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Status and Plans for Geant4 Physics

Linear Collider Simulation Workshop III

2-5 June 2004

Dennis Wright (SLAC)

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Outline

Electromagnetic Physics– status and plans

– validation plots

Hadronic Physics

– status and plans

– validation plots

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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

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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 => don't use 6.0!

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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

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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 > 1 TeV– Precision of diff. cross section parameterization improved from

30% to 5%● New processes:

– above 1 TeV)

– e+e- (high energy)

● Old EM processes kept in 52

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Compton ScatteringData, G4 LowE , G4 standard

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Stopping Power Data, G4 LowE, G4 Standard

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Photoelectric EffectData, G4 LowE, G4 Standard

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Pair ProductionData, G4 LowE, G4 Standard

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Multiple Scattering (1)

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Multiple Scattering (2)

0.02130.0213(.0029)0.58 g/cm2 Pb

174 GeV

6.466.39(.18)1.82 g/cm2 Be

158.6 MeV

23.8824.00(.24)1.82 g/cm2

Pb

158.6 MeV

35.435.6(1.9)3.42 mg/cm2

Al

1.984 MeV

Geant4

0 (mr)

Data

0 (mr)

TargetProton energy

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BaBar EM Calorimeter (EM shower shapes)

Bhabha scattering data

Geant4

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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

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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

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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

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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

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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

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Gammas from 14 MeV Neutron Capture on U (Data driven model)

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Elastic Kaon Scatteringat 800 MeV/c

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Production from 730 MeV p(LEP Model)

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Production from 730 MeV p(Bertini Model)

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Multiplicity in pp Xat 200 GeV/c (QGS Model)

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Cross section for p Li + Xat 400 GeV (QGS Model)

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Atlas HEC (e/ ratio)

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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

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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

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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