1. Advanced Examples Maria Grazia Pia, INFN Genova
on behalf of the LowE-advanced examples WG
Geant4 D Review, CERN, October 2002

2. Advanced examples
Advanced examples are complete applications, corresponding to [simplified] typical real-life experimental situations
e.g. a test-beam set-up, a module of a detector etc.
They represent a valuable form of user support
They are developed in close collaboration with user groups
Users bring the knowledge of their experimental domain
Geant4 collaborators bring the knowledge of Geant4
The synergy of the two sides produces a valuable reference for other users
They are also playgrounds to identify new user requirements, or to verify the suitability of Geant4 for application to specific experimental problems
They illustrate not only the usage of simulation components in a typical experimental environment, but also of complementary “interactive” features, as needed in every-day life
graphics, (G)UI, histogramming, plotting the physics results of the simulation while it is still running etc…

3. The historical path
A directory examples/advanced was created in geant4 since the very first production release in December 1998
The actual development of Geant4 advanced examples was first proposed by the LowE e.m. Working Group soon after its creation in spring 2000
the topics of the advanced examples are not necessarily related to LowE e.m. physics
e.g. the currently LowE e.m. WG supports an example on LHC calorimetry, and the main LowE support comes from collaborators in a dark matter experiment!
this is an example of the collaborative spirit at the base of Geant4
The first 3 advanced examples were released in December 2000
Since then, 2 other advanced examples have been released
2 new advanced examples are at an advanced development stage
3 “LHC-like” advanced examples have been agreed
…and more are spontaneously proposed by users!

4. The process: inception
Advanced examples are proposed
either spontaneously by experimental groups on topics they consider of interest
or by members of the Geant4 Collaboration, as a response to identified needs of user support (in which case a “volunteer” collaborating user group must be found… which is not always easy!)
The proposed examples are presented to the TSB for inclusion in a future Geant4 release
In several cases the advanced examples have been proposed initially as “workshop projects” in the annual Collaboration Workshop, then evolved into longer term projects
The ex.-developers prepare a description of “what they want the software to do”
which the LowE WG transforms into a simple URD to establish the requirements for the example (the URD is then maintained by the LowE-advanced ex. WG)

5. The process: construction
Ex.-developers should provide at least an architectural design of the example, in response to the URs
in practice, users are often not familiar with OOAD…
so, pragmatically, we reverse engineer their code, and donate them the design models for further evolutions
The design is reviewed with Geant4 collaborators
we suggest improvements, better usage of toolkit components etc.
The implementation is done in close collaboration with Geant4 and Anaphe members
through the assistance of the LowE WG coordinator, example developers are put in contact with Geant4 experts to help them in the specific problems
The code is tested by the ex. development group
Of course, all this is carried on through an incremental and iterative process…

6. The process: deployment
The code is reviewed together with Geant4 collaborators
we would like to do more code reviews, but the resources are limited…
The examples are tested against the candidate global release tag prepared by the Release Manager at the end of the system testing phase
A documentation, consisting of a README + web page(s), is prepared by the ex.-developers
The ex.-developers update the requirements traceability matrix
The LowE WG coordinator assemble the existing material into a cohesive documentation
links to example documentation, URD, design diagrams, results, traceability etc.

7. The process: maintenance
Advanced examples must be maintained
evolutions in Geant4, in AIDA, in the supported platforms, in the user requirements etc.
Often the whole workload of maintenance falls on the LowE WG
it is a significant workload
as well as the support during the construction phase
Advanced examples facilitate the user support process
Often, the response to a user question is “look into advanced example X, class Y, and you’ll find a solution to a problem quite similar to yours”

8. Analysis In real life simulation is often accompanied by analysis
Histograms, ntuples to plot relevant distribution resulting from the simulation
UR: possibility to plot histograms while the simulation is running, to monitor whether everything looks fine, or to decide when to stop the accumulation of statistics
All advanced examples adopt AIDA (Abstract Interfaces for Data Analysis)
To avoid introducing into Geant4 dependencies from any specific analysis tool
Users can choose their preferred analysis system (without having to change one single line of code) by loading the appropriate shared library
Documentation in
Close collaboration with the AIDA team
Very valuable support to ex.-developers and users by the Anaphe team

9. Underground physics mirror LXe GXe source PMT
A liquid Xenon cell, with a typical underground background environment
Record scintillation light in PMs
Physics: neutrons, LowE processes for ions, scintillation, radioactive decay module etc.
Full lab geometry (important for n scattering)
Cavern + door, cupboards, desks in the experimental environment
Xenon vessel accurately reproducing a real prototype
Complex primary generator (GPS)
LXe
GXe
PMT
mirror
source

10. X-ray fluorescence Test beam set-up of a typical X-ray analysis
A photon beam impinging on a material sample; the fluorescence spectrum of the material is measured by a semiconductor detector
Physics: Low Energy processes, atomic relaxation
Scattered
photons
Fe lines
GaAs lines
sample
detector
beam

11. g telescope A tracker + a calorimeter + a veto counter
Standard electromagnetic processes
Example of how to build a simple trigger out of digitised signals
How to plot histograms with physics distribution while the simulation is running

12. X-ray telescope The first advanced example
Originally a “workshop project” (Geant4 Workshop 1999, hosted by ESA)
A module of a Chandra/XMM-like telescope
Physics for space radiation background studies
Well documented example of how to use a variety of visualisation drivers, various (G)UI options, GGE, GPE, histograms, ntuples etc.

13. brachytherapy
A general purpose application for the calculation of dose distributions from a radiotherapy source
Fancy geometry to configure different brachyterapy techniques in the same application
How to create/destroy/replace a geometry at run-time
Low energy electromagnetic processes for precise calculation of dose distribution
Developed in collaboration with cancer research groups in hospitals

14. In preparation Gravitational waves experiment
Space charging
LHC-like test beam set-ups
Atlas-like electromagnetic calorimeter
CMS-like electromagnetic calorimeter
LHCb-like RICH
Radioprotection
Contamination from radioactive isotopes in human body (and environment?)
IORT
Model of a compact accelerator
…and more to come

15. More information in http://www.ge.infn.it/geant4/lowE/index.html
Conclusions
The advanced examples have been created in response to typical user questions
They offer (simplified) solution to real-life experimental situations
They offer a valuable user support
GLAST simulation started from the gammaray_telescope example
underground_physics (developed by UKDM) has become the reference for many experiments at the Gran Sasso Lab
brachytherapy has become a “classic” for radiotherapic dosimetry
Users’ feedback is very positive
More information in