S. Chauvie,G. Depaola, F. Longo, V. Ivanchenko, P. Nieminen, M.G. Pia

1
ow Energy Electromagnetic Physics
http//www.ge.infn.it/geant4/lowE/index.html

• S. Chauvie,G. Depaola, F. Longo, V. Ivanchenko,
  P. Nieminen, M.G. Pia
• on behalf of Geant4 Low Energy Electromagnetic
  Working Group
• Budker Inst. Novosibirsk - CERN - Univ. of
  Cordoba - ESA
• INFN (Ferrara, Genova, Torino,Trieste)

CHEP 2001 Conference Beijing, 3-7 September 2001
2
Low energy e/g models in
Cosmic rays, jovian electrons
were triggered by astrophysics requirements
X-Ray Surveys of Asteroids and Moons
Solar X-rays, e, p
Geant3.21
ITS3.0, EGS4
Courtesy SOHO EIT
Geant4
Induced X-ray line emission indicator of target
composition (100 mm surface layer)
C, N, O line emissions included
Courtesy ESA Space Environment Effects Analysis
Section
3
Dark matter searches
From deep underground to galaxies
AGN
From crystals to human beings
GLAST
4
A growing interest

• The activity on Geant4 Low Energy Electromagnetic
  Physics started in October 1998
• Part of the RD44 electromagnetic category, 1 ESA
  contractor
• Continued as a subset of Geant4 general
  Electromagnetic Working Group (2 people)
• Initially meant to be one of the ESA modules
  for space radiation studies, limited to electron
  and photon processes
• The scope of the activity extended soon
• Physics wide set of models
• Applications also HEP, astrophysics, medical
• Independent Geant4 Low Energy Electromagnetic
  Working Group created in April 2000 (9 members
  initially)
• 53 members now
• Contacts in progress with new people interested
  to collaborate

2000
2001
5
How we operate
Rigorous approach to software engineering Rich
and transparent physics Goal-directed project
management
Physics Applications
Wide spectrum of development
Team

• Ample coverage of expertise
  (theory, experimental, software)
• Emphasis on training of group members

Collaboration

• Promotion of cross-WG activities
• Close relationship with user communities

Outreach

• Active strategy of information
• Promotion of technology transfer

6
Software Process

• A rigorous approach to software engineering
• in support of a better quality of the software
• especially relevant in the physics domain of
  Geant4-LowE EM
• several mission-critical applications (space,
  medical)

A life-cycle model that is both iterative and
incremental
Spiral approach
Collaboration-wide Geant4 software process,
tailored to the WG projects (see talk on Geant4
Software Process by G. Cosmo)

• Public URD
• Full traceability through UR/OOD/implementation/te
  st
• Testing suite and testing process
• Public documentation of procedures
• Defect analysis and prevention
• etc.

• Huge effort invested into SPI
• started from level 1 (CMM)
• in very early stages chaotic, left to heroic
  improvisation

current status
7
User Requirements
Various methodologies adopted to capture URs

• Elicitation through interviews and surveys
• Useful to ensure that UR are complete and there
  is wide agreement
• Joint workshops with user groups
• Use cases
• Analysis of existing Monte Carlo codes
• Study of past and current experiments
• Direct requests from users to WG coordinators
• Prototyping
• Useful especially if requirements are unclear or
  incomplete
• Prototype based on tentative requirements, then
  explore what is really wanted

Posted on the WG web site

• Not only functional requirements, users also
  ask for
• Proof of validation of the physics
• Documentation
• Examples of application in real-life set-ups

Specification PSS-05 standard
Analysis in WG workshops
Maintenance under configuration management
User
requirements evolve and we should be able to
cope with their evolution!
8
OOAD
Technology as a support to physics
Rigorous adoption of OO methods ? openness to
extension and evolution Extensive use of design
patterns Booch methodology
9
Hadrons and ions
Open to extension and evolution
Physics models handled through abstract classes
Algorithms encapsulated in objects
Transparency of physics, clearly exposed to users
Interchangeable and transparent access to data
sets
10
Data Management
Very important domain physics models based on
the use of evaluated databases
Intelligent data know how to handle themselves
through algorithm objects e.g. interpolation
algorithms encapsulated in objects (to let them
vary and be interchangeable) Composite pattern to
treat different physical entities (e.g. whole
atom and atom with shell structure) transparently
11
Photons
12
Atomic relaxation
Domain decomposition leads to a design open to
physics extensions
13
Testing
Integrated with development (not something to do
at the end)

