Atlas Simulation Activities

• What is Geant 4

• Atlas Strategy

Geant4 - An Introduction

• What is Geant4?– A Toolkit to simulate the passage of particles

through matter– For Montecarlo simulation of the detectors in

High Energy Physics– Also for space and cosmic ray applications,

nuclear and radiation computations, heavy ions and medical applications

Geant4 - An Introduction (2)• An international collaboration

– Development based totally on object oriented software technology

– Re-use the experience and the algorithmic techniques accumulated with Geant3

– World-wide collaboration• ~100 Physicists, engineers, computer scientists• 15 countries all over the world• ~40 labs / institutes / universities• >10 experiments directly involved

• ~1/2 of the original collaborators from Atlas

Brief History - 1

• Pre-history– CERN: Investigation of class hierarchy for

GEANT (1993)– KEK: OO Analysis and Design of GEANT

(1993 Prodig Project, presented in CHEP94)

Brief History - 2• Geant4 as a CERN/DRDC R&D Project

– Approved at end 1994 as a 4 years project

– Milestones at end 1995:• Assessment of OO methods, full OOA&D• Geometry&tracking prototype + benchmarks

Achieved as scheduled

– Milestones at spring 1997• Alpha version comparable to GEANT 3.21• ODBMS persistency (hits)• Transparency of physics models for the users

Achieved as scheduled

Brief History - 3

• Milestones in 1998 (last year of the project)

• Release of a beta version (July) Achieved as scheduled

• Production version to be ready by the end of the year

Geant4 functionality -1

• Far beyond the functionality of the old GEANT3.21• Geometry

– Solid representations: CSG, BREP, SWEPT– ISO STEP compliant - CAD

• Parameterized volumes (solid and material), boolean operations

• Navigation– Integration of motion in any fields (electric, magnetic,

….)– Smart ‘Voxel’ method for an automatic optimization to

search volumes efficiently

Geant4 functionality - 2• Tracking and physics interactions

– Decouple tracking and physics implementations using a highly sophisticated OO design

– Easy to integrate a new physics process without knowledge of the tracking algorithm

– Coexisting of full and parametrized fast simulation• Electromagnetic interactions

– Electron and gamma physics from 10 KeV to 10TeV– Muon physics up to 1 PeV (data + theory)– Transition and synchrotron radiation, Cherenkov and

tracking of optical photon

Geant4 functionality - 3• Hadronic interactions

– OO redesigning of the existing shower code (GHEISHA)

– Enhancement of functionality from low to high energy using two models:

– Data driven models for low energy region – Theory driven models (string fragmentation and decay,

nuclear kinetics and intranuclear cascade,…) for high energy region

– Neutron transport using multiple data sets (ENDF/B+MENDL2)

Geant4 functionality - 4• Event handling

– General interface to existing event generators (Pythia, Isajet, ….)

– Multiple ‘physics runs’ in one job with different geometry, materials

– Tracks stacking mechanism with 3 priority levels for trigger studies to slow particles (loopers)

• Detector response and Data I/O– Hit and Digitization classes– Data I/O by ODBMS solution

Geant4 functionality - 5• Visualization and GUI

– Selection of multiple graphics systems • OpenGL, Inventor, DAWN, VRML, OPACS

– From high speed to engineering quality drawings• Engineering quality: DAWN• Virtual reality: VRML interface• Detector overlaps viewer: DAVID• GUI: GAG, XVT, OPACS

• Examples and User’s Manuals– Extensive examples covering full functionality– User’s manuals from novices to advanced applications– Installation guide for Unix and PC

Geant4 - Beta release

• Beta01 released in July 1998– Thorough bug shaking

• Currently working on Beta03 (Beta02 was just an internal checkpoint)

• Production version at the end of ‘98– Stable version– Missing functionality to be added in

subsequent releases

Atlas in Geant4 - 1

Atlas in Geant4 - 2

Atlas and Geant4• Implementation of the Atlas geometry already

started by our Japanese collegues a couple of yeas ago

• However:– A simulation program is more than detector

geometry– Want to be able to evaluate G4 and provide

feedback– Want to build an OO simulation framework– Want to merge with the rest of the Atlas software

OO simulation group - 1• Domain decomposition • High level design• Main areas of interest

– Integration in the Atlas mainstream– General framework and user interface– Facilities for geometry and detector description– Tools for implementing detector response and hits

storing– Memory management issues– Persistency and OODBMS

OO simulation group - 2• Start with a core group of Atlas-G4 members

– Domains, areas of interest, geographical splitting• Progressively enlarge the group as new people become

available/efficient– Interface definition, design cycles

• Rather aggressive schedule– 0th version of an OO simulation facility available

early spring– testbeam programs– Detailed Atlas geometry by fall ‘99?

Event generators and fast simulation -1

• Waiting for the next generqation of physics event generator to be written in OO/C++– Pythia 7 to be very much integrated with G4 since

the beginning• We are defining abstract interfaces for implementing

different kinds of event generators – Wrappers for the existing MC programs– Test beams– Single particle generators– Event overlaying– Interface to Objy

Event generators and fast simulation - 2

• Currently extracting Atlfast (the Atlas fast simulation program) from its root cradle to make it a standalone program (or, better, a toolkit)

• Exploit other (G) User Interface (e.g. have an LHC++ implementation)

• Consider the Geant4 way to fast simulation and study the possibility of implementing the Atlas fast simulation in G4– Look at what BaBar are doing

Prototypes and testbeams (1)

• Muon alignment system (DATCHA)– Simple Geometry– Interfacing to the existing (OO) pattern

recongnition program– Integration in the Arve framework

• Muon system description– Application of the Detector Description

package– Use of the Atlas field classes

Prototypes and testbeams (2)

• Simple calorimeters prototypes– Exploit the G4 physics– Hits, digits, OODBMS

• Tile calorimeter testbeam– Relatively simple geometry– First “operational” example

• Forward calorimeter/Hadronic endcap testbeams

• Accordion– Exploit the geometry part

Prototype and testbeams (3)

• TRT testbeam prototype– Test new features of the EM physics in G4– Relatively complicated example

• Silicon trackers (Pixels+SCT)– To be interfaced with existing pattern

recognition programs– Confront with current simulation

• Barrel sector prototype

Training• Examples

– Official code and home cooking

• Tutorials– Already started (during the Thursday

meetings, unfortunately just for people at CERN)

– Hope to have a more regular schedule

• Courses– To be organised with the help of IT division

Conclusions

• Geant4 Beta version released and made available for testing purposes

• On schedule for a Production release at the end of the year– Need for a stable version, already!

• Atlas activities are taking off rather steeply– G4 collaborators getting progressively free– New people joining the effort

• Physics TDR somewhat limiting people’s availability (in particular for physics studies)