1. Mantis a framework and toolkit for Geant4 simulation in CMS
M. Stavrianakou
CERN
Geant4 Workshop

2. M. Stavrianakou, CMS/CERN
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
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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, but needs 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 Geant4 work 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. M. Stavrianakou, CMS/CERN
Mantis as a toolkit
CMS Geometry example
CMS Sensitive Detector and Hits example
M. Stavrianakou, CMS/CERN

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

12. M. Stavrianakou, CMS/CERN
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