Status and Plans for Geant4 Physics

1
Status and Plans for
Geant4 Physics

• Linear Collider Simulation Workshop III
• 2-5 June 2004
• Dennis Wright (SLAC)

2
Outline

• Electromagnetic Physics
• status and plans
• validation plots
• Hadronic Physics
• status and plans
• validation plots

3
Electromagnetic Physics Model
Approach

• Current status
• ionization, bremsstrahlung, multiple scattering
  are coupled due to reliance on pre-calculated
  energy loss tables
• Goal
• de-couple them by abstracting common behavior
• allow multiple physics models to be applied to
  each process
• allow models to be defined for given geometric
  region or energy
• Example
• can choose G4MollerBhabhaModel for energy loss
  and production of deltas by e/e-
• Or G4PAIModel for delta production by heavy
  charged particles

4
Electromagnetic Physics
Multiple Scattering

• Migration to Model Approach was to have been
  transparent to user, but bugs were introduced in
  Geant4 6.0
• width of angular distribution in MS became too
  large by 30
• only muons and hadrons were affected
• electrons OK
• other bugs as well
• mu ionization cross section 10 too small
• infinite loop for particles stopping in very low
  density gas
• Problems fixed by Geant4 6.1 gt don't use 6.0!

5
Electromagnetic Physics
Multiple Scattering

• New features
• improved transformation between geometric and
  true path length
• use Highland formula for Gaussian part of angular
  distribution for electrons
• option to allow backscattering at boundaries
• Plans
• Develop MS processes which are specific to muons
  and ions

6
Electromagnetic Physics
Other Processes

• Mu ionization
• addition of radiative corrections for energies
  above 1 GeV
• accurarcy of energy loss at high energy improved
  from 10 to 2
• Mu pair production
• updated parameterizations for E gt 1 TeV
• Precision of diff. cross section parameterization
  improved from 30 to 5
• New processes
• ????????????above 1 TeV)
• ee- ?????????(high energy)
• Old EM processes kept in 52

7
Compton ScatteringData, G4 LowE , G4 standard
8
Stopping Power Data, G4 LowE, G4 Standard
9
Photoelectric EffectData, G4 LowE, G4 Standard
10
Pair ProductionData, G4 LowE, G4 Standard
11
Multiple Scattering (1)
12
Multiple Scattering (2)
13
BaBar EM Calorimeter (EM shower shapes)
14

15
Hadronic Physics Lists

• Choosing the right combination of models is a
  complex task
• many models to choose from
• must mix and match according to physics goals
• Hadronic physics lists developed to make the job
  easier
• really just educated guesses
• meant as starting point for user to develop
  tailored physics list
• 24 hadronic physics lists currently provided
• 19 physics lists categorized according to 14 use
  cases
• url http//cmsdoc.cern.ch/hpw/GHAD/HomePage/
• all can be downloaded and installed as part of
  toolkit in directory parallel to source

16
Hadronic Physics Lists
Linear Collider

• LHEP
• low energy parameterized high energy
  parameterized models
• fast
• relatively easy to use
• not particularly good results below a few GeV
• LHEP_GN
• gamma- and electro-nuclear suite added
• QGSP_BERT
• quark gluon string Bertini cascade
• better results
• medium speed

17
Hadronic Physics Lists Linear
Collider

• QGSP_BIC
• quark gluon string binary cascade models
• best results overall
• slowest
• GQSP_HP, LHEP_HP
• high-precision neutron model added
• good for LC neutron fluxes

18
Hadronic Model Development

• Cascade models
• extend Bertini cascade to include kaons
• improve NN elastic and charge-exchange cross
  sections in Binary cascade
• optimize Binary and Bertini cascades for use in
  calorimeter physics lists
• String models
• reduce lower bound for QGS model to 6 GeV
• include anti-proton induced reactions
• attempt to improve shower shapes
• Chiral Invariant Phase Space model
• improved nucleon structure functions
• include neutrino-induced reactions

19
Hadronic Process Validation and Plans

• Physics testing
• thin target tests (comparing single Geant4
  process with data)
• full setup tests (full physics and full geometry)
• Statistical testing
• Too early, many models still under development
• Regression
• Some tests done currently, more are planned

20
Gammas from 14 MeV Neutron Capture on U (Data
driven model)
21
Elastic Kaon Scatteringat 800 MeV/c
22
Production from 730 MeV p(LEP Model)
23
? Production from 730 MeV p(Bertini Model)
24
Multiplicity in pp -gt Xat 200 GeV/c (QGS Model)
25
Cross section for p Li -gt ? Xat 400 GeV (QGS
Model)
26
Atlas HEC (e/? ratio)
27
Validation at Experiments

• ATLAS
• Test beam studies
• BaBar
• Running experiment
• Geant4 in production for two years
• GLAST
• Cosmic ray balloon tests
• HARP
• Running test beam experiment
• Results to be used to validate Geant4 thin target
  studies

28
HARP Experiment and Goals

• p and ? beams between 1.5 and 15 GeV/c on solid
  targets (Be through Pb) and liquid targets (H2 ,
  D2 ,N2 , H2O)
• Provide a systematic study of hadron production
  cross sections
• Will provide much-needed data for Geant4 hadronic
  model validation and tuning
• Data taking complete, analysis underway

29
Summary

• Electromagnetic physics
• model approach migration continues (bugs fixed)
• new models to be added
• statistical and regression tests being performed
• several processes are being extended
• Hadronic physics
• hadronic physics lists available as a first step
  toward developing a detailed physics list
• model development continues
• validation of hadronic physics continues