Status and Plans for Geant4 Hadronics
Dennis Wright (SLAC)
SPENVIS & Geant4 Space Users' WorkshopLeuven, Belgium3-7 October 2005
Outline
● Brief introduction to Geant4 hadronics● Development plans
– of interest to the space applications community● ion interactions● radioactive decay
– of general interest● Low Energy Parameterized model improvements● Chiral Invariant Phase Space (CHIPS) model extensions● extending high energy models
● Hadronic highlights of the 7.1 release
Hadronic Physics in Geant4
● User is responsible for building an appropriate physics list – select particles to use
– add processes to particles
– register models to processes
● Geant4 in general and G4 hadronic physics in particular provides much freedom in this– this is a mixed blessing!
– only 5 hadronic process types to choose from, but ~40 models
– current Geant4 policy: no default processes or models● to a novice user, this can be confusing● pre-built physics lists partly address this issue
particle
at restprocess 1
in-flightprocess 2
process3
processn
model 1model 2
.
.model n
c.s. set 1c.s. set 2
.
.c.s. set n
Cross sectiondata store
Energy range
manager
1 MeV 10 MeV 100 MeV 1 GeV 10 GeV 100 GeV 1 TeV
LEP
HEP ( up to 15 TeV)
Photon EvapMultifragmentFermi breakup
Fission
EvaporationPre-
compound
Bertini cascade
Binary cascadeQG String (up to 100 TeV)
FTF String (up to 20 TeV)
High precision neutron
At rest Absorption
K, anti-p Photo-nuclear, electro-nuclear
CHIPS (gamma)
CHIPSHadronic Model Inventory
LE pp, pn
Rad. Decay
Development Plans(relating to space applications)
● Binary light ion cascade model (mass range)– basic assumption limits use to 12C projectiles and lighter:
interaction of “participants” (nucleons in projectile + secondaries from target) is ignored
– should be a big effect for heavy projectile – heavy target collisions
– we are now studying its extension to higher mass projectiles● results look promising, despite limiting assumption● tested for some medium-mass projectiles
Neutron production - 400 MeV/n 12C on Pb
Neutron production - 400 MeV/n 40Ar on Pb
Development Plans(relating to space applications)
● Energy range of ion transport models in Geant4– current limit of Binary Light Ion cascade is ~ 10 GeV/n
– low energy limit is ~80 MeV
– other models can go higher● URQMD● JQMD● JAM
– but they are currently external to Geant4● interfaces exist for JQMD and JAM
Development Plans(relating to space applications)
● High precision neutron models – cannot currently handle all elements
– data for Hg, Gd, etc. missing
– need to create new entries for high precision neutron data library G4NDL
– not found in ENDF, JENDL, etc.
– need to collect cross sections, final state multiplicity and angular distributions from 0 – 20 MeV
Development Plans(relating to space applications)
● Radioactive Decay Process– designed to provide -decayselectron capture,
isomeric transition– decay table entries with short lifetimes need to be completed
● examples: 8Be, 5Li● need to add decay mode, daughter excitation energy, intensity
– add proton and delayed neutron decay channels● examples: 6Be, 7B
Development Plans(of general interest)
● Low Energy Parameterized Models– the nuclear de-excitation part of this model is rather simple:
● after the intra-nuclear cascade stage, goes straight to evaporation ● evaporation stage is highly parameterized -> doesn't do as well
as other models available at low energies– add more detailed, nucleus-dependent parameterization
● requires looking at evaporation data and re-evaluating the parameterizations
– general re-factoring of all LEP code● still many holdovers from old GHEISHA code
Development Plans(of general interest)
● Bertini cascade– improve angular distributions of kaon-induced, 2-body final
states● these are the channels with the largest cross sections● also lots of angular distribution data
– begin validation of higher energy data● things look good at 1GeV and below, what about 1 – 10 GeV ?● some data exist (1 – 3 GeV)● more coming from test beam experiments
Development Plans(of general interest)