• Suite of unit tests (1 per class)
• Cluster testing
• 3 integration/system tests
• Suite of physics tests (in
  progress with publications)
• Regression testing
• Testing process
• Testing requirements
• Testing procedures
• etc.
• Physics validation

XP practice write a test before writing the
code recommended to WG developers!
14
Electron and Photon processes

• Validity range 250 eV 100 GeV
• 250 eV is a suggested lower limit
• data libraries down to 10 eV
• 1 lt Z lt 100
• Exploit evaluated data libraries (from LLNL)
• EADL (Evaluated Atomic Data Library)
• EEDL (Evaluated Electron Data Library)
• EPDL97 (Evaluated Photon Data Library)
• for the calculation of total cross section and
  generation of the final state

• Compton scattering
• Rayleigh scattering
• Photoelectric effect
• Pair production
• Bremsstrahlung
• Ionisation
• atomic relaxation

15
Photon attenuation comparison with NIST data
Testing and Validation by IST - Natl. Inst. for
Cancer Research, Genova
Pb
water
Fe

• ? Low Energy EM
• Standard EM
• w.r.t. NIST data

accuracy within 1
Courtesy of S. Agostinelli, R. Corvo, F.
Foppiano, S. Garelli, G. Sanguineti, M. Tropeano
16
Polarisation
Cross section

• Integrating over ?
• Sample ?
• ? - Energy Relation ? Energy
• Sample of ? from P(?) a (b c cos2 ?)
  distribution

Sample Methods
Low Energy Polarised Compton
250 eV -100 GeV
Scattered Photon Polarization
More details talk on Geant4 Low
Energy Electromagnetic Physics

• ? Polar angle
• ? Azimuthal angle
• ? Polarization vector

Other Low Energy Polarised Processes under
development
17
Hadron and ion processes
Variety of models, depending on energy range,
particle type and charge

• Density correction for high energy
• Shell correction term for intermediate energy
• Spin dependent term
• Barkas and Bloch terms
• Chemical effect for compound materials
• Nuclear stopping power

Positive charged hadrons

• Bethe-Bloch model of energy loss, E gt 2 MeV
• 5 parameterisation models, E lt 2 MeV
• based on Ziegler and ICRU reviews
• 3 models of energy loss fluctuations

Positive charged ions

• Effective charge model
• Nuclear stopping power

• Scaling
• 0.01 lt b lt 0.05 parameterisations, Bragg peak
• based on Ziegler and ICRU reviews
• b lt 0.01 Free Electron Gas Model

Negative charged hadrons

• Parameterisation of available experimental data
• Quantum Harmonic Oscillator Model

• Model original to Geant4
• Negative charged ions required, foreseen

18
Some results protons
19
Some results ions and antiprotons
Ar and C ions
20
Application examples

• Three advanced examples developed by the LowE EM
  WG released in December 2000 as part of the
  Geant4 Toolkit (support process)

• X-ray telescope

• g-ray telescope

• brachytherapy

Full scale applications showing physics
guidelines and advanced interactive facilities in
real-life set-ups

• More in progress
• Underground physics and radiation background
• X-ray fluorescence and PIXE

Extensive collaboration with Analysis Tools
groups (see talk by A. Pfeiffer, Architecture of
Collaborating Frameworks)
21
User applications
No time to mention them all!
See also other talks Simulation for
astroparticle experiments (this session) From HEP
computing to bio-medical research (plenary)
22
Conclusions

• New physics domain in HEP simulation
• Wide interest in the user community
• A wealth of physics models
• A rigorous approach to software engineering
• Significant results from an extensive validation
  programme
• A variety of applications in diverse domains

23
http//www.ge.infn.it/geant4/lowE/index.html