “action management” M. Stavrianakou, CMS/CERN

9. Mantis: the framework and its dependencies The core: G4Application M. Stavrianakou, CMS/CERN

10. Mantis as a toolkit CMS Geometry example CMS Sensitive Detector and Hits example M. Stavrianakou, CMS/CERN

11. Mantis as a toolkit CMS Production Physics List User Action Example M. Stavrianakou, CMS/CERN

12. A few last points • Mantis has been inspired by and developed in the context of COBRA • it has also been inspired by and reused ideas from Goofy (ATLAS) and has profited from the pre-existing OSCAR implementation • Interactivity is largely addressed by IGUANA • Mantis relies on basic G4 services/messengers; future versions may exploit emerging G4/Python facilities • Mantis amounts to ~5K lines of code developed by ~1 FTE in ~3 months • Realistic beta-testing by the CMS b/t – Tracker is in progress • vital feedback is contributing to improvements • There are outstanding requirements as well as currently unforeseen ones • Thanks to the underlying COBRA architecture, implementation of most new requirements is straightforward • Several requirements to Geant4 have emerged during the Mantis development • these we sometimes address as Geant4 shortcomings or restrictive mechanisms but this should not be taken as criticism in any negative sense; given the scope and magnitude of LHC experiment simulations, requirement evolution is inevitable • Mantis and the underlying COBRA infrastructure are not CMS-specific M. Stavrianakou, CMS/CERN