● Bertini cascade– begin testing and validation of elastic and quasi-elastic
scattering● code has so far always been used for inelastic scattering● it is set up to do elastic, but has not yet been validated● would be a very useful alternative to the LEP elastic
– explore using Bertini cascade for ion-ion collisions● most of the machinery already exists ● about 1 year required to add necessary code and for testing● perhaps a useful alternative to Binary Light Ion Cascade
Development Plans(of general interest)
● Binary cascade– propagate interface to string models
● high energy models could then use Binary cascade directly as a de-excitation stage
– look at extending to kaons● difficult problem because the model deals explicitly with
resonances, and there are so many when a strange quark is added – look at extending to higher energies
● current limit is 10 GeV for p,n, 1.3 GeV for pi+, pi-
Development Plans(of general interest)
● Chiral Invariant Phase Space (CHIPS) model– currently used for gamma- and electro-nuclear processes
● interface to CHIPS does not conserve charge: virtual photon is converted 50% to pi+, 50% to pi-
● need to interact photon directly with nucleus– look into extending to muon-nuclear processes
– look at extending to higher energies ( > 5 GeV)● CHIPS now used in Geant4 as a nuclear de-excitation model● could be used to replace quark-gluon string model● use a quasmon string (Herwig-style fragmentation) instead of
quark-gluon string (Pythia-style fragmentation)
CHIPS Quasmon (as used in Electro-nuclear model)
*
Development Plans(longer term)
● Neutrino interactions– becoming more important now that large detectors are coming
into operation
– CHIPS model to be used to implement interactions ● incoming neutrino interacts with a nucleon, forming a quasmon● quasmon decays into hadrons
– energy limit ~5 GeV incident
Development Plans(longer term)
● High energy models– re-factor high energy parameterized model (remove vestiges of
GHEISHA)
– extend QGS, FTF models● current upper limit is ~ TeV ● but no Geant4 model has yet incorporated minijets -> effectively
limits validated energy to 100 GeV ● consider adding code from HE event generators, such as
DPMJET which can go to 2000 TeV
Development Plans(longer term)
● Multiple scattering of hadrons– currently Geant4 treats all processes independently – no
interference between hadron and EM processes
– interference effects could be as large as 100%
– code design problem● interdependency between EM and hadronic sectors now required
Highlights: Coherent elastic hadron scattering from nuclei
● Introduced in the 7.0 release● Improved angular distributions for heavy targets and
larger angles added in 7.1 ● A better alternative to the LEP elastic model, but:
– effective lower energy limit = 1 GeV
– not valid for A < 4, A > 208
– slower
– requires cross section table to be downloaded
Elastic proton scattering from 28Si (1 GeV)
Elastic proton scattering from 4He (301 GeV)
Highlights: Extension of Bertini cascade model to strange particles
● requires pre-compiler flag G4BERTINI_KAON to be set when building Geant4 libraries
● now valid for:
– p, n, +,L0
S+,-, 0,-,-
– GeV
● A better alternative to the LEP elastic model for low and intermediate energies
705 MeV/c K+ quasi-elastic scattering from C
705 MeV/c K+ quasi-elastic scattering from Pb
Highlights: Fixes and Tuning
● Memory leaks fixed in:– RadioactiveDecay
– De-excitation handler
– Abrasion/Ablation model
● Physics tuning of CHIPS model for anti-proton annihilation at rest
● Isotope production code now supplies name of hadronic model that produced it
● Corrected momentum balance for elastic scattering final states
Summary
● Development plans– extending ion interaction codes to higher mass nuclei
– add decay information and new decay modes to radioactive decay table
– continued improvement of LEP, Bertini and Binary cascade models
– expanded use of CHIPS model for mu-nuclear, neutrino and high energy modeling
● Release 7.1 highlights– new, improved elastic scattering model (coherent elastic)
– kaon extension of Bertini cascade model